|SIGQUEUE(2)||System Calls Manual||SIGQUEUE(2)|
LIBRARY¶Standard C Library (libc, -lc)
pid, int signo,
const union sigval
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.
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
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.
sigqueue() system call will fail if:
- No resources are available to queue the signal. The process has already
SIGQUEUE_MAX} signals that are still pending at the receiver(s), or a system-wide resource limit has been exceeded.
- The value of the signo argument is an invalid or unsupported signal number.
- The process does not have the appropriate privilege to send the signal to the receiving process.
- 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)
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.
sigqueueto 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.
|May 5, 2017||Linux 4.19.0-10-amd64|