SIGQUEUE(2)

SIGQUEUE(2) | System Calls Manual | SIGQUEUE(2)

# NAME

`sigqueue`, `sigqueueinfo` —
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.
[`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

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.

January 9, 2011 | NetBSD 10.1