sigtimedwait¶

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);

Status¶

Implemented

Conformance¶

IEEE Std 1003.1-2017

Description¶

The sigtimedwait() function shall be equivalent to 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 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() shall return immediately with an error. If timeout is the NULL pointer, sigtimedwait() waits without a time limit, like sigwaitinfo().

The sigwaitinfo() function selects the pending signal from the set specified by set. The selection order between multiple pending signals is unspecified. If no signal in set is pending at the time of the call, the calling thread shall be suspended until one or more signals in set become pending or until it is interrupted by an unblocked, caught signal.

The sigwaitinfo() function shall be equivalent to the sigwait() function, except that the return value and the error reporting method are different (see Return value), and that if the info argument is non-NULL, 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 (see POSIX deviations). If any value is queued to the selected signal, the first such queued value shall be dequeued and, if the info argument is non-NULL, the value shall be stored in the si_value member of info. 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.

Return value¶

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

Errors¶

The sigtimedwait() function shall fail if:

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

The sigtimedwait() and sigwaitinfo() functions may fail if:

EINTR - The wait was interrupted by an unblocked, caught signal. These functions fail with EINTR in this case.

The sigtimedwait() function may also fail if:

EINVAL - The timeout argument specified a tv_nsec value less than zero or greater than or equal to 1000 million. The error is reported also when a signal in set is pending.

POSIX deviations¶

The cause of the signal is not stored in the si_code member of info: only the si_signo member is set, and the other members of the structure are set to zero. The kernel does not keep the information about the sender of a pending signal, which keeps the pending signals of a thread or process a simple bit mask. Signals cannot be queued (sigqueue() is not implemented), so no value is stored in si_value.