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The sigwaitinfo() function 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 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 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() function behaves the same as the sigwait(2) function if the info argument is NULL. If the info argument is non-NULL, the sigwaitinfo() function behaves the same as sigwait(2), except that 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 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 will 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 will be reset. If the value of the si_code member is SI_NOINFO, only the si_signo member of siginfo_t is meaningful, and the value of all other members is unspecified.
The sigtimedwait() function behaves the same as 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.
If, while sigwaitinfo() or sigtimedwait() is waiting, a signal occurs which is eligible for delivery (that is, not blocked by the process signal mask), that signal is handled asynchronously and the wait is interrupted.
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