SIGQUEUE(3C) Standard C Library Functions SIGQUEUE(3C)

NAME

sigqueue - queue a signal to a process

SYNOPSIS

#include <sys/types.h>
#include <signal.h>

int sigqueue(pid_t pid, int signo, const union sigval value);

DESCRIPTION

The sigqueue() function causes the signal specified by signo to be
sent with the value specified by value to the process specified by
pid. If signo is 0 (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) function.


The sigqueue() function returns immediately. If SA_SIGINFO is set for
signo and if the resources were available to queue the signal, the
signal is queued and sent to the receiving process. If SA_SIGINFO is
not set for signo, then signo is sent at least once to the receiving
process; it is unspecified whether value will be sent to the
receiving process as a result of this call.


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(2)
function for signo, either signo or at least the pending, unblocked
signal will be delivered to the calling thread before the sigqueue()
function returns. Should any of multiple pending signals in the range
SIGRTMIN to SIGRTMAX be selected for delivery, it will be 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 specified signal will have been
queued, and the sigqueue() function returns 0. Otherwise, the
function returns -1 and sets errno to indicate the error.

ERRORS

The sigqueue() function 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 signo is an invalid or unsupported signal
number.


ENOSYS
The sigqueue() function is not supported by the system.


EPERM
The process does not have the appropriate privilege to
send the signal to the receiving process.


ESRCH
The process pid does not exist.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+

SEE ALSO

kill(2), sigwaitinfo(3C), siginfo.h(3HEAD), signal.h(3HEAD),
attributes(7), standards(7)

February 5, 2008 SIGQUEUE(3C)