NAME
sigqueue —
queue a signal to a process
(REALTIME)
LIBRARY
library “libc”
SYNOPSIS
#include
<signal.h>
int
sigqueue(pid_t
pid, int signo,
const union sigval
value);
DESCRIPTION
Thesigqueue()
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.
- [
EPERM] - 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
kill(2), sigaction(2), sigpending(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.
CAVEATS
When using sigqueue to send signals to a
process which might have a different ABI (for instance, one is 32-bit and
the other 64-bit), the sival_int member of
value can be delivered reliably, but the
sival_ptr may be truncated in endian dependent ways
and must not be relied on. Further, many pointer integrity schemes disallow
sending pointers to other processes, and this technique should not be used
in programs intended to be portable.