sigqueue man page on Archlinux

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

       sigqueue - queue a signal and data to a process

       #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

       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
       (either	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
       argument to the handler.	 Furthermore, the si_code field of that struc‐
       ture will be set to SI_QUEUE.

       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.

       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.

       This system call first appeared in Linux 2.2.

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


       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

       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() */

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

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2013-12-16			   SIGQUEUE(3)

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