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+<!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">
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+<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR">
+<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 &lt;pthread.h&gt;</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
+&lt;Xavier.Leroy@inria.fr&gt;
+</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 *) &amp;mut);
+pthread_mutex_lock(&amp;mut);
+/* do some work */
+pthread_mutex_unlock(&amp;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, &amp;oldtype);
+pthread_cleanup_push(pthread_mutex_unlock, (void *) &amp;mut);
+pthread_mutex_lock(&amp;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> \ No newline at end of file