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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,

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 ()
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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