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Name

sigqueue - queue a signal to a process

Synopsis

cc [ flag ... ] file ... -lposix4 [ library ... ]

#include <signal.h>

int sigqueue(pid_t pid, int signo,

const union sigval value);

union sigval {
   int    sival_int;    /* integer value */

   void    *sival_ptr;    /* pointer value */

};

MT-Level

Async-Signal-Safe

Description

sigqueue() causes the signal, signo to be sent with the value, value to the process, 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 kill(2) .

If resources were not available to queue the signal, sigqueue() exits and returns immediately. If SA_SIGINFO is set for signo in the receiving process, and if the resources were available, the signal is left queued and pending. If SA_SIGINFO is not set for signo, then signo is sent at least once to the receiving process.

If the value of pid causes signo to be generated for the sending process, and if signo is not blocked, either signo or at least the pending, unblocked signal with the lowest number will be delivered to the sending process before sigqueue() returns.

Return Values

If successful, sigqueue() returns 0, and queues the specified signal. Otherwise, sigqueue() returns -1 and sets errno to indicate the error condition.

Errors

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 signo is an invalid or unsupported signal number.
ENOSYS
sigqueue() is not supported by this implementation.
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) , sigwaitinfo(3R) , siginfo(5) , signal(5)

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