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152 lines
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<TITLE>PTHREAD_SIGNAL(3) manual page</TITLE>
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<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR">
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<H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4>
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<P><A HREF="index.html">Reference Index</A></P>
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<P><A HREF="#toc">Table of Contents</A></P>
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<H2><A HREF="#toc0" NAME="sect0">Name</A></H2>
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<P>pthread_sigmask, pthread_kill, sigwait - handling of signals in
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threads
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</P>
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<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
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<P><B>#include <pthread.h></B> <BR><B>#include <signal.h></B>
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</P>
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<P><B>int pthread_sigmask(int </B><I>how</I><B>, const sigset_t
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*</B><I>newmask</I><B>, sigset_t *</B><I>oldmask</I><B>);</B>
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</P>
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<P><B>int pthread_kill(pthread_t </B><I>thread</I><B>, int </B><I>signo</I><B>);</B>
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</P>
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<P><B>int sigwait(const sigset_t *</B>set, <B>int</B> *sig);</P>
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<H2><A HREF="#toc2" NAME="sect2">Description</A></H2>
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<P><B>pthread_sigmask</B> changes the signal mask for the calling
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thread as described by the <I>how</I> and <I>newmask</I> arguments.
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If <I>oldmask</I> is not <B>NULL</B>, the previous signal mask is
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stored in the location pointed to by <I>oldmask</I>. <B>Pthreads-w32</B>
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implements this function but no other function uses the signal mask
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yet.</P>
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<P>The meaning of the <I>how</I> and <I>newmask</I> arguments is the
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same as for <B><SPAN STYLE="font-style: normal">sigprocmask</SPAN></B>(2).
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If <I>how</I> is <B>SIG_SETMASK</B>, the signal mask is set to
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<I>newmask</I>. If <I>how</I> is <B>SIG_BLOCK</B>, the signals
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specified to <I>newmask</I> are added to the current signal mask. If
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<I>how</I> is <B>SIG_UNBLOCK</B>, the signals specified to <I>newmask</I>
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are removed from the current signal mask.
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</P>
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<P>Recall that signal masks are set on a per-thread basis, but signal
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actions and signal handlers, as set with <B>sigaction</B>(2), are
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shared between all threads.
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</P>
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<P><B>pthread_kill</B> send signal number <I>signo</I> to the thread
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<I>thread</I>. <B>Pthreads-w32</B> only supports signal number 0,
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which does not send any signal but causes <B>pthread_kill</B> to
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return an error if <I>thread</I> is not valid.</P>
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<P><B>sigwait</B> suspends the calling thread until one of the
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signals in <I>set</I> is delivered to the calling thread. It then
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stores the number of the signal received in the location pointed to
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by <I>sig</I> and returns. The signals in <I>set</I> must be blocked
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and not ignored on entrance to <B>sigwait</B>. If the delivered
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signal has a signal handler function attached, that function is <I>not</I>
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called. <B>Pthreads-w32</B> implements this function as a
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cancellation point only - it does not wait for any signals and does
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not change the location pointed to by <I>sig</I>.</P>
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<H2><A HREF="#toc3" NAME="sect3">Cancellation</A></H2>
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<P><B>sigwait</B> is a cancellation point.
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</P>
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<H2><A HREF="#toc4" NAME="sect4">Return Value</A></H2>
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<P>On success, 0 is returned. On failure, a non-zero error code is
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returned.
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</P>
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<H2><A HREF="#toc5" NAME="sect5">Errors</A></H2>
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<P>The <B>pthread_sigmask</B> function returns the following error
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codes on error:
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</P>
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<DL>
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<DL>
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<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B>
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</DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm">
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<I>how</I> is not one of <B>SIG_SETMASK</B>, <B>SIG_BLOCK</B>, or
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<B>SIG_UNBLOCK</B>
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</DD></DL>
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</DL>
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<P>
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The <B>pthread_kill</B> function returns the following error codes on
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error:
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</P>
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<DL>
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<DL>
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<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B>
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</DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm">
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<I>signo</I> is not a valid signal number or is unsupported.</DD><DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm">
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<B>ESRCH</B>
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</DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm">
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the thread <I>thread</I> does not exist (e.g. it has already
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terminated)
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</DD></DL>
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</DL>
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<P>
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The <B>sigwait</B> function never returns an error.
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</P>
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<H2><A HREF="#toc6" NAME="sect6">Author</A></H2>
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<P>Xavier Leroy <Xavier.Leroy@inria.fr>
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</P>
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<P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P>
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<H2><A HREF="#toc7" NAME="sect7">See Also</A></H2>
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<P>
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</P>
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<H2><A HREF="#toc8" NAME="sect8">Notes</A></H2>
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<P>In any implementation, for <B>sigwait</B> to work reliably, the
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signals being waited for must be blocked in all threads, not only in
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the calling thread, since otherwise the POSIX semantics for signal
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delivery do not guarantee that it’s the thread doing the <B>sigwait</B>
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that will receive the signal. The best way to achieve this is to
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block those signals before any threads are created, and never unblock
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them in the program other than by calling <B>sigwait</B>. This works
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because all threads inherit their initial sigmask from their creating
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thread.</P>
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<H2><A HREF="#toc9" NAME="sect9">Bugs</A></H2>
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<P><B>Pthreads-w32</B> does not implement signals yet and so these
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routines have almost no use except to prevent the compiler or linker
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from complaining. <B>pthread_kill</B> is useful in determining if the
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thread is a valid thread, but since many threads implementations
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reuse thread IDs, the valid thread may no longer be the thread you
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think it is, and so this method of determining thread validity is not
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portable, and very risky. <B>Pthreads-w32</B> from version 1.0.0
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onwards implements pseudo-unique thread IDs, so applications that use
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this technique (but really shouldn't) have some protection.</P>
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<HR>
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<P><A NAME="toc"></A><B>Table of Contents</B></P>
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<UL>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Cancellation</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Return
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Value</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Errors</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">Author</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect7" NAME="toc7">See
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Also</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect8" NAME="toc8">Notes</A>
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</P>
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<LI><P><A HREF="#sect9" NAME="toc9">Bugs</A>
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</P>
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</UL>
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