NAME

     sigtimedwait, sigwaitinfo — wait for queued signals (REALTIME)

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <signal.h>

     int
     sigtimedwait(const sigset_t *restrict set, siginfo_t *restrict info,
         const struct timespec *restrict timeout);

     int
     sigwaitinfo(const sigset_t * restrict set, siginfo_t * restrict info);

DESCRIPTION

     The sigtimedwait() system call is equivalent to sigwaitinfo() except that if none of the
     signals specified by set are pending, sigtimedwait() waits for the time interval specified
     in the timespec structure referenced 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() returns immediately with an error.  If timeout is the NULL pointer, the
     behavior is unspecified.  CLOCK_MONOTONIC clock is used to measure the time interval
     specified by the timeout argument.

     The sigwaitinfo() system call selects the pending signal from the set specified by set.
     Should any of multiple pending signals in the range SIGRTMIN to SIGRTMAX be selected, it
     shall be the lowest numbered one.  The selection order between realtime and non-realtime
     signals, or between multiple pending non-realtime signals, is unspecified.  If no signal in
     set is pending at the time of the call, the calling thread is suspended until one or more
     signals in set become pending or until it is interrupted by an unblocked, caught signal.

     The sigwaitinfo() system call is equivalent to the sigwait() system call if the info
     argument is NULL.  If the info argument is non-NULL, the sigwaitinfo() function is
     equivalent to sigwait(), except that the selected signal number shall be stored in the
     si_signo member, and the cause of the signal shall be stored in the si_code member.  Besides
     this, the sigwaitinfo() and sigtimedwait() system calls may return EINTR if interrupted by
     signal, which is not allowed for the sigwait() function.

     If any value is queued to the selected signal, the first such queued value is dequeued and,
     if the info argument is non-NULL, the value is stored in the si_value member of info.  The
     system resource used to queue the signal is released and returned to the system for other
     use.  If no value is queued, the content of the si_value member is zero-valued.  If no
     further signals are queued for the selected signal, the pending indication for that signal
     is reset.

RETURN VALUES

     Upon successful completion (that is, one of the signals specified by set is pending or is
     generated) sigwaitinfo() and sigtimedwait() return the selected signal number.  Otherwise,
     the functions return a value of -1 and set the global variable errno to indicate the error.

ERRORS

     The sigtimedwait() system call will fail if:

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

     The sigtimedwait() and sigwaitinfo() system calls fail if:

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

     The sigtimedwait() system call may also fail if:

     [EINVAL]           The timeout argument specified a tv_nsec value less than zero or greater
                        than or equal to 1000 million.  Kernel only checks for this error if no
                        signal is pending in set and it is necessary to wait.

SEE ALSO

     sigaction(2), sigpending(2), sigqueue(2), sigsuspend(2), sigwait(2), pause(3),
     pthread_sigmask(3), siginfo(3)

STANDARDS

     The sigtimedwait() and sigwaitinfo() system calls conform to ISO/IEC 9945-1:1996
     (“POSIX.1”).