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| author | rpj <rpj> | 2005-05-06 07:27:10 +0000 |
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| committer | rpj <rpj> | 2005-05-06 07:27:10 +0000 |
| commit | 7523c7c4d75652f67cd31cb123e1268790394c8b (patch) | |
| tree | 0920ebf089ccb971e0878542f85486171a541a8a /manual/pthread_cancel.html | |
| parent | cf42850c77554311e62d3780f6a36cbc38e5e002 (diff) | |
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diff --git a/manual/pthread_cancel.html b/manual/pthread_cancel.html new file mode 100644 index 0000000..d9acd77 --- /dev/null +++ b/manual/pthread_cancel.html @@ -0,0 +1,205 @@ +<!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_CANCEL(3) manual page</TITLE> + <META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)"> + <META NAME="CREATED" CONTENT="20050504;12090500"> + <META NAME="CHANGED" CONTENT="20050505;18220000"> + <!-- 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_cancel, pthread_setcancelstate, pthread_setcanceltype, +pthread_testcancel - thread cancellation +</P> +<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2> +<P><B>#include <pthread.h></B> +</P> +<P><B>int pthread_cancel(pthread_t </B><I>thread</I><B>);</B> +</P> +<P><B>int pthread_setcancelstate(int </B><I>state</I><B>, int +*</B><I>oldstate</I><B>);</B> +</P> +<P><B>int pthread_setcanceltype(int </B><I>type</I><B>, int +*</B><I>oldtype</I><B>);</B> +</P> +<P><B>void pthread_testcancel(void);</B> +</P> +<H2><A HREF="#toc2" NAME="sect2">Description</A></H2> +<P>Cancellation is the mechanism by which a thread can terminate the +execution of another thread. More precisely, a thread can send a +cancellation request to another thread. Depending on its settings, +the target thread can then either ignore the request, honor it +immediately, or defer it until it reaches a cancellation point. +</P> +<P>When a thread eventually honors a cancellation request, it +performs as if <B>pthread_exit(PTHREAD_CANCELED)</B> has been called +at that point: all cleanup handlers are executed in reverse order, +destructor functions for thread-specific data are called, and finally +the thread stops executing with the return value <B>PTHREAD_CANCELED</B>. +See <A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A> for more +information. +</P> +<P><B>pthread_cancel</B> sends a cancellation request to the thread +denoted by the <I>thread</I> argument. +</P> +<P><B>pthread_setcancelstate</B> changes the cancellation state for +the calling thread -- that is, whether cancellation requests are +ignored or not. The <I>state</I> argument is the new cancellation +state: either <B>PTHREAD_CANCEL_ENABLE</B> to enable cancellation, or +<B>PTHREAD_CANCEL_DISABLE</B> to disable cancellation (cancellation +requests are ignored). If <I>oldstate</I> is not <B>NULL</B>, the +previous cancellation state is stored in the location pointed to by +<I>oldstate</I>, and can thus be restored later by another call to +<B>pthread_setcancelstate</B>. +</P> +<P><B>pthread_setcanceltype</B> changes the type of responses to +cancellation requests for the calling thread: asynchronous +(immediate) or deferred. The <I>type</I> argument is the new +cancellation type: either <B>PTHREAD_CANCEL_ASYNCHRONOUS</B> to +cancel the calling thread as soon as the cancellation request is +received, or <B>PTHREAD_CANCEL_DEFERRED</B> to keep the cancellation +request pending until the next cancellation point. If <I>oldtype</I> +is not <B>NULL</B>, the previous cancellation state is stored in the +location pointed to by <I>oldtype</I>, and can thus be restored later +by another call to <B>pthread_setcanceltype</B>. +</P> +<P><B>Pthreads-w32</B> provides two levels of support for +<B>PTHREAD_CANCEL_ASYNCHRONOUS</B>: full and partial. Full support +requires an additional DLL and driver be installed on the Windows +system (see the See Also section below) that allows blocked threads +to be cancelled immediately. Partial support means that the target +thread will not cancel until it resumes execution naturally. Partial +support is provided if either the DLL or the driver are not +automatically detected by the pthreads-w32 library at run-time.</P> +<P>Threads are always created by <A HREF="pthread_create.html"><B>pthread_create</B>(3)</A> +with cancellation enabled and deferred. That is, the initial +cancellation state is <B>PTHREAD_CANCEL_ENABLE</B> and the initial +type is <B>PTHREAD_CANCEL_DEFERRED</B>. +</P> +<P>Cancellation points are those points in the program execution +where a test for pending cancellation requests is performed and +cancellation is executed if positive. The following POSIX threads +functions are cancellation points: +</P> +<P><A HREF="pthread_join.html"><B>pthread_join</B>(3)</A> +<BR><A HREF="pthread_cond_init.html"><B>pthread_cond_wait</B>(3)</A> +<BR><A HREF="pthread_cond_init.html"><B>pthread_cond_timedwait</B>(3)</A> +<BR><A HREF=""><B>pthread_testcancel</B>(3)</A> <BR><A HREF="sem_init.html"><B>sem_wait</B>(3)</A> +<BR><A HREF="sem_init.html"><B>sem_timedwait</B>(3)</A> <BR><A HREF="pthread_kill.html"><B>sigwait</B>(3)</A></P> +<P><B>Pthreads-w32</B> provides two functions to enable additional +cancellation points to be created in user functions that block on +Win32 HANDLEs:</P> +<P><A HREF="pthreadCancelableWait.html">pthreadCancelableWait()</A> +<BR><A HREF="pthreadCancelableTimedWait.html">pthreadCancelableTimedWait()</A></P> +<P>All other POSIX threads functions are guaranteed not to be +cancellation points. That is, they never perform cancellation in +deferred cancellation mode. +</P> +<P><B>pthread_testcancel</B> does nothing except testing for pending +cancellation and executing it. Its purpose is to introduce explicit +checks for cancellation in long sequences of code that do not call +cancellation point functions otherwise. +</P> +<H2><A HREF="#toc3" NAME="sect3">Return Value</A></H2> +<P><B>pthread_cancel</B>, <B>pthread_setcancelstate</B> and +<B>pthread_setcanceltype</B> return 0 on success and a non-zero error +code on error. +</P> +<H2><A HREF="#toc4" NAME="sect4">Errors</A></H2> +<P><B>pthread_cancel</B> returns the following error code on error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>ESRCH</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + no thread could be found corresponding to that specified by the + <I>thread</I> ID. + </DD></DL> +</DL> +<P> +<B>pthread_setcancelstate</B> returns the following error code on +error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the <I>state</I> argument is not + </DD></DL> +</DL> +<BLOCKQUOTE> +<B>PTHREAD_CANCEL_ENABLE</B> nor <B>PTHREAD_CANCEL_DISABLE</B> +</BLOCKQUOTE> +<P><B>pthread_setcanceltype</B> returns the following error code on +error: +</P> +<DL> + <DL> + <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B> + </DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm"> + the <I>type</I> argument is not + </DD></DL> +</DL> +<BLOCKQUOTE> +<B>PTHREAD_CANCEL_DEFERRED</B> nor <B>PTHREAD_CANCEL_ASYNCHRONOUS</B> +</BLOCKQUOTE> +<H2><A HREF="#toc5" NAME="sect5">Author</A></H2> +<P>Xavier Leroy <Xavier.Leroy@inria.fr> +</P> +<P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P> +<H2><A HREF="#toc6" NAME="sect6">See Also</A></H2> +<P><A HREF="pthread_exit.html"><B>pthread_exit</B>(3)</A> , +<A HREF="pthread_cleanup_push.html"><B>pthread_cleanup_push</B>(3)</A> +, <A HREF="pthread_cleanup_pop.html"><B>pthread_cleanup_pop</B>(3)</A> +, Pthreads-w32 package README file 'Prerequisites' section. +</P> +<H2><A HREF="#toc7" NAME="sect7">Bugs</A></H2> +<P>POSIX specifies that a number of system calls (basically, all +system calls that may block, such as <A HREF="read.html"><B>read</B>(2)</A> +, <A HREF="write.html"><B>write</B>(2)</A> , <A HREF="wait.html"><B>wait</B>(2)</A> +, etc.) and library functions that may call these system calls (e.g. +<A HREF="fprintf.html"><B>fprintf</B>(3)</A> ) are cancellation +points. <B>Pthreads-win32</B> is not integrated enough with the C +library to implement this, and thus none of the C library functions +is a cancellation point. +</P> +<P>A workaround for these calls is to temporarily switch to +asynchronous cancellation (assuming full asynchronous cancellation +support is installed). So, checking for cancellation during a <B>read</B> +system call, for instance, can be achieved as follows: +</P> +<BLOCKQUOTE><BR><BR> +</BLOCKQUOTE> +<PRE STYLE="margin-left: 1cm; margin-right: 1cm">pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &oldCancelType); +read(fd, buffer, length); +pthread_setcanceltype(oldCancelType, NULL);</PRE> +<HR> +<BLOCKQUOTE><A NAME="toc"></A><B>Table of Contents</B></BLOCKQUOTE> +<UL> + <LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Return + Value</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Author</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">See + Also</A> + </BLOCKQUOTE> + <LI><BLOCKQUOTE><A HREF="#sect7" NAME="toc7">Bugs</A> + </BLOCKQUOTE> +</UL> +</BODY> +</HTML> |