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| <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> | |
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