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#### 11.7.5 Function Locking

It is sometime desirable to lock a function into memory with the `mlock` function. This is typically used for dynamically linked functions in Oct-files or mex-files that contain some initialization, and it is desirable that calling `clear` does not remove this initialization.

As an example,

         mlock ("my_function");

prevents `my_function` from being removed from memory, even if `clear` is called. It is possible to determine if a function is locked into memory with the `mislocked`, and to unlock a function with `munlock`, which the following illustrates.

         mlock ("my_function");
         mislocked ("my_function")
          ans = 1
         munlock ("my_function");
         mislocked ("my_function")
          ans = 0

A common use of `mlock` is to prevent persistent variables from being removed from memory, as the following example shows:

         function count_calls()
           persistent calls = 0;
           printf ("'count_calls' has been called %d times\n",
                   ++calls);
         endfunction
         mlock ("count_calls");

         count_calls ();
         -| 'count_calls' has been called 1 times

         clear count_calls
         count_calls ();
         -| 'count_calls' has been called 2 times

It is, however, often inconvenient to lock a function from the prompt, so it is also possible to lock a function from within its body. This is simply done by calling `mlock` from within the function.

         function count_calls ()
           mlock ();
           persistent calls = 0;
           printf ("'count_calls' has been called %d times\n",
                   ++calls);
         endfunction

`mlock` might equally be used to prevent changes to a function from having effect in Octave, though a similar effect can be had with the `ignore_function_time_stamp` function.

— Built-in Function: mlock ()

> Lock the current function into memory so that it can't be cleared.

> See also: munlock, mislocked, persistent.

— Built-in Function: munlock (fcn)

> Unlock the named function. If no function is named then unlock the current function.

> See also: mlock, mislocked, persistent.

— Built-in Function: mislocked (fcn)

> Return true if the named function is locked. If no function is named then return true if the current function is locked.

> See also: mlock, munlock, persistent.