erlang(3)

MODULE
erlang - The Erlang BIFs

DESCRIPTION

By convention, Built In Functions (BIFs) are seen as being in the module erlang. Thus, both the calls atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical.

BIFs may fail for a variety of reasons. All BIFs fail if they are called with arguments of an incorrect type. For example, atom_to_list/1 will fail if it is called with an argument which is not an atom. If this type of failure is not within the scope of a catch (and the BIF is not called within a guard; see below), the process making the call will exit, and an EXIT signal with the associated reason badarg will be sent to all linked processes. The other reasons that may make BIFs fail are described in connection with the description of each individual BIF.

A few BIFs may be used in guard tests, for example:
tuple_5(Something) when size(Something) == 5 ->
    is_tuple_size_5;
tuple_5(_) ->
    is_something_else.

Here the BIF size/1 is used in a guard. If size/1 is called with a tuple, it will return the size of the tuple (i.e., how many elements there are in the tuple). In the above example, size/1 is used in a guard which tests if its argument Something is a tuple and, if it is, whether it is of size 5. In this case, calling size with an argument other than a tuple will cause the guard to fail and execution will continue with the next clause. Suppose tuple_5/1 is written as follows:
tuple_5(Something) ->
    case size(Something) of
         5 -> is_tuple_size_5;
                 _ -> is_something_else
            end.

In this case, size/1 is not in a guard. If Something is not a tuple, size/1 will fail and cause the process to exit with the associated reason badarg (see above).

Some of the BIFs in this chapter are optional in Erlang implementations, and not all implementations will include them.

The following descriptions indicate which BIFs can be used in guards and which BIFs are optional.

EXPORTS

abs(Number)

    Returns an integer or float which is the arithmetical absolute value of the argument Number (integer or float).
    > abs(-3.33).
    3.33000
    > abs(-3).
    3

    This BIF is allowed in guard tests.

    Failure: badarg if the argument is not an integer or a float.

erlang:append_element(Tuple, Term)

    Returns a new tuple which has one element more than Tuple, and contains the elements in Tuple followed by Term as the last element. Semantically equivalent to list_to_tuple(tuple_to_list(Tuple ++ [Term]), but much faster.

    Failure: badarg if Tuple is not a tuple.

apply({Module, Function}, ArgumentList)

    This is equivalent to apply(Module, Function, ArgumentList).

apply(Module, Function, ArgumentList)

    Returns the result of applying Function in Module on ArgumentList. The applied function must have been exported from Module. The arity of the function is the length of ArgumentList.
    > apply(lists, reverse, [[a, b, c]]).
    [c,b,a]

    apply can be used to evaluate BIFs by using the module name erlang.
    > apply(erlang, atom_to_list, ['Erlang']).
    "Erlang"

    Failure: error_handler:undefined_function/3 is called if Module has not exported Function/Arity. The error handler can be redefined (see the BIF process_flag/2). If the error_handler is undefined, or if the user has redefined the default error_handler so the replacement module is undefined, an error with the reason undef will be generated.

atom_to_list(Atom)

    Returns a list of integers (Latin-1 codes), which corresponds to the text representation of the argument Atom.
    >atom_to_list('Erlang').
    "Erlang"

    Failure: badarg if the argument is not an atom.

erlang:binary_to_float(Binary)

    Returns a float corresponding to the big-endian IEEE representation in Binary. The size of Binary must be 4 or 8 bytes.

  Warning:

This is an internal BIF, only to be used by OTP code.

Failure: badarg if the argument is not a binary or not the representation of a number.

binary_to_list(Binary)

    Returns a list of integers which correspond to the bytes of Binary.

binary_to_list(Binary, Start, Stop)

    As binary_to_list/1, but it only returns the list from position Start to position Stop. Start and Stop are integers. Positions in the binary are numbered starting from 1.

binary_to_term(Binary)

    Returns an Erlang term which is the result of decoding the binary Binary. Binary is encoded in the Erlang external binary representation. See term_to_binary/1.

erlang:bump_reductions(Reductions)

    This implementation-dependent function increments the reduction counter for the current process. In the Beam emulator, the reduction counter is normally incremented by one for each function and BIF call, and a context switch is forced when the counter reaches 1000.

  Warning:

This BIF might be removed in a future version of the Beam machine without prior warning. It is unlikely to be implemented in other Erlang implementations. If you think that you must use it, encapsulate it your own wrapper module, and/or wrap it in a catch.

erlang:cancel_timer(Ref)

    cancel_timer(Ref) cancels a timer, where Ref was returned by either send_after/3 or start_timer/3. If the timer was there to be removed, cancel_timer/1 returns the time in ms left until the timer would have expired, otherwise false (which may mean that Ref was never a timer, or that it had already been cancelled, or that it had already delivered its message).

    Note: usually, cancelling a timer does not guarantee that the message has not already been delivered to the message queue. However, in the special case of a process P cancelling a timer which would have sent a message to P itself, attempting to read the timeout message from the queue is guaranteed to remove the timeout in that situation:
            cancel_timer(Ref),
            receive
                {timeout, Ref, _} ->
                    ok
            after 0 ->
                    ok
            end

    Failure: badarg if Ref is not a reference.

erlang:check_process_code(Pid, Module)

    Returns true if the process Pid is executing an old version of Module, if the current call of the process executes code for an old version of the module, if the process has references to an old version of the module, or if the process contains funs that references the old version of the module. Otherwise, it returns false.
    > erlang:check_process_code(Pid, lists).
    false

    This is an optional BIF.

    Failure: badarg, if the process argument is not a Pid, or the module argument is not an atom.

concat_binary(ListOfBinaries)

    Concatenates a list of binaries ListOfBinaries into one binary.

date()

    Returns the current date as {Year, Month, Day}
    > date().
    {1995, 2, 19}

erlang:delete_module(Module)

    Moves the current version of the code of Module to the old version and deletes all export references of Module. Returns undefined if the module does not exist, otherwise true.
    > delete_module(test).
    true

    This is an optional BIF.

    Failure: badarg if there is already an old version of the module (see BIF purge_module/1).

  Warning:

In normal Erlang implementations code handling - which includes loading, deleting, and replacing modules - is performed in the module code. This BIF is intended for use with the implementation of the module code and should not be used elsewhere.

erlang:demonitor(Ref)

    If Ref is a reference which the current process obtained by calling erlang:monitor/2, the monitoring is turned off. No action is performed if the monitoring already is turned of before the call. Returns true.

    After the call to erlang:monitor/2 the monitoring process will not get any new 'DOWN' message from this monitor into the receive queue.

    It is an error if Ref refers to a monitoring started by another process. Not all such cases are cheap to check; if checking is cheap, the call fails with badarg (for example if Ref is a remote reference).

erlang:disconnect_node(Node)

    Forces the disconnection of a node. This will appear to the node Node as if the current node has crashed. This BIF is mainly used in the Erlang network authentication protocols. Returns true if disconnection succeeds, otherwise false.

    Failure: badarg if Node is not an atom.

erlang:display(Term)

    Prints a text representation Term on the standard output. Useful for debugging (especially startup problems) and strongly discouraged for other purposes.

element(N, Tuple)

    Returns the Nth element (numbering from 1) of Tuple.
    > element(2, {a, b, c}).
    b

    Failure: badarg if N < 1, or N > size(Tuple), or if the argument Tuple is not a tuple. Allowed in guard tests.

erase()

    Returns the process dictionary and deletes it.
    > put(key1, {1, 2, 3}), put(key2, [a, b, c]), erase().
    [{key1,{1, 2, 3}},{key2,[a, b, c]}]

erase(Key)

    Returns the value associated with Key and deletes it from the process dictionary. Returns undefined if no value is associated with Key. Key can be any Erlang term.
    > put(key1, {merry, lambs, are, playing}),
      X = erase(key1), {X, erase(key1)}.
    {{merry, lambs, are, playing}, undefined}

exit(Reason)

    Stops the execution of the current process with the reason Reason. Can be caught. Reason is any Erlang term. Since evaluating this function causes the process to terminate, it has no return value.
    > exit(foobar).
    ** exited: foobar **
    > catch exit(foobar).
    {'EXIT', foobar}

exit(Pid, Reason)

    Sends an EXIT message to the process Pid. Returns true.
    > exit(Pid, goodbye).
    true

  Note:

The above is not necessarily the same as:
Pid ! {'EXIT', self(), goodbye}

The above two alternatives are the same if the process with the process identity Pid is trapping exits. However, if Pid is not trapping exits, the Pid itself will exit and propagate EXIT signals in turn to its linked processes.

If the reason is the atom kill, for example exit(Pid, kill), an untrappable EXIT signal will be sent to the process Pid. In other words, the process Pid will be unconditionally killed.

Returns true.

Failure: badarg if Pid is not a Pid.

erlang:fault(Reason)

    Stops the execution of the current process with the reason Reason, where Reason is any Erlang term. The actual EXIT term will be {Reason, Where}, where Where is a list of the functions most recently called (the current function first). Since evaluating this function causes the process to terminate, it has no return value.

erlang:fault(Reason, Args)

    Stops the execution of the current process with the reason Reason, where Reason is any Erlang term. The actual EXIT term will be {Reason, Where}, where Where is a list of the functions most recently called (the current function first). The Args is expected to be the arguments for the current function; in Beam it will be used to provide the actual arguments for the current function in the Where term. Since evaluating this function causes the process to terminate, it has no return value.

float(Number)

    Returns a float by converting Number to a float.
    > float(55).
    55.0000

  Note:

float/1 is allowed in guard tests, but it tests whether the argument is a float or not.
-module(t).
f(F) when float(F) -> float;
f(F) -> not_a_float.
1> t:f(1).
not_a_float
2> t:f(1.0).
float
3>

Failure: badarg if the argument is not a float or an integer.

erlang:float_to_binary(Float, Size)

    Returns a binary containing the big-endian IEEE representation of Float. Size is the size in bits, and must be either 32 or 64.

  Warning:

This is an internal BIF, only to be used by OTP code.

Failure: badarg if the argument is not a float.

float_to_list(Float)

    Returns a list of integers (ASCII codes) which corresponds to Float.
    > float_to_list(7.0).
    "7.00000000000000000000e+00"

    Failure: badarg if the argument is not a float.

erlang:fun_info(Fun)

    Returns a list containing information about the fun Fun. This BIF is only intended for debugging. The list returned contains the following tuples, not necessarily in the order listed here (i.e., you should not depend on the order).

        {pid, Pid}:
            Pid is the pid of the process that originally created the fun. It will be the atom undefined if the fun is given in the tuple representation.

        {module, Module}:
            Module (an atom) is the module in which the fun is defined.

        {name, Name}:
            Name is the name of the (non-exported) function that implements the fun.

        {name, Name}:
            Name is the name of the local function that implements the fun. If no code is currently loaded for the fun, [] will be returned instead of an atom.

        {arity, Arity}:
            Arity is the number of arguments that the fun should be called with.

        {index, Index}:
            Index (an integer) is an index into the module's fun table.

        {uniq, Uniq}:
            Uniq (an integer) is a unique value for this fun.

        {env, Env}:
            Env (a list) is the environment or free variables for the fun.

erlang:fun_info(Fun, Item)

    Returns information about the Fun as specified by Item, in the form {Item, Info}. Item can be any of the atoms id, module, index, uniq, name, arity, or env. See the erlang:fun_info/1 BIF.

erlang:fun_to_list(Fun)

    Returns a textual representation of the fun Fun.

erlang:function_exported(Module, Function, Arity)

    Returns true if the module Module is loaded and it contains an exported function Function/Arity; otherwise returns false. Returns false for any BIF (functions implemented in C rather than in Erlang).

    This function is retained mainly for backwards compatibility. It is not clear why you really would want to use it.

erlang:garbage_collect()

    Forces an immediate garbage collection of the currently executing process. You should not use erlang:garbage_collect() unless you have noticed or have good reasons to suspect that the spontaneous garbage collection will occur too late or not at all. Improper use may seriously degrade system performance.

    Compatibility note: In versions of OTP prior to R7, the garbage collection took place at the next context switch, not immediately. To force a context switch after a call to erlang:garbage_collect(), it was sufficient to make any function call.

erlang:garbage_collect(Pid)

    Works like erlang:garbage_collect() but on any process. The same caveats apply. Returns false if Pid refers to a dead process; true otherwise.

get()

    Returns the process dictionary as a list of {Key, Value} tuples.
    > put(key1, merry), put(key2, lambs),
      put(key3, {are, playing}), get().
    [{key1, merry}, {key2, lambs}, {key3, {are, playing}}]

get(Key)

    Returns the value associated with Key in the process dictionary, and undefined if no value is associated with Key. Key can be any Erlang term.
    > put(key1, merry), put(key2, lambs),
      put({any, [valid, term]}, {are, playing}),
      get({any, [valid, term]}).
    {are, playing}

erlang:get_cookie()

    Returns the "magic cookie" of the current node, if the node is alive; otherwise the atom nocookie.

get_keys(Value)

    Returns a list of keys which corresponds to Value in the process dictionary.
    > put(mary, {1, 2}), put(had, {1, 2}), put(a, {1, 2}),
      put(little, {1, 2}), put(dog, {1, 3}), put(lamb, {1, 2}),
      get_keys({1, 2}).
    [mary, had, a, little, lamb]

group_leader()

    Every process is a member of some process group and all groups have a leader.

    This BIF returns the process identifier Pid of the group leader for the process which evaluates the BIF. When a process is spawned, the group leader of the spawned process is the same as that of the process which spawned it. Initially, at system start-up, init is both its own group leader and the group leader of all processes.

group_leader(Leader, Pid)

    Sets the group leader of Pid to Leader. Typically, this is used when a processes started from a certain shell should have another group leader than init. The process Leader is normally a process with an I/O protocol. All I/O from this group of processes are thus channeled to the same place.

halt()

    Halts the Erlang runtime system and indicates normal exit to the calling environment. Has no return value.
    > halt().
    unix_prompt%

halt(Status)

    Status must be a non-negative integer, or a string. Halts the Erlang runtime system. Has no return value. If Status is an integer, it is returned as an exit status of Erlang to the calling environment. If Status is a string, produces an Erlang crash dump with String as slogan, and then exits with a non-zero status code.

    Note that on many platforms, only the status codes 0-255 are supported by the operating system.

erlang:hash(Term, Range)

    Returns a hash value for Term within the range 1..Range. The allowed range is 1..2^27-1.

  Warning:

This BIF is deprecated as the hash value may differ on different architectures. Also the hash values for integer terms larger than 2^27 as well as large binaries are very poor. The BIF is retained for backward compatibility reasons (it may have been used to hash records into a file), but all new code should use one of the BIFs erlang:phash/2 or erlang:phash2/1, 2 instead.

hd(List)

    Returns the first item of List.
    > hd([1,2,3,4,5]).
    1

    Allowed in guard tests.

    Failure: badarg if List is the empty list [], or is not a list.

erlang:hibernate(Module, Function, ArgumentList)

    erlang:hibernate/3 gives a way to put a process into a wait state where its memory allocation has been reduced as much as possible, which is useful if the process does not expect to receive any messages in the near future.

    The process will be awaken when a message is sent to it, and control will resume in Module:Function with the arguments given by ArgumentList with the call stack emptied, meaning that the process will terminate when that function returns. Thus erlang:hibernate/3 will never return to its caller.

    If the process has any message in its message queue, the process will be awaken immediately in the same way as described above.

    In more technical terms, what erlang:hibernate/3 will do is the following. It will discard the call stack for the process. Then it will garbage collect the process. After the garbage collection, all live data will be in one contionous heap. The heap will then be shrunk to the exact same size as the live data which it holds (even if that size should be less than the minimum heap size for the process).

    If the size of the live data in the process is less than the minimum heap size, the first garbage collection occurring after the process has been awaken will ensure that the heap size is changed to a size not smaller than the minimum heap size.

    Failure: badarg if Module and/or Function is not an atom, or if ArgumentList is not a list.

erlang:info(What)

    This BIF is now equivalent to erlang:system_info/1.

integer_to_list(Integer)

    Returns a list of integers (ASCII codes) which correspond to Integer.
    > integer_to_list(77).
    "77"

    Failure: badarg if the argument is not an integer.

integer_to_list(Integer, Base)

    Returns a list of integers (ASCII codes) in base Base which correspond to Integer.
    > integer_to_list(1023, 16).
    "3FF"

    Failure: badarg if Integer or Base is not integers, or if Base is not in the range 2 through 36.

is_alive()

    Returns the atom true if the current node is alive; i.e., if the node can be part of a distributed system. Otherwise, it returns the atom false.

erlang:is_builtin(Module, Function, Arity)

    Returns true if Module:Function/Arity is a BIF implemented in C; otherwise returns false. This BIF is useful for builders of cross reference tools.

is_process_alive(Pid)

    Pid must refer to a process on the current node. Returns the atom true if the process is alive, i.e., has not exited. Otherwise, it returns the atom false.

length(List)

    Returns the length of List.
    > length([1,2,3,4,5,6,7,8,9]).
    9

    Allowed in guard tests.

    Failure: badarg if the argument is not a proper list.

link(Pid)

    Creates a link to the process (or port) Pid, if there is not such a link already. If a process attempts to create a link to itself, nothing is done. Returns true.

    Failure: badarg if the argument is not a Pid or port. Sends the EXIT signal noproc to the process which evaluates link if the argument is the Pid of a process which does not exist.

list_to_atom(CharIntegerList)

    Returns an atom whose text representation is the integers (Latin-1 codes) in CharIntegerList.
    > list_to_atom([69, 114, 108, 97, 110, 103]).
    'Erlang'

    Failure: badarg if the argument is not a list of integers, or if any integer in the list is not an integer in the range [0, 255].

list_to_binary(List)

    Returns a binary which is made from the integers and binaries in List. List may be deep and may contain any combination of integers and binaries.

    Example: list_to_binary([Bin1, 1, [2, 3, Bin2], 4|Bin3])

    Failure: badarg if the argument is not a list, or if the list or any sublist contains anything else than binaries or integers in the range [0, 255].

list_to_float(AsciiIntegerList)

    Returns a float whose text representation is the integers (ASCII-values) in AsciiIntegerList.
    > list_to_float([50,46,50,48,49,55,55,54,52,101,43,48]).
    2.20178

    Failure: badarg if the argument is not a list of integers, or if AsciiIntegerList contains a bad representation of a float.

list_to_integer(AsciiIntegerList)

    Returns an integer whose text representation is the integers (ASCII-values) in AsciiIntegerList.
    > list_to_integer([49, 50, 51]).
    123

    Failure: badarg if the argument is not a list of integers, or if AsciiIntegerList contains a bad representation of an integer.

list_to_integer(AsciiIntegerList, Base)

    Returns an integer whose text representation in base Base is the integers (ASCII-values) in AsciiIntegerList.
    > list_to_integer("3FF", 16).
    1023

    Failure: badarg if the AsciiIntegerList is not a list of integers, contains a bad representation of an integer, or if Base is not in the range 2 through 36.

list_to_pid(AsciiIntegerList)

    Returns a Pid whose text representation is the integers (ASCII-values) in AsciiIntegerList. This BIF is intended for debugging, and in the Erlang operating system. It should not be used in application programs.
    > list_to_pid("<0.4.1>").
    <0.4.1>

    Failure: badarg if the argument is not a list of integers, or AsciiIntegerList contains a bad representation of a Pid.

list_to_tuple(List)

    Returns a tuple which corresponds to List. List can contain any Erlang terms.
    > list_to_tuple([mary, had, a, little, {dog, cat, lamb}]).
    {mary, had, a, little, {dog, cat, lamb}}

    Failure: badarg if List is not a proper list.

erlang:load_module(Module, Binary)

    If Binary contains the object code for the module Module, this BIF loads that object code. Also, if the code for the module Module already exists, all export references are replaced so they point to the newly loaded code. The previously loaded code is kept in the system as `old code', as there may still be processes which are executing that code. It returns either {module, Module}, where Module is the name of the module which has been loaded, or {error, Reason} if load fails. Reason is one of the following:

        badfile:
            If the object code in Binary has an incorrect format.

        not_purged:
            If Binary contains a module which cannot be loaded because old code for this module already exists (see the BIFs purge_module and delete_module).

        badfile:
            If the object code contains code for another module than Module

  Warning:

Code handling - which includes loading, deleting, and replacing of modules - is done by the module code in normal Erlang implementations. This BIF is intended for the implementation of the module named code and should not be used elsewhere.

This is an optional BIF.

Failure: badarg if the first argument is not an atom, or the second argument is not a binary.

erlang:loaded()

    Returns a list of all loaded Erlang modules, including preloaded modules. A module will be included in the list if it has either current code or old code or both loaded.

erlang:localtime()

    Returns the current local date and time {{Year, Month, Day}, {Hour, Minute, Second}}.

    The time zone and daylight saving time correction depend on the underlying OS.
    > erlang:localtime().
    {{1996,11,6},{14,45,17}}

erlang:localtime_to_universaltime(DateTime)

    Converts local date and time in DateTime to Universal Time Coordinated (UTC), if this is supported by the underlying OS. Otherwise, no conversion is done and DateTime is returned. The return value is of the form {{Year, Month, Day}, {Hour, Minute, Second}}.

    Failure: badarg if the argument is not a valid date and time tuple {{Year, Month, Day}, {Hour, Minute, Second}}.
    > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
    {{1996,11,6},{13,45,17}}

erlang:localtime_to_universaltime(DateTime, IsDst)

    Converts local date and time in DateTime to Universal Time Coordinated (UTC) just like erlang:localtime_to_universaltime/1, but the caller decides if daylight saving time is active or not.

    If IsDst == true the DateTime is during daylight saving time, if IsDst == false it is not, and if IsDst == undefined the underlying OS may guess, which is the same as calling erlang:localtime_to_universaltime(DateTime).

    Failure: badarg if DateTime is not a valid date and time tuple {{Year, Month, Day}, {Hour, Minute, Second}} or if IsDst is not one of the atoms true, false or undefined.
    > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
    {{1996,11,6},{12,45,17}}
    > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
    {{1996,11,6},{13,45,17}}
    > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
    {{1996,11,6},{13,45,17}}

make_ref()

    Returns an almost unique reference.

    The returned reference will reoccur after approximately 2^82 calls; therefore it is unique enough for most practical purposes.
    > make_ref().
    #Ref<0.0.0.135>

erlang:make_tuple(Arity, InitialValue)

    Returns a new tuple of the given Arity, where all elements are InitialValue.
    > erlang:make_tuple(4, []).
    {[],[],[],[]}

erlang:md5(Data) -> Digest

    Types
        Data = iolist() | binary()
        Digest = binary()

    Computes an MD5 message digest from Data, where the length of the digest is 128 bits (16 bytes). Data is a binary or a list of small integers and binaries.

    See The MD5 Message Digest Algorithm (RFC 1321) for more information about MD5.

    Failure: badarg if the Data argument is not a list, or if the list or any sublist contains anything else than binaries or integers in the range [0, 255].

erlang:md5_final(Context) -> Digest

    Types
        Context = Digest = binary()

    Finishes the update of an MD5 Context and returns the computed MD5 message digest.

erlang:md5_init() -> Context

    Types
        Context = binary()

    Creates an MD5 context, to be used in subsequent calls to md5_update/2.

erlang:md5_update(Context, Data) -> NewContext

    Types
        Data = iolist() | binary()
        Context = NewContext = binary()

    Updates an MD5 Context with Data, and returns a NewContext.

erlang:memory() -> MemList

    Types
        MemList = [MemInfo]
        MemInfo = {atom(), int()}

    erlang:memory/0 returns information about memory dynamically allocated by the Erlang emulator.

    A list of tuples is returned. Each tuple has two elements. The first element is an atom describing memory type. The second element is memory size in bytes. A description of each tuple follows:

        total:
            The total amount of memory currently allocated. total is the sum of processes and system.

        processes:
            The total amount of memory currently allocated by the Erlang processes.

        processes_used:
            The total amount of memory currently used by the Erlang processes.

            This memory is part of the memory presented as processes memory.

        system:
            The total amount of memory currently allocated by the emulator that isn't directly related to an Erlang process.

            Memory presented as processes is not included in this memory.

        atom:
            The total amount of memory currently allocated for atoms.

            This memory is part of the memory presented as system memory.

        atom_used:
            The total amount of memory currently used for atoms.

            This memory is part of the memory presented as atom memory.

        binary:
            The total amount of memory currently allocated for binaries.

            This memory is part of the memory presented as system memory.

        code:
            The total amount of memory currently allocated for Erlang code.

            This memory is part of the memory presented as system memory.

        ets:
            The total amount of memory currently allocated for ets tables.

            This memory is part of the memory presented as system memory.

        maximum:
            The maximum total amount of memory allocated since the emulator was started.

            This tuple is only present when the emulator is run with instrumentation.

            For information on how to run the emulator with instrumentation see the instrument(3) and/or erl(1) man pages.

  Note:

The system value is not complete. Some allocated memory that should be part of the system value are not. For example, memory allocated by drivers are missing.

When the emulator is run with instrumentation, the system value is more accurate, but memory directly allocated by malloc (and friends) are still not part of the system value. Direct calls to malloc are only done from OS specific runtime libraries and perhaps from user implemented Erlang drivers that do not use the memory allocation functions in the driver interface.

Since the total value is the sum of processes and system the error in system will propagate to the total value.

The different values has the following relation to each other. Values beginning with an uppercase letter is not part of the result.
        total = processes + system
        processes = processes_used + ProcessesNotUsed
        system = atom + binary + code + ets + OtherSystem
        atom = atom_used + AtomNotUsed
        RealTotal = processes + RealSystem
        RealSystem = system + MissedSystem

  Note:

The total value is supposed to be the total amount of memory dynamically allocated by the emulator. Shared libraries, the code of the emulator itself, and the emulator stack(s) are not supposed to be included. That is, the total value is not supposed to be equal to the total size of all pages mapped to the emulator. Furthermore, due to fragmentation and pre-reservation of memory areas, the size of the memory segments which contain the dynamically allocated memory blocks can be substantially larger than the total size of the dynamically allocated memory blocks.

More tuples in the returned list may be added in the future.

erlang:memory(MemoryTypeSpec) -> MemList | int()

    Types
        MemoryTypeSpec = MemoryType | [MemoryType]
        MemoryType = atom()
        MemList = [MemInfo]
        MemInfo = {atom(), int()}

    erlang:memory/1 returns the same type of information as erlang:memory/0, but allows the caller to select specific information.

    MemoryType is an atom equal to any atom that is used by erlang:memory/0 to describe a memory type.

    When MemoryTypeSpec is an atom the corresponding memory size is returned as an integer.

    When MemoryTypeSpec is a list of atoms the corresponding values are returned as a MemList. The elements of the list returned are sorted, with regard to the atoms, in the same order as the MemoryTypeSpec list is sorted with the exception that duplicate atoms are ignored.

    Failure: badarg if MemoryType isn't an atom that is used by erlang:memory/0 to describe a memory type, or if the emulator isn't run with instrumentation and maximum is used as a MemoryType.

erlang:module_loaded(Module)

    Returns the atom true if the module contained in atom Module is loaded, otherwise it returns the atom false. It does not attempt to load the module.

  Warning:

This BIF is intended for the implementation of the module named code and should not be used anywhere else. Use code:is_loaded/1 instead.
> erlang:module_loaded(lists).
true

This is an optional BIF.

Failure: badarg if the argument is not an atom.

erlang:monitor(Type, Item) -> MonitorReference

    Types
        MonitorReference = reference()
        Type = atom()
        Item = pid() | {RegisteredName, NodeName} | RegisteredName
        RegisteredName = atom()
        NodeName = atom()

    The current process starts monitoring Item which is an object of type Type.

    Currently only processes can be monitored, i.e. the only allowed Type is process, but other types may be allowed in the future.

    Valid Items when Type is process are:

        pid():
            The pid of the process to monitor.

        {RegisteredName, NodeName}:
            A tuple consisting of a registered name of a process and a node name. The process residing on the node NodeName with the registered name RegisteredName will be monitored.

        RegisteredName:
            The same as {RegisteredName, node()}.

  Note:

When a process is monitored by registered name, the process that has the registered name at the time when erlang:monitor/2 is called will be monitored. The monitor will not be effected, if the registered name is unregistered.

A 'DOWN' message will be sent to the monitoring process if Item dies, if Item doesn't exist, or if the connection is lost to the node which Item resides on. A 'DOWN' message has the following pattern:

{'DOWN', MonitorReference, Type, Object, Info} where:

    MonitorReference:
        The reference returned by erlang:monitor/2.

    Type:
        The type of the monitored object.

    Object:
        A reference to the monitored object.

        When Type is process, Object will be:

            *   the pid of the monitored process, if Item was the pid in the call to erlang:monitor/2.

            *   {RegisteredName, NodeName}, if Item was {RegisteredName, NodeName} in the call to erlang:monitor/2.

            *   {RegisteredName, NodeName}, if Item was RegisteredName in the call to erlang:monitor/2. NodeName will in this case be the name of the local node.

    Info:
        When Type is process, Info is either the exit reason of the process, noproc (non-existing process), or noconnection (no connection to Items node).

  Note:

If/when erlang:monitor/2 is extended (e.g. to handle other item types than process), other possible values for Type, Object, and Info in the 'DOWN' message will be introduced.

The monitoring is turned off either when the 'DOWN' message is sent, or when erlang:demonitor(MontiorReference) is called (MontiorReference is the value returned by erlang:monitor/2).

If an attempt is made to monitor a process on an older node (where remote process monitoring is not implemented or one where remote process monitoring by registered name is not implemented), the call fails with badarg.

Making several calls to erlang:monitor/2 for the same Item is not an error; it results in several completely independent monitorings.

  Note:

The format of the 'DOWN' message changed in the 5.2 version of the emulator (OTP release R9B) for monitor by registered name. The Object element of the 'DOWN' message could in earlier versions sometimes be the pid of the monitored process and sometimes be the registered name. Now the Object element is always a tuple consisting of the registered name and the node name. Processes on new nodes (emulator version 5.2 or greater) will always get 'DOWN' messages on the new format even if they are monitoring processes on old nodes. Processes on old nodes will always get 'DOWN' messages on the old format.

monitor_node(Node, Flag)

    Monitors the status of the node Node. If Flag is true, monitoring is turned on; if Flag is false, monitoring is turned off. Calls to the BIF are accumulated. This is shown in the following example, where a process is already monitoring the node Node and a library function is called:
    monitor_node(Node, true),
        ...  some operations
    monitor_node(Node, false),

    After the call, the process is still monitoring the node.

    If Node fails or does not exist, the message {nodedown, Node} is delivered to the process. If a process has made two calls to monitor_node(Node, true) and Node terminates, two nodedown messages are delivered to the process. If there is no connection to Node, there will be an attempt to create one. If this fails, a nodedown message is delivered.

    Nodes connected through hidden connections can be monitored as any other node with erlang:monitor_node/2.

    Returns true.

    Failure: badarg if Flag is not true or false, and badarg if Node is not an atom indicating a remote node, or if the local node is not alive.

node()

    Returns the name of the current node. If it is not a networked node but a local Erlang runtime system, the atom nonode@nohost is returned.

    Allowed in guard tests.

node(Arg)

    Returns the node where Arg is located. Arg can be a Pid, a reference, or a port.

    Allowed in guard tests.

    Failure: badarg if Arg is not a Pid, reference, or port.

nodes()

    Returns a list of all visible nodes in the system, excluding the current node. Same as nodes(visible).

nodes(Arg)

    Types
        Arg = ArgList | ArgAtom
        ArgList = [ArgAtom]
        ArgAtom = visible | hidden | connected | this | known

    Returns a list of nodes according to argument given. The result returned when Arg is an ArgList is the list of nodes satisfying the disjunction(s) of ArgAtoms in the ArgList.

    ArgAtom description:

        visible:
            Nodes connected to this node through normal connections.

        hidden:
            Nodes connected to this node through hidden connections.

        connected:
            Nodes connected to this node.

        this:
            This node.

        known:
            Nodes which are known to this node, i.e., connected, previously connected, etc.

    More ArgAtoms may be added in the future.

    Some equalities: [node()] = nodes(this), nodes(connected) = nodes([visible, hidden]), and nodes() = nodes(visible).

    Failure: badarg if argument isn't an ArgAtom or a list of ArgAtoms.

now()

    Returns the tuple {MegaSecs, Secs, Microsecs}

    which is the elapsed time since 00:00 GMT, January 1, 1970 (zero hour) on the assumption that the underlying OS supports this. Otherwise, some other point in time is chosen. It is also guaranteed that subsequent calls to this BIF returns continuously increasing values. Hence, the return value from now() can be used to generate unique time-stamps. It can only be used to check the local time of day if the time-zone info of the underlying operating system is properly configured.

open_port(PortName, PortSettings)

    Returns a port identifier as the result of opening a new Erlang port. A port can be seen as an external Erlang process. PortName is one of the following:

        {spawn, Command}:
            Starts an external program. Command is the name of the external program which will be run. Command runs outside the Erlang work space unless an Erlang driver with the name Command is found. If found, that driver will be started. A driver runs in the Erlang workspace, which means that it is linked with the Erlang runtime system.

            When starting external programs on Solaris, the system call vfork is used in preference to fork for performance reasons, although it has a history of being less robust. If there are problems with using vfork, setting the environment variable ERL_NO_VFORK to any value will cause fork to be used instead.

        Atom:
            This use of open_port() is obsolete and will be removed in a future version of Erlang. Use the file module instead. The atom is assumed to be the name of an external resource. A transparent connection is established between Erlang and the resource named by the atom Atom. The characteristics of the port depend on the type of resource. If Atom represents a normal file, the entire contents of the file is sent to the Erlang process as one or more messages. When messages are sent to the port, it causes data to be written to the file.

        {fd, In, Out}:
            Allows an Erlang process to access any currently opened file descriptors used by Erlang. The file descriptor In can be used for standard input, and the file descriptor Out for standard output. It is only used for various servers in the Erlang operating system (shell and user). Hence, its use is very limited.

    PortSettings is a list of settings for the port. Valid values are:

        {packet, N}:
            Messages are preceded by their length, sent in N bytes, with the most significant byte first. Valid values for N are 1, 2, or 4.

        stream:
            Output messages are sent without packet lengths. A user-defined protocol must be used between the Erlang process and the external object.

        {line, N}:
            Messages are delivered on a per line basis. Each line (delimited by the OS-dependent newline sequence) is delivered in one single message. The message data format is {Flag, Line}, where Flag is either eol or noeol and Line is the actual data delivered (without the newline sequence).

            N specifies the maximum line length in bytes. Lines longer than this will be delivered in more than one message, with the Flag set to noeol for all but the last message. If end of file is encountered anywhere else than immediately following a newline sequence, the last line will also be delivered with the Flag set to noeol. In all other cases, lines are delivered with Flag set to eol.

            The {packet, N} and {line, N} settings are mutually exclusive.

        {cd, Dir}:
            This is only valid for {spawn, Command}. The external program starts using Dir as its working directory. Dir must be a string. Not available on VxWorks.

        {env, Environment}:
            This is only valid for {spawn, Command}. The environment of the started process is extended using the environment specifications in Environment. Environment should be a list of tuples {Name, Value}, where Name is the name of an environment variable, and Value is the value it is to have in the spawned port process. Both Name and Value must be strings. The one exception is Value being the atom false (in analogy with os:getenv/1), which removes the environment variable. Not available on VxWorks.

        exit_status:
            This is only valid for {spawn, Command} where Command refers to an external program. When the external process connected to the port exits, a message of the form {Port, {exit_status, Status}} is sent to the connected process, where Status is the exit status of the external process. If the program aborts, on Unix the same convention is used as the shells do (i.e., 128+signal). If the eof option has been given as well, the eof message and the exit_status message appear in an unspecified order. If the port program closes its stdout without exiting, the exit_status option will not work.

        use_stdio:
            This is only valid for {spawn, Command}. It allows the standard input and output (file descriptors 0 and 1) of the spawned (UNIX) process for communication with Erlang.

        nouse_stdio:
            The opposite of the above. Uses file descriptors 3 and 4 for communication with Erlang.

        stderr_to_stdout:
            Affects ports to external programs. The executed program gets its standard error file redirected to its standard output file. stderr_to_stdout and nouse_stdio are mutually exclusive.

        in: The port can only be used for input.

        out:
            The port can only be used for output.

        binary:
            All I/O from the port are binary data objects as opposed to lists of bytes.

        eof:
            The port will not be closed at the end of the file and produce an EXIT signal. Instead, it will remain open and a {Port, eof} message will be sent to the process holding the port.

    The default is stream for all types of port and use_stdio for spawned ports.

    Failure: badarg if the format of PortName or PortSettings is incorrect. If the port cannot be opened, the exit reason is the Posix error code which most closely describes the error, or einval if no Posix code is appropriate. The following Posix error codes may appear:

        enomem:
            There was not enough memory to create the port.

        eagain:
            There are no more available operating system processes.

        enametoolong:
            The external command given was too long.

        emfile:
            There are no more available file descriptors.

        enfile:
            A file or port table is full.

    During use of a port opened using {spawn, Name}, errors arising when sending messages to it are reported to the owning process using exit signals of the form {'EXIT', Port, PosixCode}. Posix codes are listed in the documentation for the file module.

    The maximum number of ports that can be open at the same time is 1024 by default, but can be configured by the environment variable ERL_MAX_PORTS.

erlang:phash(Term, Range)

    Portable hash function that will give the same hash for the same erlang term regardless of machine architecture and ERTS version (The BIF was introduced in ERTS 4.9.1.1). Range can be between 1 and 2^32, the function returns a hash value for Term within the range 1..Range.

    This BIF could be used instead of the old deprecated erlang:hash/2 BIF, as it calculates better hashes for all datatypes, but consider using phash2/1, 2 instead.

erlang:phash2(Term [, Range])

    Portable hash function that will give the same hash for the same erlang term regardless of machine architecture and ERTS version (The BIF was introduced in ERTS 5.2). Range can be between 1 and 2^32, the function returns a hash value for Term within the range 0..Range-1. When called without the Range argument, a value in the range 0..2^27-1 is returned.

    This BIF should always be used for hashing terms. It distributes small integers better than phash/2, and it is faster for bignums and binaries.

    Note that the range 0..Range-1 is different from the range of phash/2 (1..Range).

pid_to_list(Pid)

    Returns a list which corresponds to the process Pid.

  Warning:

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.
> pid_to_list(whereis(init)).
"<0.0.0>"

Failure: badarg if the argument is not a Pid.

port_close(Port)

    Closes an open port. Roughly the same as Port ! {self(), close} except for the error behaviour (see below), and that the port does not reply with {Port, closed}. Any process may close a port with port_close/1, not only the port owner (the connected process).

    Returns: true.

    Failure: badarg if Port is not an open port or the registered name of an open port.

    For comparison: Port ! {self(), close} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port nothing happens. If Port is an open port and the current process is the port owner the port replies with {Port, closed} when all buffers have been flushed and the port really closes, but if the current process is not the port owner the port owner fails with badsig.

    Note that any process can close a port using Port ! {PortOwner, close} just as if it itself was the port owner, but the reply always goes to the port owner.

    In short: port_close(Port) has a cleaner and more logical behaviour than Port ! {self(), close}.

port_command(Port, Data)

    Sends data to a port. Same as Port ! {self(), {command, Data}} except for the error behaviour (see below). Any process may send data to a port with port_command/2, not only the port owner (the connected process).

    Returns: true.

    Failure: badarg if Port is not an open port or the registered name of an open port, or if Data is not an I/O list. An I/O list is a binary or a (possibly) deep list of binaries or integers in the range 0 through 255.

    For comparison: Port ! {self(), {command, Data}} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port the data message disappears without a sound. If Port is open and the current process is not the port owner, the port owner fails with badsig. The port owner fails withbadsig also if Data is not a legal I/O list.

    Note that any process can send to a port using Port ! {PortOwner, {command, Data}} just as if it itself was the port owner.

    In short: port_command(Port, Data) has a cleaner and more logical behaviour than Port ! {self(), {command, Data}}.

port_connect(Port, Pid)

    Sets the port owner (the connected port) to Pid. Roughly the same as Port ! {self(), {connect, Pid}} except for the following:

        *   The error behavior differs, see below.

        *   The port does not reply with {Port, connected}.

        *   The new port owner gets linked to the port.

    The old port owner stays linked to the port and have to call unlink(Port) if this is not desired. Any process may set the port owner to be any process with port_connect/2.

    Returns: true.

    Failure: badarg if Port is not an open port or the registered name of a port, or if Pid is not a valid local pid.

    For comparison: Port ! {self(), {connect, Pid}} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port nothing happens. If Port is an open port and the current process is the port owner the port replies with {Port, connected} to the old port owner. Note that the old port owner is still linked to the port, and that the new is not. If Port is an open port and the current process is not the port owner the port owner fails with badsig. The port owner fails with badsig also if Pid is not a valid local pid.

    Note that any process can set the port owner using Port ! {PortOwner, {connect, Pid}} just as if it itself was the port owner, but the reply always goes to the port owner.

    In short: port_connect(Port, Pid) has a cleaner and more logical behaviour than Port ! {self(), {connect, Pid}}.

port_control(Port, Operation, Data)

    Performs a synchronous control operation on a port. The meaning of Operation and Data depends on the port, i.e., on the port driver. Not all port drivers support this control feature.

    Returns: a list of integers in the range 0 through 255, or a binary, depending on the port driver. The meaning of the returned data also depends on the port driver.

    Failure: badarg if Port is not an open port or the registered name of a port, if Operation cannot fit in a 32-bit integer, if the port driver does not support synchronous control operations, if Data is not a valid I/O list (see port_command/2), or if the port driver so decides for any reason (probably something wrong with Operation or Data).

port_call(Port, Operation, Data)

    Performs a synchronous call to a port. The meaning of Operation and Data depends on the port, i.e., on the port driver. Not all port drivers support this feature.

    Port is an erlang port, referring to a driver.

    Operation is an integer, which is passed on to the driver.

    Data is any erlang term. This data is converted to binary term format and send to the port.

    Returns: a term from the driver. The meaning of the returned data also depends on the port driver.

    Failure: badarg if Port is not an open port or the registered name of a port, if Operation cannot fit in a 32-bit integer, if the port driver does not support synchronous control operations, or if the port driver so decides for any reason (probably something wrong with Operation or Data).

erlang:port_info(Port, Item)

    Returns information about the port Port as specified by Item, which can be any one of the atoms registered_name, id, connected, links, name, input, or output.

        {registered_name, Atom}:
            Atom is the registered name of the port. If the port has no registered name, this tuple is not present in the list.

        {id, Index}:
            Index is the internal index of the port. This index may be used to separate ports.

        {connected, Pid}:
            Pid is the process connected to the port.

        {links, ListOfPids}:
            ListOfPids is a list of Pids with processes to which the port has a link.

        {name, String}:
            String is the command name set by open_port.

        {input, Bytes}:
            Bytes is the total number of bytes read from the port.

        {output, Bytes}:
            Bytes is the total number of bytes written to the port.

    All implementations may not support all of the above Items. Returns undefined if the port does not exist.

    Failure: badarg if Port is not a process identifier, or if Port is a port identifier of a remote process.

erlang:port_to_list(Port)

    Returns a list which corresponds to the port identifier Port.

  Warning:

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.
> erlang:port_to_list(open_port({spawn,ls}, [])).
"#Port<0.15>"

Failure: badarg if the argument is not a port.

erlang:ports()

    Returns a list of all ports on the current node.

erlang:pre_loaded()

    Returns a list of Erlang modules which are pre-loaded in the system. As all loading of code is done through the file system, the file system must have been loaded previously. Hence, at least the module init must be pre-loaded.

erlang:process_display(Pid, Type)

    Writes information about the local process Pid on standard error. The currently allowed value for the atom Type is backtrace, which shows the contents of the stack, including information about the call chain, with the most recent data printed last. The format of the output is not further defined.

process_flag(Flag, Option)

    Sets certain flags for the process which calls this function. Returns the old value of the flag.

        process_flag(trap_exit, Boolean):
            When trap_exit is set to true, EXIT signals arriving to a process are converted to {'EXIT', From, Reason} messages, which can be received as ordinary messages. If trap_exit is set to false, the process exits if it receives an EXIT signal other than normal and the EXIT signal is propagated to its linked processes. Application processes should normally not trap exits.

        process_flag(error_handler, Module):
            This is used by a process to redefine the error handler for undefined function calls and undefined registered processes. Inexperienced users should not use this flag since code autoloading is dependent on the correct operation of the error handling module.

        process_flag(priority, Level):
            This sets the process priority. Level is an atom. All implementations support three priority levels, low, normal, and high. The default is normal.

        process_flag(save_calls, N):
            N must be an integer in the interval [0, 10000]. If N > 0, call saving is made active for the process, which means that information about the N most recent global function calls, BIF calls, sends and receives made by the process are saved in a list, which can be retrieved with process_info(Pid, last_calls). A global function call is one in which the module of the function is explicitly mentioned. Only a fixed amount of information is saved: a tuple {Module, Function, Arity} for function calls, and the mere atoms send, 'receive' and timeout for sends and receives ('receive' when a message is received and timeout when a receive times out). If N = 0, call saving is disabled for the process, which is the default. Whenever the size of the call saving list is set, its contents are reset.

    Failure: badarg if Flag is not an atom, or is not a recognized flag value, or if Option is not a recognized term for Flag.

process_flag(Pid, Flag, Option)

    Sets certain flags for the process Pid, in the same manner as process_flag/2. Returns the old value of the flag. The allowed values for Flag are only a subset of those allowed in process_flag/2, namely: save_calls.

    Failure: badarg if Pid is not a process on the local node, or if Flag is not an atom, or is not a recognized flag value, or if Option is not a recognized term for Flag.

process_info(Pid)

    Returns a long list which contains information about the process Pid. This BIF is only intended for debugging. It should not be used for any other purpose. The list returned contains the following tuples. The order in which these tuples are returned is not defined, nor are all the tuples mandatory.

        {current_function, {Module, Function, Arguments}}:
            Module, Function, Arguments is the current function call of the process.

        {dictionary, Dictionary}:
            Dictionary is the dictionary of the process.

        {error_handler, Module}:
            Module is the error handler module used by the process (for undefined function calls, for example).

        {group_leader, Groupleader}:
            Groupleader is group leader for the I/O of the process.

        {heap_size, Size}:
            Size is the heap size of the process in heap words.

        {initial_call, {Module, Function, Arity}}:
            Module, Function, Arity is the initial function call with which the process was spawned.

        {links, ListOfPids}:
            ListOfPids is a list of Pids, with processes to which the process has a link.

        {message_queue_len, MessageQueueLen}:
            MessageQueueLen is the number of messages currently in the message queue of the process. This is the length of the list MessageQueue returned as the info item messages (see below).

        {messages, MessageQueue}:
            MessageQueue is a list of the messages to the process, which have not yet been processed.

        {priority, Level}:
            Level is the current priority level for the process. Only low and normal are always supported.

        {reductions, Number}:
            Number is the number of reductions executed by the process.

        {registered_name, Atom}:
            Atom is the registered name of the process. If the process has no registered name, this tuple is not present in the list.

        {stack_size, Size}:
            Size is the stack size of the process in stack words.

        {status, Status}:
            Status is the status of the process. Status is waiting (waiting for a message), running, runnable (ready to run, but another process is running), or suspended (suspended on a "busy" port or by the erlang:suspend_process/1 BIF).

        {trap_exit, Boolean}:
            Boolean is true if the process is trapping exits, otherwise it is false.

    Failure: badarg if the argument is not a Pid, or if Pid is a Pid of a remote process.

process_info(Pid, Item)

    Returns information about the process Pid as specified by Item, in the form {Item, Info}. Item can be any one of the atoms backtrace, current_function, dictionary, error_handler, group_leader, heap_size, initial_call, last_calls, links, memory, message_queue_len, messages, monitored_by, monitors, priority, reductions, registered_name, stack_size, status or trap_exit.

    Returns undefined if no information is known about the process.

    Item registered_name returns [] if the process has no registered name.

    Item memory returns {memory, Size}, where Size is the size of the process in bytes. This includes stack, heap and internal structures.

    Item backtrace returns a binary, which contains the same information as the output from erlang:process_display(Pid, backtrace). Use binary_to_list/1 to obtain the string of characters from the binary.

    Item last_calls returns false if call saving is not active for the process (see process_flag/3). If call saving is active, a list is returned, in which the last element is the most recent.

    Item links returns a list of pids to which the process is linked.

    Item monitors returns a list of monitors (started by erlang:monitor/2) that are active for the process. For a local process monitor or a remote process monitor by pid, the list item is {process, Pid}, and for a remote process monitor by name the list item is {process, {Name, Node}}.

    Item monitored_by returns a list of pids that are monitoring the process (with erlang:monitor/2).

    Not all implementations support every one of the above Items.

    Failure: badarg if Pid is not a process identifier, or if Pid is a process identifier of a remote process.

processes()

    Returns a list of all processes on the current node.
    > processes().
    [<0.0.1>, <0.1.1>, <0.2.1>, <0.3.1>, <0.4.1>, <0.6.1>]

erlang:purge_module(Module)

    Removes old code for Module. Before this BIF is used, erlang:check_process_code/2 should be called to check that no processes are executing old code in this module.

  Warning:

In normal Erlang implementations, code handling - which is loading, deleting and replacing modules - is evaluated by the module code. This BIF is intended to be used by the implementation of the module code and should not be used in any other place.

This is an optional BIF.

Failure: badarg if Module does not exist.

put(Key, Value)

    Adds a new Value to the process dictionary and associates it with Key. If a value is already associated with Key, that value is deleted and replaced by the new value Value. It returns any value previously associated with Key, or undefined if no value was associated with Key. Key and Value can be any valid Erlang terms.

  Note:

The values stored when put is evaluated within the scope of a catch will not be retracted if a throw is evaluated, or if an error occurs.
> X = put(name, walrus), Y = put(name, carpenter),
  Z = get(name),
  {X, Y, Z}.
{undefined, walrus, carpenter}

erlang:read_timer(Ref)

    returns_timer(Ref) returns the number of milliseconds remaining for a timer, where Ref was returned by either send_after/3 or start_timer/3. If the timer was active, read_timer/1 returns the time in milliseconds left until the timer will expire, otherwise false (which may mean that Ref was never a timer, or that it has been cancelled, or that it has already delivered its message).

    Failure: badarg if Ref is not a reference.

erlang:ref_to_list(Ref)

    Returns a list which corresponds to the reference Ref.

  Warning:

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.
> erlang:ref_to_list(make_ref()).
"#Ref<0.0.0.134>"

Failure: badarg if the argument is not a reference.

register(Name, P)

    Associates the name Name with the port or process identity P. Name, which must be an atom, can be used instead of a port or pid in the send operator (Name ! Message).

    Returns true.

    Failure: badarg if P is not an active port or process, or if P is on another node, or if the name Name is already in use, or if the port or process is already registered (it already has a name), or if the name Name is not an atom, or if Name is the atom undefined.

registered()

    Returns a list of names which have been registered using register/2.
    > registered().
    [code_server, file_server, init, user, my_db]

erlang:resume_process(Pid)

    Resume a suspended process. This should be used for debugging purposes only, not in production code.

round(Number)

    Returns an integer by rounding the number Number. Allowed in guard tests.
    > round(5.5).
    6

    Failure: badarg if the argument is not a float (or an integer).

self()

    Returns the process identity of the calling process. Allowed in guard tests.
    > self().
    <0.16.1>

erlang:send(Dest, Msg)

    Sends a message and returns Msg. This is the same as Dest ! Msg.

    Dest may be a remote or local pid(), a (local) port(), a locally registered name, or a tuple {Name, Node} for a registered name on another node.

erlang:send(Dest, Msg, Options)

    Sends a message and returns ok, or does not send the message but returns something else (see below). Otherwise the same as send/2. See also send_nosuspend/2, 3 for deeper explanation and warnings.

    Options is a list of options. The possible options are:

        nosuspend:
            If the sender would have to be suspended to do the send, nosuspend is returned instead.

        noconnect:
            If the destination node would have to be autoconnected before doing the send, noconnect is returned instead.

    As with send_nosuspend/2, 3: Use with extreme care!

erlang:send_after(Time, Pid, Msg)

    Time is a non-negative integer, Pid is either a pid or an atom, and Msg is any Erlang term. The function returns a reference.

    After Time ms, send_after/3 sends Msg to Pid.

    If Pid is an atom, it is supposed to be the name of a registered process. The process referred to by the name is looked up at the time of delivery. No error is given if the name does not refer to a process. See also start_timer/3 and cancel_timer/1.

    Limitations: Pid must be a process on the local node. The timeout value must fit in 32 bits.

    Failure: badarg if any arguments are of the wrong type, or do not obey the limitations noted above.

erlang:send_nosuspend(Dest, Msg)

    The same as send(Dest, Msg, [nosuspend), but returns true if the message was sent and false if the message was not sent because the sender would have been suspended.

    This function is intended for send operations towards an unreliable remote node without ever blocking the sending (Erlang) process. If the connection to the remote node (usually not a real Erlang node, but a node written in C or Java) is overloaded, this function will not send the message but return false instead.

    The same happens, if Dest refers to a local port that is busy. For all other destinations (allowed for the ordinary send operator '!') this function sends the message and returns true.

    This function is only to be used in very rare circumstances where a process communicates with Erlang nodes that can disappear without any trace causing the TCP buffers and the drivers que to be overfull before the node will actually be shut down (due to tick timeouts) by net_kernel. The normal reaction to take when this happens is some kind of premature shutdown of the other node.

    Note that ignoring the return value from this function would result in unreliable message passing, which is contradictory to the Erlang programming model. The message is not sent if this function returns false.

    Note also that in many systems, transient states of overloaded queues are normal. The fact that this function returns false does not in any way mean that the other node is guaranteed to be nonrespoinsive, it could be a temporary overload. Also a return value of true does only mean that the message could be sent on the (TCP) channel without blocking, the message is not guaranteed to have arrived at the remote node. Also in the case of a disconnected nonresponsive node, the return value is true (mimics the behaviour of the ! operator). The expected behaviour as well as the actions to take when the function returns false are application and hardware specific.

    Use with extreme care!

erlang:send_nosuspend(Dest, Msg, Options)

    The same as send(Dest, Msg, [nosuspend | Options]), but with boolean return value.

    This function behaves like send_nosuspend/2, but takes a third parameter, a list() of options. The only currently implemented option is noconnect. The option noconnect makes the function return false if the remote node is not currently reachable by the local Erlang node. The normal behaviour is to try to connect to the node, which may stall the process for a shorter period. The use of the noconnect option makes it possible to be absolutely sure not to get even the slightest delay when sending to a remote process. This is especially useful when communicating with nodes who expect to always be the connecting part (i.e. nodes written in C or Java).

    Whenever the function returns false (either when a suspend would occur or when noconnect was specified and the node wasn't already connected), the message is guaranteed not to have been sent.

    Use with extreme care!

erlang:set_cookie(Node, Cookie)

    Sets the "magic cookie" of Node to the atom Cookie. If Node is the current node, the BIF also sets the cookie of all other unknown nodes to Cookie (see auth(3)).

setelement(Index, Tuple, Value)

    Returns a tuple which is a copy of the argument Tuple with the element given by the integer argument Index (the first element is the element with index 1) replaced by the argument Value.
    > setelement(2, {10, green, bottles}, red).
    {10, red, bottles}

    Failure: badarg if Index is not an integer, or Tuple is not a tuple, or if Index is less than 1 or greater than the size of Tuple.

size(Item)

    Returns an integer which is the size of the argument Item, where Item must be either a tuple or a binary.
    > size({morni, mulle, bwange}).
    3

    Allowed in guard tests.

    Failure: badarg if Item is not a tuple or a binary.

spawn(Fun)

    Returns the Pid of a new process started by the application of Fun to the empty argument list []. Otherwise works like spawn/3.

spawn(Node, Fun)

    Returns the Pid of a new process started by the application of Fun to the empty argument list [] on node Node. Otherwise works like spawn/4.

spawn(Module, Function, ArgumentList)

    Returns the Pid of a new process started by the application of Module:Function to ArgumentList. Note: The new process created will be placed in the system scheduler queue and will be run some time later.

    error_handler:undefined_function(Module, Function, ArgumentList) is evaluated by the new process if Module:Function/Arity does not exist (where Arity is the length of ArgumentList). The error handler can be redefined (see BIF process_flag/2)). Arity is the length of the ArgumentList. If error_handler is undefined, or the user has redefined the default error_handler so its replacement is undefined, a failure with the reason undef will occur.
    > spawn(speed, regulator, [high_speed, thin_cut]).
    <0.13.1>

    Failure: badarg if Module and/or Function is not an atom, or if ArgumentList is not a list.

spawn(Node, Module, Function, ArgumentList)

    Works like spawn/3, with the exception that the process is spawned at Node. If Node does not exist, a useless Pid is returned.

    Failure: badarg if Node, Module, or Function are not atoms, or ArgumentList is not a list.

spawn_link(Fun)

    Works like spawn/1 except that a link is made from the current process to the newly created one, atomically.

spawn_link(Node, Fun)

    Works like spawn/2 except that a link is made from the current process to the newly created one, atomically.

    Returns the Pid of the newly created process.

    Failure: See spawn/3.

spawn_link(Module, Function, ArgumentList)

    This BIF is identical to the following code being evaluated in an atomic operation:
    > Pid = spawn(Module, Function, ArgumentList),
      link(Pid),
      Pid.

    This BIF is necessary since the process created might run immediately and fail before link/1 is called.

    Returns the Pid of the newly created process.

    Failure: See spawn/3.

spawn_link(Node, Module, Function, ArgumentList)

    Works like spawn_link/3, except that the process is spawned at Node. If an attempt is made to spawn a process on a node which does not exist, a useless Pid is returned, and an EXIT signal will be received.

spawn_opt(Fun, Options)

    Returns the Pid of a new process started by the application of Fun to the empty argument list []. Otherwise works like spawn_opt/4.

spawn_opt(Node, Fun, Options)

    Returns the Pid of a new process started by the application of Fun to the empty argument list []. Otherwise works like spawn_opt/5.

spawn_opt(Module, Function, ArgumentList, Options)

    Works exactly like spawn/3, except that an extra option list can be given when creating the process.

  Warning:

This BIF is only useful for performance tuning. Random tweaking of the parameters without measuring execution times and memory consumption may actually make things worse. Furthermore, most of the options are inherently implementation-dependent, and they can be changed or removed in future versions of OTP.

    link:
        Sets a link to the parent process (like spawn_link/3 does).

    {priority, Level}:
        Sets the priority of the new process. Equivalent to executing process_flag(priority, Level) in the start function of the new process, except that the priority will be set before the process is scheduled in the first time.

    {fullsweep_after, Number}:
        The Erlang runtime system uses a generational garbage collection scheme, using an "old heap" for data that has survived at least one garbage collection. When there is no more room on the old heap, a fullsweep garbage collection will be done.

        Using the fullsweep_after option, you can specify the maximum number of generational collections before forcing a fullsweep even if there is still room on the old heap. Setting the number to zero effectively disables the general collection algorithm, meaning that all live data is copied at every garbage collection.

        Here are a few cases when it could be useful to change fullsweep_after. Firstly, if you want binaries that are no longer used to be thrown away as soon as possible. (Set Number to zero.) Secondly, a process that mostly have short-lived data will be fullsweeped seldom or never, meaning that the old heap will contain mostly garbage. To ensure a fullsweep once in a while, set Number to a suitable value such as 10 or 20. Thirdly, in embedded systems with limited amount of RAM and no virtual memory, you might want to preserve memory by setting Number to zero. (You probably want to the set the value globally. See system_flag/2.)

    {min_heap_size, Size}:
        Gives a minimum heap size in words. Setting this value higher than the system default might speed up some processes because less garbage collection is done. Setting too high value, however, might waste memory and slow down the system due to worse data locality. Therefore, it is recommended to use this option only for fine-tuning an application and to measure the execution time with various Size values.

spawn_opt(Node, Module, Function, ArgumentList, Options)

    Works like spawn_opt/4, except that the process is spawned at Node. If an attempt is made to spawn a process on a node which does not exist, a useless Pid is returned, and an EXIT signal will be received.

split_binary(Binary, Pos)

    Returns a tuple which contains two binaries which are the result of splitting Binary into two parts at position Pos. This is not a destructive operation. After this operation, there are three binaries altogether. Returns a tuple consisting of the two new binaries. For example:
    1> B = list_to_binary("0123456789").
    #Bin
    2> size(B).
    10
    3> {B1, B2} = split_binary(B,3).
    {#Bin, #Bin}
    4> size(B1).
    3
    5> size(B2).
    7

    Failure: badarg if Binary is not a binary, or Pos is not an integer or is out of range.

erlang:start_timer(Time, Pid, Msg)

    Time is a non-negative integer, Pid is either a pid or an atom, and Msg is any Erlang term. The function returns a reference.

    After Time ms, start_timer/3 sends the tuple {timeout, Ref, Msg} to Pid, where Ref is the reference returned by start_timer/3.

    If Pid is an atom, it is supposed to be the name of a registered process. The process referred to by the name is looked up at the time of delivery. No error is given if the name does not refer to a process. See also send_after/3 and cancel_timer/1.

    Limitations: Pid must be a process on the local node. The timeout value must fit in 32 bits.

    Failure: badarg if any arguments are of the wrong type, or do not obey the limitations noted above.

statistics(Type)

    Returns information about the system. Type is an atom which is one of:

        run_queue:
            Returns the length of the run queue, that is the number of processes that are ready to run.

        runtime:
            Returns {Total_Run_Time, Time_Since_Last_Call}.

        wall_clock:
            Returns {Total_Wallclock_Time, Wallclock_Time_Since_Last_Call}. wall_clock can be used in the same manner as the atom runtime, except that real time is measured as opposed to runtime or CPU time.

        reductions:
            Returns {Total_Reductions, Reductions_Since_Last_Call}.

        garbage_collection:
            Returns {Number_of_GCs, Words_Reclaimed, 0}. This information may not be valid for all implementations.

    All times are in milliseconds.
    > statistics(runtime).
    {1690, 1620}
    > statistics(reductions).
    {2046, 11}
    > statistics(garbage_collection).
    {85, 23961, 0}

    Failure: badarg if Type is not one of the atoms shown above.

erlang:suspend_process(Pid)

    Suspend a process. This should be used for debugging purposes only, not in production code.

erlang:system_flag(Flag, Value)

    This BIF sets various system properties of the Erlang node. If Flag is a valid name of a system flag, its value is set to Value, and the old value is returned.

    The following values for Flag are currently allowed: fullsweep_after and backtrace_depth.

    The value of the fullsweep_after is an non-negative integer which indicates how many times generational garbages collections can be done without forcing a fullsweep collection. The value applies to new processes; processes already running are not affected.

    In low-memory systems (especially without virtual memory), setting the value to zero can help to conserve memory.

    An alternative way to set this value is through the (operating system) environment variable ERL_FULLSWEEP_AFTER.

erlang:system_info(What)

    What can be any of the atoms info, procs, loaded, dist, thread_pool_size, allocated_areas, allocator, {allocator, Alloc}, system_version or system_architecture. The BIF returns information of the different `topics' as binary data objects (except for thread_pool_size, allocated_areas, and allocator, {allocator, Alloc} see below).

        erlang:system_info(thread_pool_size):
            Returns the number of threads used for driver calls (as an integer).

        erlang:system_info(allocated_areas):
            Information about miscellaneous allocated memory areas.
             A list of tuples is returned. Each tuple contains an atom describing type of memory as first element and amount of allocated memory in bytes as second element. In those cases when there is information present about allocated and used memory, a third element is present. This third element contains the amount of used memory in bytes.
             erlang:system_info(allocated_areas) is intended for debugging, and the content is highly implementation dependent. The content of the results will therefore change when needed without prior notice.
             NOTE: The sum of these values is not the total amount of memory allocated by the emulator. Some values are part of other values, and some memory areas are not part of the result. If you are interested in the total amount of memory allocated by the emulator see erlang:memory/0 or erlang:memory/1.

        erlang:system_info(allocator):
            Returns {Allocator, Version, Features, Settings}.

            Types:

                *   Allocator = atom()

                *   Version = [int()]

                *   Features = [atom()]

                *   Settings = [{Subsystem, [{Parameter, Value}]}]

                *   Subsystem = atom()

                *   Parameter = atom()

                *   Value = term()

            Explanation:

                *   Allocator corresponds to the malloc() implementation used. If Allocator equals undefined, the malloc() implementation used couldn't be identified. Currently elib_malloc, and glibc can be identified.

                *   Version is a list of integers (but not a string) representing the version of the malloc() implementation used.

                *   Features is a list of atoms representing allocation features used.

                *   Settings is a list of subsystems, their configurable parameters, and used values. Settings may differ between different combinations of platforms, allocators, and allocation features. Memory sizes are given in bytes.

             See also "System Flags Effecting erts_alloc" section in the erts_alloc(3) man page.

        erlang:system_info({allocator, Alloc}):
            Types:

                *   Alloc = atom()

            Returns information about the Alloc allocator. If Alloc is not a recognised allocator, undefined is returned. If Alloc is disabled, false is returned.

            NOTE: The information returned is highly implementation dependent and may be changed, or removed at any time without prior notice. It was initially intended as a tool when developing new allocators, but since it might be of interest for others it has been briefly documented.

            The returned information more or less speaks for itself once you have read the erts_alloc(3) man page, but it can be worth explaining some things. Call counts are presented by two values. The first value is giga calls, and the second value is calls. mbcs, and sbcs are abbreviations for, respectively, multiblock carriers, and singleblock carriers. Sizes are presented in bytes. When it's not a size that is presented, it's the amount of something. Sizes and amounts are often presented by three values, the first is current value, the second is maximum value since the last call to erlang:system_info({allocator, Alloc}), and the third is maximum value since the emulator was started. If only one value is present, it's the current value. fix_alloc memory block types are presented by two values. The first value is memory pool size and the second value used memory size.

        erlang:system_info(system_version):
            Returns a string containing the emulator type and version as well as some important properties such as the size of the thread pool, etc.

        erlang:system_info(system_architecture):
            Returns a string containing the processor and OS architecture the emulator is built for.

    Failure: badarg if What is not one of the atoms shown above.

erlang:system_monitor(MonitorPid, Options)

    Sets system performance monitoring options. MonitorPid is a node-local pid() that will receive system monitor messages, and Options is a list of monitoring options:

        {long_gc, Time}:
            If a garbage collection in the system takes at least Time wallclock milliseconds, a message {monitor, GcPid, long_gc, Info} is sent to MonitorPid. GcPid is the pid() that was garbage collected and Info is a list of two-element tuples describing the result of the garbage collection. One of the tuples is {timeout, GcTime} where GcTime is the actual time for the garbage collection in milliseconds. The other are the tuples tagged with heap_size, stack_size, mbuf_size and heap_block_size from the gc_start trace message (see erlang:trace/3).

        {large_heap, Size}:
            If a garbage collection in the system results in the allocated size of a heap being at least Size words, a message {monitor, GcPid, large_heap, Info} is sent to MonitorPid. GcPid and Info are the same as for long_gc above, except that the tuple tagged with timeout is not present.

        busy_port:
            If a process in the system gets suspended because it sends to a busy port, a message {monitor, SusPid, busy_port, Port} is sent to MonitorPid. SusPid is the pid() that got suspended when sending to Port.

        busy_dist_port:
            If a process in the system gets suspended because it sends to a process on a remote node whose inter-node communication was handled by a busy port, a message {monitor, SusPid, busy_port, Port} is sent to MonitorPid. SusPid is the pid() that got suspended when sending through the inter-node communication port Port.

    Returns the previous system monitor settings just like erlang:system_monitor/0.

  Note:

If a monitoring process gets so large that it itself starts to cause system monitor messages when garbage collecting, the messages will enlargen the process's message queue and probably make the problem worse.

Keep the monitoring process neat and do not set the system monitor limits too tight.

erlang:system_monitor({MonitorPid, Options})

    The same as erlang:system_monitor(MonitorPid, Options).

erlang:system_monitor(undefined)

    Clears all system monitoring set by erlang:system_monitor/2.

    Returns the previous system monitor settings just like erlang:system_monitor/0.

erlang:system_monitor()

    Returns the current system monitoring settings set by erlang:system_monitor/2 as {MonitorPid, Options}. The order of the options may be different from the one that was set.

term_to_binary(Term)

    This BIF returns the encoded value of any Erlang term and turns it into the Erlang external term format. It can be used for a variety of purposes, for example writing a term to a file in an efficient way, or sending an Erlang term to some type of communications channel not supported by distributed Erlang.

    Returns a binary data object which corresponds to an external representation of the Erlang term Term.

term_to_binary(Term, Options)

    This BIF returns the encoded value of any Erlang term and turns it into the Erlang external term format. If the Options list contains the atom compressed, the external term format will be compressed. The compressed format is automatically recognized by binary_to_term/1 in R7.

    Returns a binary data object which corresponds to an external representation of the Erlang term Term.

    Failure: badarg if Options is not a list or if contains something else than the supported flags (currently only the atom compressed).

throw(Any)

    A non-local return from a function. If evaluated within a catch, catch will return the value Any.
    > catch throw({hello, there}).
    {hello, there}

    Failure: nocatch if not evaluated within a catch.

time()

    Returns the tuple {Hour, Minute, Second} of the current system time. The time zone correction is implementation-dependent.
    > time().
    {9, 42, 44}

tl(List)

    Returns List stripped of its first element.
    > tl([geesties, guilies, beasties]).
    [guilies, beasties]

    Failure: badarg if List is the empty list [], or is not a list. Allowed in guard tests.

erlang:trace(PidSpec, How, Flaglist)

    Turns on (if How == true) or off (if How == false) the trace flags in Flaglist for the process or processes represented by PidSpec. PidSpec is either a pid for a local process, or one of the following atoms:

        existing:
            All processes currently existing.

        new:
            All processes that will be created in the future.

        all:
            All currently existing processes and all processes that will be created in the future.

    Flaglist can contain any number of the following atoms (the "message tags" refers to the list of messages following below):

        all:
            All trace flags except {tracer, Tracer} and cpu_timestamp that are in their nature different than the others.

        send:
            Traces the messages the process Pid sends. Message tags: send, send_to_non_existing_process.

        'receive':
            Traces the messages the process Pid receives. Message tags: 'receive'.

        procs:
            Traces process related events, for example spawn, link, exit. Message tags: spawn, exit, register, unregister, link, unlink, getting_linked, getting_unlinked.

        call:
            Traces function calls to functions that tracing has been enabled for. Use the erlang:trace_pattern/3 BIF to enable tracing for functions. Message tags: call, return_from.

        silent:
            To be used in conjunction with the call trace flag. Sets the call trace message mode for the process Pid to silent, i.e, the call tracing is active, match specs are executed as normal, but no call trace messages are generated.

            The silent mode can, of course, be inhibited by executing erlang:trace/3 without the silent flag, but also by a match spec executing the {silent, false} function.

        return_to:
            Traces the actual return of a process from a traced function back to its caller. This return trace only works together with call trace and functions traced with the local option to erlang:trace_pattern/3 . The semantics is that a message is sent when a call traced function actually returns, i.e., when a chain of tail recursive calls is ended. There will be only one trace message sent per chain of tail recursive calls, why the properties of tail recursiveness for function calls are kept while tracing with this flag. Using call and return_to trace together makes it possible to know exactly in which function a process executes at any time.

            To get trace messages containing return values from functions, use the {return_trace} match_spec action instead.

            Message tags: return_to.

        running:
            Traces scheduling of processes. Message tags: in, out.

        garbage_collection:
            Traces garbage collections of processes. Message tags: gc_start, gc_end.

        timestamp:
            Make a time stamp in all trace messages. The time stamp (Ts) is of the same form as returned by erlang:now().

        cpu_timestamp:
            A global trace flag for the Erlang node that makes all trace timestamps be in CPU time, not wallclock. It is only allowed with PidSpec==all. If the host machine operating system does not support high resolution CPU time measurements, trace/3 exits with badarg.

        arity:
            Instead of {Mod, Fun, Args} in call traces, there will be {Mod, Fun, Arity}.

        set_on_spawn:
            Makes any process created by Pid inherit the flags of Pid, including the set_on_spawn flag.

        set_on_first_spawn:
            Makes the first process created by Pid inherit the flags of Pid That process does not inherit the set_on_first_spawn flag.

        set_on_link:
            Makes any process linked by Pid inherit the flags of Pid, including the set_on_link flag.

        set_on_first_link:
            Makes the first process linked to by Pid inherit the flags of Pid. That process does not inherit the set_on_first_link flag.

        {tracer, Tracer}:
            Tracer should be the pid for a local process or the port identifier for a local port. All trace messages will be sent to the given process or port. If this flag is not given, trace messages will be sent to the process that called erlang:trace/3.

    The effect of combining set_on_first_link with set_on_link is the same as having set_on_first_link alone. Likewise for set_on_spawn and set_on_first_spawn.

    If the timestamp flag is not given, the tracing process will receive the trace messages described below. If the timestamp flag is given, the first element of the tuple will be trace_ts and the timestamp will be in the last element of the tuple.

        {trace, Pid, 'receive', Message}:
            When the traced Pid receives something.

        {trace, Pid, send, Msg, To}:
            When Pid sends a message.

        {trace, Pid, send_to_non_existing_process, Msg, To}:
            When Pid sends a message to a non existing process.

        {trace, Pid, call, {M, F, A}}:
            When Pid makes a function/BIF call. The return values of calls are never supplied, only the call and its arguments.

        {trace, Pid, return_to, {M, F, A}}:
            When Pid returns to function {M, F, A}. This message will be sent if both the call and the return_to flags are present and the function is set to be traced on local function calls. The message is only sent when returning from a chain of tail recursive function calls where at least one call generated a call trace message (i.e., the functions match specification matched and {message, false} was not an action).

        {trace, Pid, return_from, {M, F, A}, ReturnValue}:
            When Pid returns from the function {M, F, A} This trace message is sent when the call flag has been specified, and the function has a match specification with a return_trace action.

        {trace, Pid, spawn, Pid2, {M, F, A}}:
            When Pid spawns a new process Pid2. {M, F, A} are the initial function call with arguments for the new process.

            Note that A is supposed to be the argument list, but may be any term in the case of an erroneous spawn.

        {trace, Pid, exit, Reason}:
            When Pid exits with reason Reason.

        {trace, Pid, link, Pid2}:
            When Pid links to a process Pid2.

        {trace, Pid, unlink, Pid2}:
            When Pid removes the link from a process Pid2.

        {trace, Pid, getting_linked, Pid2}:
            When Pid gets linked to a process Pid2.

        {trace, Pid, getting_unlinked, Pid2}:
            When Pid gets unlinked from a process Pid2.

        {trace, Pid, register, Name}:
            When Pid gets the name Name registered.

        {trace, Pid, unregister, Name}:
            When Pid gets the name Name unregistered. Note that this is done automatically when a registered process exits.

        {trace, Pid, in, {M, F, A} | 0}:
            When Pid is scheduled to run. The process will run in function {M,F,A}, where A is always the arity. On some rare occasions the current function cannot be determined, then the last element is 0.

        {trace, Pid, out, {M, F, A} | 0}:
            When Pid is scheduled out. The process was running in function {M,F,A} where A is always the arity. On some rare occasions the current function cannot be determined, then the last element is 0.

        {trace, Pid, gc_start, Info}:
            Sent when garbage collection is about to be started. Info is a list of two-element tuples, where the first element is a key, and the second is the value. You should not depend on the tuples have any defined order Currently, the following keys are defined.

                heap_size:
                    The size of the used part of the heap.

                old_heap_size:
                    The size of the used part of the old heap.

                stack_size:
                    The actual size of the stack.

                recent_size:
                    The size of the data that survived the previous garbage collection.

                mbuf_size:
                    The combined size of message buffers associated with the process.

            All sizes are in words.

        {trace, Pid, gc_end, Info}:
            Sent when garbage collection is finished. Info contains the same kind of list as in the gc_start message, but the sizes reflect the new sizes after garbage collection.

    If the tracing process dies, the flags will be silently removed.

    Only one process can trace a particular process. For this reason, attempts to trace an already traced process will fail.

    Returns: A number indicating the number of processes that matched PidSpec. If PidSped is a pid, the return value will be 1. If PidSpec is all or existing the return value will be the number of processes running, excluding tracer processes. If PidSpec is new, the return value will be 0.

    Failure: badarg if bad arguments are given. Or if arguments are not supported, for example cpu_timestamp is not supported on all platforms.

erlang:trace_info(PidOrFunc, Item)

    Returns trace information about a process or function.

    To get information about a process, PidOrFunc should be a pid or the atom new. The atom new means that the default trace state for processes to be created will be returned. Item must have one of the following values:

        flags:
            Return a list of atoms indicating what kind of traces is enabled for the process. The list will be empty if no traces are enabled, and one or more of the followings atoms if traces are enabled: send, 'receive', set_on_spawn, call, return_to, procs, set_on_first_spawn, set_on_link, running, garbage_collection, timestamp, and arity. The order is arbitrary.

        tracer:
            Return the identifier for process or port tracing this process. If this process is not being traced, the return value will be [].

    To get information about a function, PidOrFunc should be a three-element tuple: {Module, Function, Arity} or the atom on_load. No wildcards are allowed. Return undefined if the function does not exist and false if the function is not traced at all. Item must have one of the following values:

        traced:
            Return global if this function is traced on global function calls, local if this function is traced on local function calls (i.e local and global function calls), and false if neither local nor global function calls are traced.

        match_spec:
            Return the match specification for this function, if it has one. If the function is locally or globally traced but has no match specification defined, the returned value is [].

        meta:
            Return the meta trace tracer process or port for this function, if it has one. If the function is not meta traced the returned value is false, and if the function is meta traced but has once detected that the tracer proc is invalid, the returned value is [].

        meta_match_spec:
            Return the meta trace match specification for this function, if it has one. If the function is meta traced but has no match specification defined, the returned value is [].

        call_count:
            Return the call count value for this function or true for the pseudo function on_loadif call count tracing is active. Return false otherwise. See also erlang:trace_pattern/3 .

        all:
            Return a list contaning the {Item, Value} tuples for all other items, or return false if no tracing is active for this function.

    The actual return value will be {Item, Value}, where Value is the requested information as described above. If a pid for a dead process was given, or the name of a non-existing function, Value will be undefined.

    If PidOrFunc is the on_load, the information returned refers to the default value for code that will be loaded.

erlang:trace_pattern(MFA, MatchSpec)

    The same as erlang:trace_pattern(MFA, MatchSpec, []), retained for backward compatibility.

erlang:trace_pattern(MFA, MatchSpec, FlagList)

    This BIF is used to enable or disable call tracing for exported functions. It must be combined with erlang:trace/3 to set the call trace flag for one or more processes.

    Conceptually, call tracing works like this: Inside the Erlang virtual machine there is a set of processes to be traced and a set of functions to be traced. Tracing will be enabled on the intersection of the set. That is, if a process included in the traced process set calls a function included in the traced function set, the trace action will be taken. Otherwise, nothing will happen.

    Use erlang:trace/3 to add or remove one or more processes to the set of traced processes. Use erlang:trace_pattern/2 to add or remove exported functions to the set of traced functions.

    The erlang:trace_pattern/3 BIF can also add match specifications to an exported function. A match specification comprises a pattern that the arguments to the function must match, a guard expression which must evaluate to true and action to be performed. The default action is to send a trace message. If the pattern does not match or the guard fails, the action will not be executed.

    The MFA argument should be a tuple like {Module, Function, Arity} or the atom on_load (described below). It can be the module, function, and arity for an exported function (or a BIF in any module). The '_' atom can be used to mean any of that kind. Wildcards can be used in any of the following ways:

        {Mod, Func, '_'}:
            All exported functions of any arity named Func in module Mod.

        {Mod, '_', '_'}:
            All exported functions in module Mod.

        {'_', '_', '_'}:
            All exported functions in all loaded modules.

    Other combinations, such as {Mod, '_', Arity}, are not allowed. Local functions will match wildcards only if the local option is in the FlagList.

    If the MFA argument is the atom on_load, the match specification and flag list will be used on all modules that are newly loaded.

    The MatchSpec argument can take any of the following forms:

        false:
            Disable tracing for the matching function(s). Any match specification will be removed.

        true:
            Enable tracing for the matching function(s).

        MatchSpecList:
            A list of match specifications. An empty list is equivalent to true. See the ERTS User's Guide for a description of match specifications.

        restart:
            For the FlagList option call_count: restart the existing counters. The behaviour is undefined for other FlagList options.

        pause:
            For the FlagList option call_count: pause the existing counters. The behaviour is undefined for other FlagList options.

    The FlagList parameter is a list of options. The following options are allowed:

        global:
            Turn on or off call tracing for global function calls (i.e., calls specifying the module explicitly). Only exported functions will match and only global calls will generate trace messages. This is the default.

        local:
            Turn on or off call tracing for all types of function calls. Trace messages will be sent whenever any of the specified functions are called, regardless of how they are called. If the return_to flag is set for the process, a return_to message will also be sent when this function returns to its caller.

        meta | {meta, Pid}:
            Turn on or off meta tracing for all types of function calls. Trace messages will be sent to the tracer process or port Pid whenever any of the specified functions are called, regardless of how they are called. If no Pid is specified, self() is used as a default tracer process.

            Meta tracing traces all processes and does not care about the process trace flags set by trace/3, the trace flags are instead fixed to [call, timestamp].

            The match spec function {return_trace} works with meta trace and send its trace message to the same tracer process.

        call_count:
            Starts (MatchSpec == true) or stops (MatchSpec == false) call count tracing for all types of function calls. For every function a counter is incremented when the function is called, in any process. No process trace flags need to be activated.

            If call count tracing is started while already running, the count is restarted from zero. Running counters can be paused with MatchSpec == pause. Paused and running counters can be restarted from zero with MatchSpec == restart.

            The counter value can be read with erlang:trace_info/2 .

    The global and local options are mutually exclusive and global is the default (if no options are specified). The call_count and meta options perform a kind of local tracing, and can also not be combined with global. A function can be either globally or locally traced. If global tracing is specified for a specified set of functions; local, meta and call count tracing for the matching set of local functions will be disabled, and vice versa.

    When disabling trace, the option must match the type of trace that is set on the function, so that local tracing must be disabled with the local option and global tracing with the global option (or no option at all), and so forth.

    There is no way to directly change part of a match specification list. If a function has a match specification, you can replace it with a completely new one. If you need to change an existing match specification, use the erlang:trace_info/2 BIF to retrieve the existing match specification.

    Returns the number of exported functions that matched the MFA argument. This will be zero if none matched at all.

    Failure: badarg for invalid MFA or MatchSpec.

trunc(Number)

    Returns an integer by the truncation of Number. Allowed in guard tests.
    > trunc(5.5).
    5

    Failure: badarg if the argument is not a float, or an integer.

tuple_to_list(Tuple)

    Returns a list which corresponds to Tuple. Tuple may contain any valid Erlang terms.
    > tuple_to_list({share, {'Ericsson_B', 163}}).
    [share, {'Ericsson_B', 163}]

    Failure: badarg if the argument is not a tuple.

erlang:universaltime()

    Returns the current date and time according to Universal Time Coordinated (UTC), also called GMT, in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported by the underlying operating system. If not, erlang:universaltime() is equivalent to erlang:localtime().
    > erlang:universaltime().
    {{1996,11,6},{14,18,43}}

erlang:universaltime_to_localtime(DateTime)

    Converts UTC date and time in DateTime to local date and time if supported by the underlying operating system. Otherwise, no conversion is done, and DateTime is returned. The return value is of the form {{Year, Month, Day}, {Hour, Minute, Second}}.

    Failure: badarg if the argument is not a valid date and time tuple {{Year, Month, Day}, {Hour, Minute, Second}}.
    > erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
    {{1996,11,7},{15,18,43}}

unlink(Pid)

    Removes a link, if there is one, from the calling process to another process given by the argument Pid.

    Returns true. Will not fail if not linked to Pid, or if Pid does not exist.

    Failure: badarg if the argument is not a valid Pid.

unregister(Name)

    Removes the registered name for a port or process, given by the atom argument Name.

    Returns the atom true.
    > unregister(db).
    true

    Failure: badarg if Name is not the name of a registered port or process.

    Users are advised not to unregister system processes.

whereis(Name)

    Returns the identifier of the port or process registered under Name (see register/2). Returns undefined if no such port or process is registered.
    > whereis(user).
    <0.3.1>

    Failure: badarg if the argument is not an atom.

erlang:yield()

    Voluntarily let other processes (if any) get a chance to execute. Using yield() is similar to receive after 1 -> ok end, except that yield() is faster.

AUTHORS
Joe Armstrong - support@erlang.ericsson.se
Mike Williams - support@erlang.ericsson.se
Robert Virding - support@erlang.ericsson.se
Claes Wikstrom - support@erlang.ericsson.se