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     sigwait — select a set of signals


     Standard C Library (libc, -lc)


     #include <signal.h>

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


     The sigwait() system call selects a set of signals, specified by set.  If
     none of the selected signals are pending, sigwait() waits until one or
     more of the selected signals has been generated.  Then sigwait()
     atomically clears one of the selected signals from the set of pending
     signals for the process and sets the location pointed to by sig to the
     signal number that was cleared.

     The signals specified by set should be blocked at the time of the call to

     If more than one thread is using sigwait() to wait for the same signal,
     no more than one of these threads will return from sigwait() with the
     signal number.  If more than a single thread is blocked in sigwait() for
     a signal when that signal is generated for the process, it is unspecified
     which of the waiting threads returns from sigwait().  If the signal is
     generated for a specific thread, as by pthread_kill(), only that thread
     will return.

     Should any of the multiple pending signals in the range SIGRTMIN to
     SIGRTMAX be selected, it will be the lowest numbered one.  The selection
     order between realtime and non-realtime signals, or between multiple
     pending non-realtime signals, is unspecified.


     If successful, sigwait() returns 0 and sets the location pointed to by
     sig to the cleared signal number.  Otherwise, an error number is


     The sigwait() system call will fail if:

     [EINVAL]           The set argument specifies one or more invalid signal

     [EFAULT]           Any arguments point outside the allocated address
                        space or there is a memory protection fault.


     sigaction(2), sigpending(2), sigqueue(2), sigsuspend(2), sigtimedwait(2),
     sigwaitinfo(2), pause(3), pthread_sigmask(3)


     The sigwait() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).