SIGWAIT(3)                                                          SIGWAIT(3)


NAME
     sigwait, sigwaitinfo, sigtimedwait - wait for queued signals (POSIX)

C SYNOPSIS
     #include <signal.h>
     #include <sys/timers.h>

     int sigwait(const sigset_t *set, int *sig);
     int sigwaitinfo(const sigset_t *set, siginfo_t *value);
     int sigtimedwait(const sigset_t *set, siginfo_t *value, timespec_t *timeout);

DESCRIPTION
     The sigwait() function selects a pending signal from set and returns it
     in the storage pointed to by sig. If multiple signals from set are
     pending, then the one with the lowest numerical value is selected.  If no
     signals in set are pending then the call will block until one becomes
     pending, The signals defined by set must be blocked at the time of the
     call to sigwait() in order to avoid conflicts with installed signal
     handlers.  If the signals in set are not blocked then the system will
     either deliver the signal asynchronously, or sigwait() will return with
     the signal. Users are advised to always block signals in set to get
     predictable results.

     The sigwaitinfo() call behaves the same as the sigwait() call if the
     value argument is NULL. If the value argument is non-NULL, the
     sigwaitinfo() function behaves the same as sigwait() except the selected
     signal number is stored in the si_signo member, and the cause of the
     signal is stored in the si_code member. If any value was queued to the
     selected signal, the first such queued value is dequeued and the value is
     stored in the si_value member of value. The system resource used to queue
     the signal shall be released and made available to queue other signals.
     If no value is queued, the content of the si_value member is undefined.
     If no further signals are queued for the selected signal, the pending
     indication for that signal shall be reset.

     The function sigtimedwait() behaves the same as sigwaitinfo() except that
     if none of the signals specified by set are pending, sigtimedwait() shall
     wait for the time interval specified in the timespec structure pointed to
     by timeout. If the timespec structure pointed to by timeout is zero-
     valued and if none of the signals specified by set are pending, then
     sigtimedwait() shall return immediately with an error. If timeout is the
     NULL pointer, the behavior is the same as sigwaitinfo()

     If any realtime signals (those in the range SIGRTMIN to SIGRTMAX) are
     pending, the lowest numbered signal shall be returned.  The order in
     which realtime and nonrealtime signals are returned is nondeterministic.
     The order in which multiple nonrealtime signals are returned is also
     nondeterministic.


SEE ALSO
     kill(2), sigaction(2), sigqueue(3), signal(5), pthread_sigmask(3P).

DIAGNOSTICS
     Upon successful completion, sigwait() returns a 0.  Otherwise, it returns
     an error number to indicate the error.

     Upon successful completion, sigwaitinfo() and sigtimedwait() return the
     selected signal number.  Otherwise, they return a -1 and set errno to
     indicate the error number.

     If any of the conditions below occur, the error number will take on the
     corresponding value:

     [EINTR]        The wait was interrupted by an unblocked, caught signal.

     If any of the following conditions occur, the sigwait() function shall
     return the corresponding value:

     [EINVAL]       The set argument contains an invalid or unsupported signal
                    number.

     If any of the following conditions occur, the sigtimedwait() function
     shall return -1 and set errno to the corresponding value:

     [EAGAIN]       No signal specified by set was delivered within the
                    specified timeout period.

     [EINVAL]       The timeout argument specified a tv_nsec value less than
                    zero or greater than or equal to 1 billion.

WARNING
     The POSIX and System V signal facilities have different semantics.  Using
     both facilities in the same program is strongly discouraged and will
     result in unpredictable behavior.


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