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SIGQUEUE(3)		   Linux Programmer's Manual		   SIGQUEUE(3)

NAME
       sigqueue	- queue	a signal and data to a process

SYNOPSIS
       #include	<signal.h>

       int sigqueue(pid_t pid, int sig,	const union sigval value);

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

       sigqueue(): _POSIX_C_SOURCE >= 199309L

DESCRIPTION
       sigqueue()  sends  the signal specified in sig to the process whose PID
       is given	in pid.	 The permissions required to send  a  signal  are  the
       same  as	for kill(2).  As with kill(2), the null	signal (0) can be used
       to check	if a process with a given PID exists.

       The value argument is used to specify an	accompanying item of data (ei-
       ther an integer or a pointer value) to be sent with the signal, and has
       the following type:

	   union sigval	{
	       int   sival_int;
	       void *sival_ptr;
	   };

       If the receiving	process	has installed a	handler	for this signal	 using
       the  SA_SIGINFO	flag to	sigaction(2), then it can obtain this data via
       the si_value field of the siginfo_t structure passed as the second  ar-
       gument  to  the handler.	 Furthermore, the si_code field	of that	struc-
       ture will be set	to SI_QUEUE.

RETURN VALUE
       On success, sigqueue() returns 0, indicating that the signal  was  suc-
       cessfully  queued  to the receiving process.  Otherwise,	-1 is returned
       and errno is set	to indicate the	error.

ERRORS
       EAGAIN The limit	of signals which may be	queued has been	reached.  (See
	      signal(7)	for further information.)

       EINVAL sig was invalid.

       EPERM  The  process  does not have permission to	send the signal	to the
	      receiving	process.  For the required permissions,	see kill(2).

       ESRCH  No process has a PID matching pid.

VERSIONS
       This system call	first appeared in Linux	2.2.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The sigqueue() function is thread-safe.

CONFORMING TO
       POSIX.1-2001.

NOTES
       If this function	results	in the sending of a signal to the process that
       invoked	it, and	that signal was	not blocked by the calling thread, and
       no other	threads	were willing to	handle this signal (either  by	having
       it  unblocked,  or  by  waiting for it using sigwait(3)), then at least
       some signal must	be delivered to	this thread before this	 function  re-
       turns.

       On  Linux,  this	 function  is implemented using	the rt_sigqueueinfo(2)
       system call.  The system	call differs in	its third argument,  which  is
       the  siginfo_t  structure  that	will  be  supplied  to	the  receiving
       process's signal	handler	or returned by the  receiving  process's  sig-
       timedwait(2) call.  Inside the glibc sigqueue() wrapper,	this argument,
       uinfo, is initialized as	follows:

	   uinfo.si_signo = sig;      /* Argument supplied to sigqueue() */
	   uinfo.si_code = SI_QUEUE;
	   uinfo.si_pid	= getpid();   /* Process ID of sender */
	   uinfo.si_uid	= getuid();   /* Real UID of sender */
	   uinfo.si_value = val;      /* Argument supplied to sigqueue() */

SEE ALSO
       kill(2),	      rt_sigqueueinfo(2),	sigaction(2),	    signal(2),
       pthread_sigqueue(3), sigwait(3),	signal(7)

COLOPHON
       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
       http://www.kernel.org/doc/man-pages/.

Linux				  2013-12-16			   SIGQUEUE(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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