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| author | rpj <rpj> | 2005-05-06 07:27:10 +0000 |
|---|---|---|
| committer | rpj <rpj> | 2005-05-06 07:27:10 +0000 |
| commit | 7523c7c4d75652f67cd31cb123e1268790394c8b (patch) | |
| tree | 0920ebf089ccb971e0878542f85486171a541a8a /manual/pthread_cleanup_push.html | |
| parent | cf42850c77554311e62d3780f6a36cbc38e5e002 (diff) | |
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| -rw-r--r-- | manual/pthread_cleanup_push.html | 140 |
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diff --git a/manual/pthread_cleanup_push.html b/manual/pthread_cleanup_push.html new file mode 100644 index 0000000..0fc071e --- /dev/null +++ b/manual/pthread_cleanup_push.html @@ -0,0 +1,140 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<HTML> +<HEAD> + <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8"> + <TITLE>PTHREAD_CLEANUP(3) manual page</TITLE> + <META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)"> + <META NAME="CREATED" CONTENT="20050504;20152200"> + <META NAME="CHANGED" CONTENT="20050505;18252600"> + <!-- manual page source format generated by PolyglotMan v3.2, --> + <!-- available at http://polyglotman.sourceforge.net/ --> +</HEAD> +<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR"> +<H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4> +<P><A HREF="index.html">Reference Index</A></P> +<P><A HREF="#toc">Table of Contents</A></P> +<H2><A HREF="#toc0" NAME="sect0">Name</A></H2> +<P>pthread_cleanup_push, pthread_cleanup_pop - install and remove +cleanup handlers +</P> +<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2> +<P><B>#include <pthread.h></B> +</P> +<P><B>void pthread_cleanup_push(void (*</B><I>routine</I><B>) (void +*), void *</B><I>arg</I><B>);</B> +</P> +<P><B>void pthread_cleanup_pop(int </B><I>execute</I><B>);</B> +</P> +<H2><A HREF="#toc2" NAME="sect2">Description</A></H2> +<P>Cleanup handlers are functions that get called when a thread +terminates, either by calling <A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A> +or because of cancellation. Cleanup handlers are installed and +removed following a stack-like discipline. +</P> +<P>The purpose of cleanup handlers is to free the resources that a +thread may hold at the time it terminates. In particular, if a thread +exits or is cancelled while it owns a locked mutex, the mutex will +remain locked forever and prevent other threads from executing +normally. The best way to avoid this is, just before locking the +mutex, to install a cleanup handler whose effect is to unlock the +mutex. Cleanup handlers can be used similarly to free blocks +allocated with <A HREF="malloc.html"><B>malloc</B>(3)</A> or close +file descriptors on thread termination. +</P> +<P><B>pthread_cleanup_push</B> installs the <I>routine</I> function +with argument <I>arg</I> as a cleanup handler. From this point on to +the matching <B>pthread_cleanup_pop</B>, the function <I>routine</I> +will be called with arguments <I>arg</I> when the thread terminates, +either through <A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A> +or by cancellation. If several cleanup handlers are active at that +point, they are called in LIFO order: the most recently installed +handler is called first. +</P> +<P><B>pthread_cleanup_pop</B> removes the most recently installed +cleanup handler. If the <I>execute</I> argument is not 0, it also +executes the handler, by calling the <I>routine</I> function with +arguments <I>arg</I>. If the <I>execute</I> argument is 0, the +handler is only removed but not executed. +</P> +<P>Matching pairs of <B>pthread_cleanup_push</B> and +<B>pthread_cleanup_pop</B> must occur in the same function, at the +same level of block nesting. Actually, <B>pthread_cleanup_push</B> +and <B>pthread_cleanup_pop</B> are macros, and the expansion of +<B>pthread_cleanup_push</B> introduces an open brace <B>{</B> with +the matching closing brace <B>}</B> being introduced by the expansion +of the matching <B>pthread_cleanup_pop</B>. +</P> +<H2 STYLE="margin-top: 0cm"><A HREF="#toc3" NAME="sect3">Return Value</A></H2> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">None. +</BLOCKQUOTE> +<H2 STYLE="margin-top: 0cm"><A HREF="#toc4" NAME="sect4">Errors</A></H2> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">None. +</BLOCKQUOTE> +<H2 STYLE="margin-top: 0cm"><A HREF="#toc5" NAME="sect5">Author</A></H2> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">Xavier Leroy +<Xavier.Leroy@inria.fr> +</BLOCKQUOTE> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">Modified by +Ross Johnson for use with Pthreads-w32.</BLOCKQUOTE> +<H2 STYLE="margin-top: 0cm"><A HREF="#toc6" NAME="sect6">See Also</A></H2> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"><A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A> +, <A HREF="pthread_cancel.html"><B>pthread_cancel</B>(3)</A> , +<A HREF="pthread_cancel.html"><B>pthread_setcanceltype</B>(3)</A> . +</BLOCKQUOTE> +<H2 STYLE="margin-top: 0cm"><A HREF="#toc7" NAME="sect7">Example</A></H2> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">Here is how +to lock a mutex <I>mut</I> in such a way that it will be unlocked if +the thread is canceled while <I>mut</I> is locked: +</BLOCKQUOTE> +<PRE>pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut); +pthread_mutex_lock(&mut); +/* do some work */ +pthread_mutex_unlock(&mut); +pthread_cleanup_pop(0);</PRE><BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"> +Equivalently, the last two lines can be replaced by +</BLOCKQUOTE> +<PRE STYLE="margin-bottom: 0.5cm">pthread_cleanup_pop(1);</PRE><BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"> +Notice that the code above is safe only in deferred cancellation mode +(see <A HREF="pthread_cancel.html"><B>pthread_setcanceltype</B>(3)</A> +). In asynchronous cancellation mode, a cancellation can occur +between <B>pthread_cleanup_push</B> and <B>pthread_mutex_lock</B>, or +between <B>pthread_mutex_unlock</B> and <B>pthread_cleanup_pop</B>, +resulting in both cases in the thread trying to unlock a mutex not +locked by the current thread. This is the main reason why +asynchronous cancellation is difficult to use. +</BLOCKQUOTE> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm">If the code +above must also work in asynchronous cancellation mode, then it must +switch to deferred mode for locking and unlocking the mutex: +</BLOCKQUOTE> +<PRE>pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype); +pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut); +pthread_mutex_lock(&mut); +/* do some work */ +pthread_cleanup_pop(1); +pthread_setcanceltype(oldtype, NULL);</PRE> +<HR> +<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"><A NAME="toc"></A> +<B>Table of Contents</B></BLOCKQUOTE> +<UL> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Return + Value</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Author</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm; margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">See + Also</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-right: 0cm"><A HREF="#sect7" NAME="toc7">Example</A> + </BLOCKQUOTE> +</UL> +</BODY> +</HTML> |