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



NAME
       sigqueue, rt_sigqueueinfo - 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 (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.  Fur-
       thermore, the si_code field of that structure will be set to SI_QUEUE.

RETURN VALUE
       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.

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.

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 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() */

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

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2007-07-26                                                SIGQUEUE(2)