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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>
int
mq_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¶
Themq_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¶
Themq_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 |