notify process that a message is available
POSIX Real-time Library (librt, -lrt)
struct sigevent *notification
If the argument notification is not
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
. 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.
argument points to a
structure that defines how the
calling process will be notified. If
, then no signal will be posted,
but the error status and the return status for the operation will be set
notifications, the signal
specified in notification->sigev_signo
will be sent to the calling process
) or to the thread whose LWP ID
). The information for the
queued signal will include:
||the value stored in
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
() waiting to receive a message
when a message arrives at the queue, the arriving message will satisfy the
(). The resulting
behavior is as if the message queue remains empty, and no notification will be
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable
is set to indicate the error.
() system call will fail if:
- The mqdes argument is not a valid message
- Process is already registered for notification by the message queue.
- The asynchronous notification method in
notification->sigev_notify is invalid
or not supported.
() system call conforms to
IEEE Std 1003.1-2004
Support for POSIX message queues first appeared in FreeBSD
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