05-10-2011
Read about the POSIX signal interface.
posix signal - Google Search
In general, sending the same signal repeatedly to a server process is not a great idea. You should use IPC (pipes, sockets, message queues, lockfiles, etc.) instead.
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LEARN ABOUT NETBSD
sigqueue
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);
int
sigqueueinfo(pid_t pid, const siginfo_t *info);
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 is implemented using sigqueueinfo() and passing the appropriate information in the info 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.
[EEPERM] The process does not have the appropriate privilege to send the signal to the receiving process.
[EINVAL] The value of the signo argument is an invalid or unsupported signal number.
[ESRCH] The process pid does not exist.
SEE ALSO
sigaction(2), siginfo(2), sigpending(2), sigsuspend(2), sigtimedwait(2), sigwait(2), sigwaitinfo(2), pause(3), pthread_sigmask(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 NetBSD 6.0.
BSD
January 9, 2011 BSD