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<h4 class="subsection">11.7.5 Function Locking</h4>
<p>It is sometime desirable to lock a function into memory with the
<code>mlock</code> 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 <code>clear</code> does not remove this
initialization.
<p>As an example,
<pre class="example"> mlock ("my_function");
</pre>
<p class="noindent">prevents <code>my_function</code> from being removed from memory, even if
<code>clear</code> is called. It is possible to determine if a function is
locked into memory with the <code>mislocked</code>, and to unlock a function
with <code>munlock</code>, which the following illustrates.
<pre class="example"> mlock ("my_function");
mislocked ("my_function")
⇒ ans = 1
munlock ("my_function");
mislocked ("my_function")
⇒ ans = 0
</pre>
<p>A common use of <code>mlock</code> is to prevent persistent variables from
being removed from memory, as the following example shows:
<pre class="example"> 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
</pre>
<p class="noindent">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 <code>mlock</code> from within the function.
<pre class="example"> function count_calls ()
mlock ();
persistent calls = 0;
printf ("'count_calls' has been called %d times\n",
++calls);
endfunction
</pre>
<p><code>mlock</code> might equally be used to prevent changes to a function from having
effect in Octave, though a similar effect can be had with the
<code>ignore_function_time_stamp</code> function.
<!-- variables.cc -->
<p><a name="doc_002dmlock"></a>
<div class="defun">
— Built-in Function: <b>mlock</b> ()<var><a name="index-mlock-639"></a></var><br>
<blockquote><p>Lock the current function into memory so that it can't be cleared.
<!-- Texinfo @sp should work but in practice produces ugly results for HTML. -->
<!-- A simple blank line produces the correct behavior. -->
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dmunlock.html#doc_002dmunlock">munlock</a>, <a href="doc_002dmislocked.html#doc_002dmislocked">mislocked</a>, <a href="doc_002dpersistent.html#doc_002dpersistent">persistent</a>.
</p></blockquote></div>
<!-- variables.cc -->
<p><a name="doc_002dmunlock"></a>
<div class="defun">
— Built-in Function: <b>munlock</b> (<var>fcn</var>)<var><a name="index-munlock-640"></a></var><br>
<blockquote><p>Unlock the named function. If no function is named
then unlock the current function.
<!-- Texinfo @sp should work but in practice produces ugly results for HTML. -->
<!-- A simple blank line produces the correct behavior. -->
<!-- @sp 1 -->
<p class="noindent"><strong>See also:</strong> <a href="doc_002dmlock.html#doc_002dmlock">mlock</a>, <a href="doc_002dmislocked.html#doc_002dmislocked">mislocked</a>, <a href="doc_002dpersistent.html#doc_002dpersistent">persistent</a>.
</p></blockquote></div>
<!-- variables.cc -->
<p><a name="doc_002dmislocked"></a>
<div class="defun">
— Built-in Function: <b>mislocked</b> (<var>fcn</var>)<var><a name="index-mislocked-641"></a></var><br>
<blockquote><p>Return true if the named function is locked. If no function is named
then return true if the current function is locked.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dmlock.html#doc_002dmlock">mlock</a>, <a href="doc_002dmunlock.html#doc_002dmunlock">munlock</a>, <a href="doc_002dpersistent.html#doc_002dpersistent">persistent</a>.
</p></blockquote></div>
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