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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 or for the current thread) 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 sigwait().

     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.


     The sigwait() function is implemented as a wrapper around the __sys_sigwait() system call,
     which retries the call on EINTR error.


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


     The sigwait() system call will fail if:

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


     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”).