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| <a name="Synchronization-1"></a> |
| <h3 class="section">8.8 Synchronization</h3> |
| |
| <p>GNU Objective-C provides support for synchronized blocks: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample"> @synchronized (ObjCClass *guard) { |
| … |
| } |
| </pre></div> |
| |
| <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> |
| <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> |
| <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>-fobjc-exceptions</samp>. |
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