11.8.5 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.