redhat man page for sigqueue

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

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);

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.	Furthermore, 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 proces.  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.

       ESRCH  No process has a PID matching pid.

       EPERM  The process does not have permission to send the signal to the receiving process.  (See kill(2) for further information.)

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.

CONFORMING TO
       POSIX 1003.1-2001

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

Linux 2.4.18							    2002-06-07							       SIGQUEUE(2)