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RedHat 9 (Linux i386) - man page for pthread_sigmask (redhat section 3)

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       pthread_sigmask, pthread_kill, sigwait - handling of signals in threads

       #include <pthread.h>
       #include <signal.h>

       int pthread_sigmask(int how, const sigset_t *newmask, sigset_t *oldmask);

       int pthread_kill(pthread_t thread, int signo);

       int sigwait(const sigset_t *set, int *sig);

       pthread_sigmask changes the signal mask for the calling thread as described by the how and
       newmask arguments. If oldmask is not NULL, the previous signal mask is stored in the loca-
       tion pointed to by oldmask.

       The meaning of the how and newmask arguments is the same as for sigprocmask(2).	If how is
       SIG_SETMASK, the signal mask is set to newmask.	If how is SIG_BLOCK, the  signals  speci-
       fied  to newmask are added to the current signal mask.  If how is SIG_UNBLOCK, the signals
       specified to newmask are removed from the current signal mask.

       Recall that signal masks are set on a per-thread basis, but signal actions and signal han-
       dlers, as set with sigaction(2), are shared between all threads.

       pthread_kill  send  signal number signo to the thread thread.  The signal is delivered and
       handled as described in kill(2).

       sigwait suspends the calling thread until one of the signals in set is  delivered  to  the
       calling	thread.  It then stores the number of the signal received in the location pointed
       to by sig and returns. The signals in set must be blocked and not ignored on  entrance  to
       sigwait.  If the delivered signal has a signal handler function attached, that function is
       not called.

       sigwait is a cancellation point.

       On success, 0 is returned. On failure, a non-zero error code is returned.

       The pthread_sigmask function returns the following error codes on error:

	      EINVAL how is not one of SIG_SETMASK, SIG_BLOCK, or SIG_UNBLOCK

	      EFAULT newmask or oldmask point to invalid addresses

       The pthread_kill function returns the following error codes on error:

	      EINVAL signo is not a valid signal number

	      ESRCH  the thread thread does not exist (e.g. it has already terminated)

       The sigwait function never returns an error.

       Xavier Leroy <Xavier.Leroy@inria.fr>

       sigprocmask(2), kill(2), sigaction(2), sigsuspend(2).

       For sigwait to work reliably, the signals being waited for must be blocked in all threads,
       not only in the calling thread, since otherwise the POSIX semantics for signal delivery do
       not guarantee that it's the thread doing the sigwait that will receive  the  signal.   The
       best  way to achieve this is block those signals before any threads are created, and never
       unblock them in the program other than by calling sigwait.

       Signal handling in LinuxThreads departs significantly from the POSIX  standard.	According
       to  the	standard,  ``asynchronous'' (external) signals are addressed to the whole process
       (the collection of all threads), which then delivers them to one  particular  thread.  The
       thread  that  actually receives the signal is any thread that does not currently block the

       In LinuxThreads, each thread is actually a kernel process with its own  PID,  so  external
       signals are always directed to one particular thread.  If, for instance, another thread is
       blocked in sigwait on that signal, it will not be restarted.

       The LinuxThreads implementation of sigwait installs dummy signal handlers for the  signals
       in set for the duration of the wait. Since signal handlers are shared between all threads,
       other threads must not attach their own signal handlers to these signals, or alternatively
       they  should  all  block  these signals (which is recommended anyway -- see the Notes sec-

					   LinuxThreads 			PTHREAD_SIGNAL(3)
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