113 lines
4.7 KiB
HTML
113 lines
4.7 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using the GNU Compiler Collection (GCC): Synchronization</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC): Synchronization">
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<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Synchronization">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Objective_002dC.html#Objective_002dC" rel="up" title="Objective-C">
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<link href="Fast-enumeration.html#Fast-enumeration" rel="next" title="Fast enumeration">
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<link href="Exceptions.html#Exceptions" rel="prev" title="Exceptions">
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Synchronization"></a>
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<div class="header">
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<p>
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Next: <a href="Fast-enumeration.html#Fast-enumeration" accesskey="n" rel="next">Fast enumeration</a>, Previous: <a href="Exceptions.html#Exceptions" accesskey="p" rel="prev">Exceptions</a>, Up: <a href="Objective_002dC.html#Objective_002dC" accesskey="u" rel="up">Objective-C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Synchronization-1"></a>
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<h3 class="section">8.8 Synchronization</h3>
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<p>GNU Objective-C provides support for synchronized blocks:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> @synchronized (ObjCClass *guard) {
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…
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}
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</pre></div>
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<p>Upon entering the <code>@synchronized</code> block, a thread of execution
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shall first check whether a lock has been placed on the corresponding
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<code>guard</code> object by another thread. If it has, the current thread
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shall wait until the other thread relinquishes its lock. Once
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<code>guard</code> becomes available, the current thread will place its own
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lock on it, execute the code contained in the <code>@synchronized</code>
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block, and finally relinquish the lock (thereby making <code>guard</code>
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available to other threads).
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</p>
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<p>Unlike Java, Objective-C does not allow for entire methods to be
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marked <code>@synchronized</code>. Note that throwing exceptions out of
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<code>@synchronized</code> blocks is allowed, and will cause the guarding
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object to be unlocked properly.
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</p>
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<p>Because of the interactions between synchronization and exception
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handling, you can only use <code>@synchronized</code> when compiling with
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exceptions enabled, that is with the command line option
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<samp>-fobjc-exceptions</samp>.
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</p>
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</body>
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</html>
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