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<h3 class="section">8.8 Synchronization</h3>
<p>GNU Objective-C provides support for synchronized blocks:
<pre class="smallexample"> @synchronized (ObjCClass *guard) {
...
}
</pre>
<p>Upon entering the <code>@synchronized</code> block, a thread of execution
shall first check whether a lock has been placed on the corresponding
<code>guard</code> object by another thread. If it has, the current thread
shall wait until the other thread relinquishes its lock. Once
<code>guard</code> becomes available, the current thread will place its own
lock on it, execute the code contained in the <code>@synchronized</code>
block, and finally relinquish the lock (thereby making <code>guard</code>
available to other threads).
<p>Unlike Java, Objective-C does not allow for entire methods to be
marked <code>@synchronized</code>. Note that throwing exceptions out of
<code>@synchronized</code> blocks is allowed, and will cause the guarding
object to be unlocked properly.
<p>Because of the interactions between synchronization and exception
handling, you can only use <code>@synchronized</code> when compiling with
exceptions enabled, that is with the command line option
<samp><span class="option">-fobjc-exceptions</span></samp>.
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