140 lines
6.9 KiB
HTML
140 lines
6.9 KiB
HTML
<!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>
|