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6.9 KiB
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141 lines
6.9 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8">
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<TITLE>PTHREAD_CLEANUP(3) manual page</TITLE>
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<META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)">
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<META NAME="CREATED" CONTENT="20050504;20152200">
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<META NAME="CHANGED" CONTENT="20050505;18252600">
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<!-- manual page source format generated by PolyglotMan v3.2, -->
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<!-- available at http://polyglotman.sourceforge.net/ -->
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</HEAD>
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<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR">
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<H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4>
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<P><A HREF="index.html">Reference Index</A></P>
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<P><A HREF="#toc">Table of Contents</A></P>
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<H2><A HREF="#toc0" NAME="sect0">Name</A></H2>
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<P>pthread_cleanup_push, pthread_cleanup_pop - install and remove
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cleanup handlers
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</P>
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<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
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<P><B>#include <pthread.h></B>
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</P>
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<P><B>void pthread_cleanup_push(void (*</B><I>routine</I><B>) (void
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*), void *</B><I>arg</I><B>);</B>
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</P>
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<P><B>void pthread_cleanup_pop(int </B><I>execute</I><B>);</B>
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</P>
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<H2><A HREF="#toc2" NAME="sect2">Description</A></H2>
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<P>Cleanup handlers are functions that get called when a thread
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terminates, either by calling <A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A>
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or because of cancellation. Cleanup handlers are installed and
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removed following a stack-like discipline.
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</P>
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<P>The purpose of cleanup handlers is to free the resources that a
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thread may hold at the time it terminates. In particular, if a thread
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exits or is cancelled while it owns a locked mutex, the mutex will
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remain locked forever and prevent other threads from executing
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normally. The best way to avoid this is, just before locking the
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mutex, to install a cleanup handler whose effect is to unlock the
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mutex. Cleanup handlers can be used similarly to free blocks
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allocated with <A HREF="malloc.html"><B>malloc</B>(3)</A> or close
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file descriptors on thread termination.
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</P>
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<P><B>pthread_cleanup_push</B> installs the <I>routine</I> function
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with argument <I>arg</I> as a cleanup handler. From this point on to
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the matching <B>pthread_cleanup_pop</B>, the function <I>routine</I>
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will be called with arguments <I>arg</I> when the thread terminates,
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either through <A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A>
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or by cancellation. If several cleanup handlers are active at that
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point, they are called in LIFO order: the most recently installed
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handler is called first.
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</P>
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<P><B>pthread_cleanup_pop</B> removes the most recently installed
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cleanup handler. If the <I>execute</I> argument is not 0, it also
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executes the handler, by calling the <I>routine</I> function with
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arguments <I>arg</I>. If the <I>execute</I> argument is 0, the
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handler is only removed but not executed.
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</P>
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<P>Matching pairs of <B>pthread_cleanup_push</B> and
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<B>pthread_cleanup_pop</B> must occur in the same function, at the
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same level of block nesting. Actually, <B>pthread_cleanup_push</B>
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and <B>pthread_cleanup_pop</B> are macros, and the expansion of
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<B>pthread_cleanup_push</B> introduces an open brace <B>{</B> with
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the matching closing brace <B>}</B> being introduced by the expansion
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of the matching <B>pthread_cleanup_pop</B>.
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</P>
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<H2 STYLE="margin-top: 0cm"><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">None.
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</BLOCKQUOTE>
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<H2 STYLE="margin-top: 0cm"><A HREF="#toc4" NAME="sect4">Errors</A></H2>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">None.
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</BLOCKQUOTE>
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<H2 STYLE="margin-top: 0cm"><A HREF="#toc5" NAME="sect5">Author</A></H2>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">Xavier Leroy
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<Xavier.Leroy@inria.fr>
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</BLOCKQUOTE>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">Modified by
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Ross Johnson for use with Pthreads-w32.</BLOCKQUOTE>
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<H2 STYLE="margin-top: 0cm"><A HREF="#toc6" NAME="sect6">See Also</A></H2>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"><A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A>
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, <A HREF="pthread_cancel.html"><B>pthread_cancel</B>(3)</A> ,
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<A HREF="pthread_cancel.html"><B>pthread_setcanceltype</B>(3)</A> .
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</BLOCKQUOTE>
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<H2 STYLE="margin-top: 0cm"><A HREF="#toc7" NAME="sect7">Example</A></H2>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">Here is how
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to lock a mutex <I>mut</I> in such a way that it will be unlocked if
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the thread is canceled while <I>mut</I> is locked:
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</BLOCKQUOTE>
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<PRE>pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
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pthread_mutex_lock(&mut);
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/* do some work */
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pthread_mutex_unlock(&mut);
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pthread_cleanup_pop(0);</PRE><BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">
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Equivalently, the last two lines can be replaced by
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</BLOCKQUOTE>
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<PRE STYLE="margin-bottom: 0.5cm">pthread_cleanup_pop(1);</PRE><BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">
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Notice that the code above is safe only in deferred cancellation mode
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(see <A HREF="pthread_cancel.html"><B>pthread_setcanceltype</B>(3)</A>
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). In asynchronous cancellation mode, a cancellation can occur
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between <B>pthread_cleanup_push</B> and <B>pthread_mutex_lock</B>, or
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between <B>pthread_mutex_unlock</B> and <B>pthread_cleanup_pop</B>,
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resulting in both cases in the thread trying to unlock a mutex not
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locked by the current thread. This is the main reason why
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asynchronous cancellation is difficult to use.
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</BLOCKQUOTE>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">If the code
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above must also work in asynchronous cancellation mode, then it must
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switch to deferred mode for locking and unlocking the mutex:
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</BLOCKQUOTE>
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<PRE>pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
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pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
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pthread_mutex_lock(&mut);
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/* do some work */
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pthread_cleanup_pop(1);
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pthread_setcanceltype(oldtype, NULL);</PRE>
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<HR>
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<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"><A NAME="toc"></A>
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<B>Table of Contents</B></BLOCKQUOTE>
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<UL>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A>
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</BLOCKQUOTE>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A>
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</BLOCKQUOTE>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A>
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</BLOCKQUOTE>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Return
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Value</A>
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</BLOCKQUOTE>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A>
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</BLOCKQUOTE>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Author</A>
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</BLOCKQUOTE>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">See
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Also</A>
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</BLOCKQUOTE>
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<LI><BLOCKQUOTE STYLE="margin-right: 0cm"><A HREF="#sect7" NAME="toc7">Example</A>
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</BLOCKQUOTE>
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</UL>
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</BODY>
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</HTML>
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