Wait for a signal or a timeout


#include <signal.h>

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


A set of signals from which the function selects a pending signal.
NULL, or a pointer to a siginfo_t structure where the function can store information about the signal.
NULL, or a pointer to a timespec structure that specifies the maximum time to wait for a pending signal.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The sigtimedwait() function selects a pending signal from set, atomically clears it from the set of pending signals in the process, and returns that signal number.

If the info argument isn't NULL, sigtimedwait() stores the selected signal in the si_signo member of info, and the cause of the signal in the si_code member.

If any value is queued to the selected signal, the first 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 resources used to queue the signal are 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 is reset.

If none of the signals specified by set are pending, sigtimedwait() waits for the time interval specified by the timespec structure timeout. The CLOCK_MONOTONIC clock is used to measure the time interval.

If timeout is zero and if none of the signals specified by set are pending, then sigtimedwait() returns immediately with an error. If timeout is NULL, sigtimedwait() behaves the same as sigwaitinfo().


The selected signal number, or -1 if an error occurred (errno is set).


The timeout expired before a signal specified in set was generated, or all kernel timers are in use.
A fault occurred while accessing the provided buffers.
The wait was interrupted by an unblocked, caught signal.
The timeout argument specified a tv_nsec value less than zero or greater than or equal to 1000 million or set contains an invalid or unsupported signal number.


POSIX 1003.1 RTS

Cancellation point Yes
Interrupt handler No
Signal handler Yes
Thread Yes