mq_notify(3) [osf1 man page]
mq_notify(3) Library Functions Manual mq_notify(3) NAME
mq_notify - Attaches a request for asynchronous signal notification to a message queue (P1003.1b) LIBRARY
Realtime Library (librt.so, librt.a) SYNOPSIS
#include <mqueue.h> int mq_notify ( mqd_t mqdes, const struct sigevent *notification); PARAMETERS
mqdes Specifies a message queue descriptor. *notification Specifies a signal to be sent when the specified queue accepts a message. If the notification argument is NULL, and the process has previously attached a notification request to the message queue with this mqdes argument, the notification request is detached and the queue is available for another process to attach a notification request. DESCRIPTION
The mq_notify function attaches a request for asynchronous signal notification to a message queue for the calling process. Following a call to this function, the specified signal is sent to the calling process when the queue transitions from empty to non-empty. Two or more processes cannot attach notification requests to the same queue at the same time. If a process has attached a notification request and any process is blocked in the execution of the mq_receive function waiting to receive a message when a message arrives at the queue, then the appropriate mq_receive function is completed and the notification remains pending. When the notification has been sent, the registration is canceled. In effect, it is a one-shot notification and must be re-registered if required. Note that the POSIX IPC functions are not reentrant with respect to signals. For example, if your application were to use a signal to notify it that a queue has become non-empty and then attempt to call mq_receive from the signal handler, the signal handler must reside in a thread other than the tread that called mq_send. Otherwise, a deadlock on internal locks would occur. RETURN VALUES
On successful completion, the function returns the value 0 (zero); otherwise, the function returns the value -1 and sets errno to indicate the error. ERRORS
The mq_notify function fails under the following conditions: [EBADF] The mqdes argument is not a valid message queue descriptor. [EBUSY] A process has already attached to this message queue for asynchronous notification, or the calling process attempted to can- cel a request that was attached by another process. [EINVAL] The requested signo is invalid, or the sigev_notify field of the notification structure does not equal SIGEV_SIGNAL. RELATED INFORMATION
Functions: mq_open(3), mq_send(3) Guide to Realtime Programming delim off mq_notify(3)
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mq_notify(3RT) Realtime Library Functions mq_notify(3RT) NAME
mq_notify - notify process (or thread) that a message is available on a queue SYNOPSIS
cc [ flag... ] file... -lrt [ library... ] #include <mqueue.h> int mq_notify(mqd_t mqdes, const struct sigevent *notification); DESCRIPTION
The mq_notify() function provides an asynchronous mechanism for processes to receive notice that messages are available in a message queue, rather than synchronously blocking (waiting) in mq_receive(3RT). If notification is not NULL, this function registers the calling process to be notified of message arrival at an empty message queue asso- ciated with the message queue descriptor, mqdes. The notification specified by notification 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 specific message queue. If the calling process or any other process has already registered for notification of message arrival at the specified message queue, subse- quent attempts to register for that message queue will fail. The notification argument points to a structure that defines both the signal to be generated and how the calling process will be notified upon I/O completion. If notification->sigev_notify is SIGEV_NONE, then no signal will be posted upon I/O completion, 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. If the SA_SIGINFO flag is set for that signal number, then 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 (see sig- info.h(3HEAD)). If notification is NULL and the process is currently registered for notification by the specified message queue, the existing registration is removed. The message queue is then available for future registration. When the notification is sent to the registered process, its registration is removed. The message queue is then be available for registra- tion. If a process has registered for notification of message arrival at a message queue and some processes is blocked in mq_receive(3RT) waiting to receive a message when a message arrives at the queue, the arriving message will be received by the appropriate mq_receive(3RT), and no notification will be sent to the registered process. The resulting behavior is as if the message queue remains empty, and this notification will not be sent until the next arrival of a message at this queue. Any notification registration is removed if the calling process either closes the message queue or exits. RETURN VALUES
Upon successful completion, mq_notify() returns 0; otherwise, it returns -1 and sets errno to indicate the error. ERRORS
The mq_notify() function will fail if: EBADF The mqdes argument is not a valid message queue descriptor. EBUSY A process is already registered for notification by the message queue. ENOSYS The mq_notify() function is not supported by the system. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
mqueue.h(3HEAD), siginfo.h(3HEAD), signal.h(3HEAD), mq_close(3RT), mq_open(3RT), mq_receive(3RT), mq_send(3RT), attributes(5), standards(5) NOTES
Solaris 2.6 was the first release to support the Asynchronous Input and Output option. Prior to this release, this function always returned -1 and set errno to ENOSYS. SunOS 5.10 28 Jun 2002 mq_notify(3RT)