SIGWAITINFO(2)						     Linux Programmer's Manual						    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);

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

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

DESCRIPTION

       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 immediately.)

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

       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 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 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 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 signal(7)).

       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
       indeterminate.

       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.

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

SEE ALSO

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

COLOPHON

       This page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2012-07-21							    SIGWAITINFO(2)