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)