SIGWAITINFO(2)



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

NAME
       sigwaitinfo,  sigtimedwait,  rt_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 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 inter-
       val 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
       On success, both sigwaitinfo() and sigtimedwait() return a signal  num-
       ber  (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, POSIX.1-2008.

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 sig-
       nal(7)).

       Attempts to wait for SIGKILL and SIGSTOP are silently ignored.

       If multiple threads of a process are blocked waiting for the same  sig-
       nal(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 inde-
       terminate.

       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
       sigtimedwait().

       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 pur-
       pose.  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  sig-
       timedwait() wrapper function hides these details from us, transparently
       calling rt_sigtimedwait() when the kernel provides it.

SEE ALSO
       kill(2), sigaction(2), signal(2), signalfd(2), sigpending(2),  sigproc-
       mask(2), sigqueue(3), sigsetops(3), sigwait(3), signal(7), time(7)

COLOPHON
       This  page  is  part of release 4.06 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
       https://www.kernel.org/doc/man-pages/.

Linux                             2015-07-23                    SIGWAITINFO(2)

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