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#### 11.9.6 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,

    function my_function ()
      mlock ();
      …

prevents `my_function` from being removed from memory after it is called, 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.

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

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

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

`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 ()
Built-in Function: munlock (fcn)

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

  See also: mlock, mislocked, persistent.

Built-in Function: mislocked ()
Built-in Function: mislocked (fcn)

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

  See also: mlock, munlock, persistent.

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