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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 delivered.  (If one
       of the signals in set is already pending for the calling thread, sigwaitinfo()  will  return  immediately  with
       information about that signal.)

       sigwaitinfo() removes the delivered signal from the set 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  sigac-
       tion(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 thread is suspended.   This  argu-
       ment 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; 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 are delivered between successive calls to sigwait-
       info()  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()).

       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)).

       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 is delivered to 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(2), sigsetops(3), sig-
       wait(3), signal(7), time(7)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-10-04                    SIGWAITINFO(2)