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 sig-
       nals 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  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 thread is suspended.  This argument is of the follow-
       ing 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 sigwaitinfo() or sigtimed-
       wait()) 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 sigtimed-
       wait()).

       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 possibil-
       ity 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), sigwait(3), sig-
       nal(7), time(7)

COLOPHON
       This  page  is  part of release 3.25 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                                                      2008-10-04                                             SIGWAITINFO(2)