- wait for queued signals
cc [ flag... ] file... -lrt [ library... ] #include <signal.h> int sigwaitinfo(const sigset_t *restrict set, siginfo_t *restrict info);
int sigtimedwait(const sigset_t *restrict set, siginfo_t *restrict info, const struct timespec *restrict timeout);
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.
Upon successful completion (that is, one of the signals specified by set is pending or is generated) sigwaitinfo() and sigtimedwait() will return the selected signal number. Otherwise, the function returns -1 and sets errno to indicate the error.
The sigwaitinfo() and sigtimedwait() functions will fail if:
The wait was interrupted by an unblocked, caught signal.
The sigwaitinfo() and sigtimedwait() functions are not supported.
The sigtimedwait() function will fail if:
No signal specified by set was generated within the specified timeout period.
The sigwaitinfo() and sigtimedwait() functions may fail if:
The set, info, or timeout argument points to an invalid address.
The sigtimedwait() function may fail if:
The timeout argument specified a tv_nsec value less than zero or greater than or equal to 1000 million. The system only checks for this error if no signal is pending in set and it is necessary to wait.
See attributes(5) for descriptions of the following attributes: