timer(3)

NAME
timer - Timer Functions

DESCRIPTION

This module provides useful functions related to time. Unless otherwise stated, time is always measured in milliseconds . All timer functions return immediately, regardless of work carried out by another process.

Successful evaluations of the timer functions yield return values containing a timer reference, denoted TRef below. By using cancel/1 , the returned reference can be used to cancel any requested action. A TRef is an Erlang term, the contents of which must not be altered.

The timeouts are not exact, but should be at least as long as requested.

EXPORTS

start() -> ok

    Starts the timer server. Normally, the server does not need to be started explicitly. It is started dynamically if it is needed. This is useful during development, but in a target system the server should be started explicitly. Use configuration parameters for kernel for this.

apply_after(Time, Module, Function, Arguments) -> {ok, Tref} | {error, Reason}

    Types
        Time = integer() in Milliseconds
        Module = Function = atom()
        Arguments = [term()]

    Evaluates apply(M, F, A) after Time amount of time has elapsed. Returns {ok, TRef} , or {error, Reason} .

send_after(Time, Pid, Message) -> {ok, TRef} | {error,Reason}
send_after(Time, Message) -> {ok, TRef} | {error,Reason}

    Types
        Time = integer() in Milliseconds
        Pid = pid() | atom()
        Message = term()
        Result = {ok, TRef} | {error, Reason}

        send_after/3 :
            Evaluates Pid ! Message after Time amount of time has elapsed. ( Pid can also be an atom of a registered name.) Returns {ok, TRef} , or {error, Reason} .

        send_after/2 :
            Same as send_after(Time, self(), Message) .

exit_after(Time, Pid, Reason1) -> {ok, TRef} | {error,Reason2}
exit_after(Time, Reason1) -> {ok, TRef} | {error,Reason2}
kill_after(Time, Pid)-> {ok, TRef} | {error,Reason2}
kill_after(Time) -> {ok, TRef} | {error,Reason2}

    Types
        Time = integer() in milliseconds
        Pid = pid() | atom()
        Reason1 = Reason2 = term()

        exit_after/3 :
            Send an exit signal with reason Reason1 to Pid Pid . Returns {ok, TRef} , or {error, Reason2} .

        exit_after/2 :
            Same as exit_after(Time, self(), Reason1) .

        kill_after/2 :
            Same as exit_after(Time, Pid, kill) .

        kill_after/1 :
            Same as exit_after(Time, self(), kill) .

apply_interval(Time, Module, Function, Arguments) -> {ok, TRef} | {error, Reason}

    Types
        Time = integer() in milliseconds
        Module = Function = atom()
        Arguments = [term()]

    Evaluates apply(Module, Function, Arguments) repeatedly at intervals of Time . Returns {ok, TRef} , or {error, Reason} .

send_interval(Time, Pid, Message) -> {ok, TRef} | {error, Reason}
send_interval(Time, Message) -> {ok, TRef} | {error, Reason}

    Types
        Time = integer() in milliseconds
        Pid = pid() | atom()
        Message = term()
        Reason = term()

        send_interval/3 :
            Evaluates Pid ! Message repeatedly after Time amount of time has elapsed. ( Pid can also be an atom of a registered name.) Returns {ok, TRef} or {error, Reason} .

        send_interval/2 :
            Same as send_interval(Time, self(), Message) .

cancel(TRef) -> {ok, cancel} | {error, Reason}

    Cancels a previously requested timeout. TRef is a unique timer reference returned by the timer function in question. Returns {ok, cancel} , or {error, Reason} when TRef is not a timer reference.

sleep(Time) -> ok

    Types
        Time = integer() in milliseconds or the atom infinity

    Suspends the process calling this function for Time amount of milliseconds and then returns ok , or suspend the process forever if Time is the atom infinity . Naturally, this function does not return immediately.

tc(Module, Function, Arguments) -> {Time, Value}
tc(Fun, Arguments) -> {Time, Value}

    Types
        Module = Function = atom()
        Fun = fun()
        Arguments = [term()]
        Time = integer() in microseconds
        Value = term()

        tc/3 :
            Evaluates apply(Module, Function, Arguments) and measures the elapsed real time as reported by now/0 . Returns {Time, Value} , where Time is the elapsed real time in microseconds , and Value is what is returned from the apply.

        tc/2 :
            Evaluates apply(Fun, Arguments) . Otherwise works like tc/3 .

now_diff(T2, T1) -> Tdiff

    Types
        T1 = T2 = {MegaSecs, Secs, MicroSecs}
        Tdiff = MegaSecs = Secs = MicroSecs = integer()

    Calculates the time difference Tdiff = T2 - T1 in microseconds , where T1 and T2 probably are timestamp tuples returned from erlang:now/0 .

seconds(Seconds) -> Milliseconds

    Returns the number of milliseconds in Seconds .

minutes(Minutes) -> Milliseconds

    Return the number of milliseconds in Minutes .

hours(Hours) -> Milliseconds

    Returns the number of milliseconds in Hours .

hms(Hours, Minutes, Seconds) -> Milliseconds

    Returns the number of milliseconds in Hours + Minutes + Seconds .

EXAMPLES

This example illustrates how to print out "Hello World!" in 5 seconds:

      1> timer:apply_after(5000, io, format, ["~nHello World!~n", []]).
      {ok,TRef}
      Hello World!

The following coding example illustrates a process which performs a certain action and if this action is not completed within a certain limit, then the process is killed.

      Pid = spawn(mod, fun, [foo, bar]),
      %% If pid is not finished in 10 seconds, kill him
      {ok, R} = timer:kill_after(timer:seconds(10), Pid),
      ...
      %% We change our mind...
      timer:cancel(R),
      ...

WARNING

A timer can always be removed by calling cancel/1 .

An interval timer, i.e. a timer created by evaluating any of the functions apply_interval/4 , send_interval/3 , and send_interval/2 , is linked to the process towards which the timer performs its task.

A one-shot timer, i.e. a timer created by evaluating any of the functions apply_after/4 , send_after/3 , send_after/2 , exit_after/3 , exit_after/2 , kill_after/2 , and kill_after/1 is not linked to any process. Hence, such a timer is removed only when it reaches its timeout, or if it is explicitly removed by a call to cancel/1 .