SIGWAITINFO(2)            Linux Programmer's Manual           SIGWAITINFO(2)

NAME         top

       sigwaitinfo, sigtimedwait - synchronously wait for queued signals

SYNOPSIS         top

       #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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sigwaitinfo(), sigtimedwait(): _POSIX_C_SOURCE >= 199309L

DESCRIPTION         top

       sigwaitinfo() suspends execution of the calling thread until one of
       the signals in set is pending (If one of the signals in set is
       already pending for the calling thread, sigwaitinfo() will return

       sigwaitinfo() removes the signal from the set of pending signals and
       returns the signal number as its function result.  If the info
       argument is not NULL, then the buffer that it points to is used to
       return a structure of type siginfo_t (see sigaction(2)) containing
       information about the signal.

       If multiple signals in set are pending for the caller, the signal
       that is retrieved by sigwaitinfo() is determined according to the
       usual ordering rules; see signal(7) for further details.

       sigtimedwait() operates in exactly the same way as sigwaitinfo()
       except that it has an additional argument, timeout, which specifies
       the interval for which the thread is suspended waiting for a signal.
       (This interval will be rounded up to the system clock granularity,
       and kernel scheduling delays mean that the interval may overrun by a
       small amount.)  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         top

       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         top

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

       EINTR  The wait was interrupted by a signal handler; see signal(7).
              (This handler was for a signal other than one of those in

       EINVAL timeout was invalid.

CONFORMING TO         top


NOTES         top

       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 become pending 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, in order to prevent the
       signal being treated according to its default disposition in a thread
       other than the one calling sigwaitinfo() or sigtimedwait()).

       The set of signals that is pending for a given thread is the union of
       the set of signals that is pending specifically for that thread and
       the set of signals that is pending for the process as a whole (see

       Attempts to wait for SIGKILL and SIGSTOP are silently ignored.

       If multiple threads of a process are blocked waiting for the same
       signal(s) in sigwaitinfo() or sigtimedwait(), then exactly one of the
       threads will actually receive the signal if it becomes pending for
       the process as a whole; which of the threads receives the signal is

       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.

   C library/kernel ABI differences
       On Linux, sigwaitinfo() is a library function implemented on top of

       The raw sigtimedwait() system call has a fifth argument, size_t
       sigsetsize, which specifies the size in bytes of the set argument.
       The glibc sigtimedwait() wrapper function specifies this argument as
       a fixed value (equal to sizeof(sigset_t)).

SEE ALSO         top

       kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2),
       sigprocmask(2), sigqueue(3), sigsetops(3), sigwait(3), signal(7),

COLOPHON         top

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Linux                            2014-08-19                   SIGWAITINFO(2)