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MQ_NOTIFY(2) | System Calls Manual | MQ_NOTIFY(2) |
NAME¶
mq_notify — notify process that a message is available (REALTIME)LIBRARY¶
POSIX Real-time Library (librt, -lrt)SYNOPSIS¶
#include <mqueue.h> intmq_notify(mqd_t mqdes, const struct sigevent *notification);
DESCRIPTION¶
If the argument notification is notNULL
, this system
call will register the calling process to be notified of message arrival at an
empty message queue associated with the specified message queue descriptor,
mqdes. The notification specified by the
notification argument will be sent to the process when
the message queue transitions from empty to non-empty. At any time, only one
process may be registered for notification by a message queue. If the calling
process or any other process has already registered for notification of
message arrival at the specified message queue, subsequent attempts to
register for that message queue will fail.
The notification argument points to a
sigevent structure that defines how the calling process
will be notified. If notification->sigev_notify is
SIGEV_NONE
, then no signal will be posted, but the
error status and the return status for the operation will be set
appropriately. If notification->sigev_notify is
SIGEV_SIGNAL
, then the signal specified in
notification->sigev_signo will be sent to the
process. The signal will be queued to the process and the value specified in
notification->sigev_value will be the
si_value component of the generated signal.
If notification is NULL
and the
process is currently registered for notification by the specified message
queue, the existing registration will be removed.
When the notification is sent to the registered process, its registration is
removed. The message queue then is available for registration.
If a process has registered for notification of message arrival at a message
queue and some thread is blocked in mq_receive() waiting to
receive a message when a message arrives at the queue, the arriving message
will satisfy the appropriate mq_receive(). The resulting
behavior is as if the message queue remains empty, and no notification will be
sent.
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 mq_notify() system call will fail if:- [
EBADF
] - The mqdes argument is not a valid message queue descriptor.
- [
EBUSY
] - Process is already registered for notification by the message queue.
SEE ALSO¶
mq_open(2), mq_send(2), mq_timedsend(2), siginfo(3)STANDARDS¶
The mq_notify() system call conforms to IEEE Std 1003.1-2004 (“POSIX.1”).HISTORY¶
Support for POSIX message queues first appeared in FreeBSD 7.0.COPYRIGHT¶
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html.November 29, 2005 | Debian |