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

       sigwaitinfo, sigtimedwait - synchronously wait for queued signals

       #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

       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  or-
       dering 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 in-
       terval 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.

       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.

       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.


       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-

       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-

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

       The raw sigtimedwait() system call has a	fifth argument,	size_t sigset-
       size, which specifies the size in bytes of the set argument.  The glibc
       sigtimedwait()  wrapper	function  specifies  this  argument as a fixed
       value (equal to sizeof(sigset_t)).

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

       This  page  is  part of release 3.74 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				  2014-08-19			SIGWAITINFO(2)


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