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

       sigqueue, rt_sigqueueinfo - 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 structure will be set to SI_QUEUE.

       On success, sigqueue() returns 0, indicating that the signal was successfully 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 per-
              missions, see kill(2).

       ESRCH  No process has a PID matching pid.

       This system call first appeared in Linux 2.2.


       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 returns.

       On  Linux,  the  underlying system call is actually named rt_sigqueueinfo(), and 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  sigtimedwait(2)  call.  Inside the glibc sigqueue() wrapper, this argument, info, is
       initialized as follows:

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

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

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2007-07-26                       SIGQUEUE(2)