sigtimedwait(2) — Linux manual page


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

NAME         top

       sigwaitinfo,  sigtimedwait,  rt_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 per‐
       formed: 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

       POSIX.1-2001, POSIX.1-2008.

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

       sigwaitinfo() or sigtimedwait(), can't be used to receive signals
       that are synchronously generated, such as the SIGSEGV signal that
       results from accessing an invalid memory address or the SIGFPE signal
       that results from an arithmetic error.  Such signals can be caught
       only via signal handler.

       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 differences
       On Linux, sigwaitinfo() is a library function implemented on top of

       The glibc wrapper functions for sigwaitinfo() and sigtimedwait()
       silently ignore attempts to wait for the two real-time signals that
       are used internally by the NPTL threading implementation.  See
       nptl(7) for details.

       The original Linux system call was named sigtimedwait().  However,
       with the addition of real-time signals in Linux 2.2, the fixed-size,
       32-bit sigset_t type supported by that system call was no longer fit
       for purpose.  Consequently, a new system call, rt_sigtimedwait(), was
       added to support an enlarged sigset_t type.  The new system call
       takes a fourth argument, size_t sigsetsize, which specifies the size
       in bytes of the signal set in set.  This argument is currently
       required to have the value sizeof(sigset_t) (or the error EINVAL
       results).  The glibc sigtimedwait() wrapper function hides these
       details from us, transparently calling rt_sigtimedwait() when the
       kernel provides it.

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

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2017-09-15                   SIGWAITINFO(2)

Pages that refer to this page: sigqueue(3)sigwait(3)nptl(7)signal(7)time(7)