SIGQUEUE(2)						      BSD System Calls Manual						       SIGQUEUE(2)

NAME

     sigqueue -- queue a signal to a process (REALTIME)

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <signal.h>

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

DESCRIPTION

     The sigqueue() system call causes the signal specified by signo to be sent with the value specified by value to the process specified by pid.
     If signo is zero (the null signal), error checking is performed but no signal is actually sent.  The null signal can be used to check the
     validity of PID.

     The conditions required for a process to have permission to queue a signal to another process are the same as for the kill(2) system call.
     The sigqueue() system call queues a signal to a single process specified by the pid argument.

     The sigqueue() system call returns immediately.  If the resources were available to queue the signal, the signal will be queued and sent to
     the receiving process.

     If the value of pid causes signo to be generated for the sending process, and if signo is not blocked for the calling thread and if no other
     thread has signo unblocked or is waiting in a sigwait() system call for signo, either signo or at least the pending, unblocked signal will be
     delivered to the calling thread before sigqueue() returns.  Should any multiple pending signals in the range SIGRTMIN to SIGRTMAX be selected
     for delivery, it is the lowest numbered one.  The selection order between realtime and non-realtime signals, or between multiple pending non-
     realtime signals, is unspecified.

RETURN VALUES

     Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS

     The sigqueue() system call will fail if:

     [EAGAIN]		No resources are available to queue the signal.  The process has already queued {SIGQUEUE_MAX} signals that are still
			pending at the receiver(s), or a system-wide resource limit has been exceeded.

     [EINVAL]		The value of the signo argument is an invalid or unsupported signal number.

     [EEPERM]		The process does not have the appropriate privilege to send the signal to the receiving process.

     [ESRCH]		The process pid does not exist.

SEE ALSO

     sigaction(2), sigpending(2), sigqueue(2), sigsuspend(2), sigtimedwait(2), sigwait(2), sigwaitinfo(2), pause(3), pthread_sigmask(3),
     siginfo(3)

STANDARDS

     The sigqueue() system call conforms to IEEE Std 1003.1-2004 (``POSIX.1'')

HISTORY

     Support for POSIX realtime signal queue first appeared in FreeBSD 7.0.

BSD
								 November 11, 2005							       BSD