SIGWAITINFO(2)

NAME
sigwaitinfo, sigtimedwait - synchronously wait for queued signals

SYNOPSIS
#include <signal.h>

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

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

DESCRIPTION
sigwaitinfo() suspends execution of the calling process until one of the signals in set is delivered. (If one of the signals in set is already pending for the calling process, sigwaitinfo() will return immediately with information about that signal.) sigwaitinfo() removes the delivered signal from the calling process's list of pending signals and returns the signal number as its function result. If the info argument is not NULL, then it returns a structure of type siginfo_t (see sigaction(2)) containing information about the signal.

Signals returned via sigwaitinfo() are delivered in the usual order; see signal(7) for further details.

sigtimedwait() operates in exactly the same way as sigwaitinfo() except that it has an additional argument, timeout, which enables an upper bound to be placed on the time for which the process is suspended. This argument is of the following type:

struct timespec {
    long    tv_sec;         /* seconds */
    long    tv_nsec;        /* nanoseconds */
}

If both fields of this structure are specified as 0, a poll is performed: sigtimedwait() returns immediately, either with information about a signal that was pending for the caller, or with an error if none of the signals in set was pending.

RETURN VALUE
On success, both sigwaitinfo() and sigtimedwait() return a signal number (i.e., a value greater than zero). On failure both calls return -1, with errno set to indicate the error.

ERRORS

EAGAIN
    No signal in set was delivered within the timeout period specified to sigtimedwait().

EINTR
    The wait was interrupted by a signal handler. (This handler was for a signal other than one of those in set.)

EINVAL
    timeout was invalid.

CONFORMING TO
POSIX.1-2001

NOTES
In normal usage, the calling program blocks the signals in set via a prior call to sigprocmask(2) (so that the default disposition for these signals does not occur if they are delivered between successive calls to sigwaitinfo() or sigtimedwait()) and does not establish handlers for these signals. In a multithreaded program, the signal should be blocked in all threads to prevent the signal being delivered to a thread other than the one calling sigwaitinfo() or sigtimedwait()).

POSIX leaves the meaning of a NULL value for the timeout argument of sigtimedwait() unspecified, permitting the possibility that this has the same meaning as a call to sigwaitinfo(), and indeed this is what is done on Linux.

SEE ALSO
kill(2), sigaction(2), signal(2), sigpending(2), sigprocmask(2), sigqueue(2), sigsetops(3), signal(7)