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MQ_SEND(3P) POSIX Programmer's Manual MQ_SEND(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
mq_send, mq_timedsend — send a message to a message queue (REALTIME)
#include <mqueue.h>
int mq_send(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
unsigned msg_prio);
#include <mqueue.h>
#include <time.h>
int mq_timedsend(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
unsigned msg_prio, const struct timespec *abstime);
The mq_send() function shall add the message pointed to by the
argument msg_ptr to the message queue specified by mqdes. The
msg_len argument specifies the length of the message, in bytes,
pointed to by msg_ptr. The value of msg_len shall be less than or
equal to the mq_msgsize attribute of the message queue, or mq_send()
shall fail.
If the specified message queue is not full, mq_send() shall behave as
if the message is inserted into the message queue at the position
indicated by the msg_prio argument. A message with a larger numeric
value of msg_prio shall be inserted before messages with lower values
of msg_prio. A message shall be inserted after other messages in the
queue, if any, with equal msg_prio. The value of msg_prio shall be
less than {MQ_PRIO_MAX}.
If the specified message queue is full and O_NONBLOCK is not set in
the message queue description associated with mqdes, mq_send() shall
block until space becomes available to enqueue the message, or until
mq_send() is interrupted by a signal. If more than one thread is
waiting to send when space becomes available in the message queue and
the Priority Scheduling option is supported, then the thread of the
highest priority that has been waiting the longest shall be unblocked
to send its message. Otherwise, it is unspecified which waiting
thread is unblocked. If the specified message queue is full and
O_NONBLOCK is set in the message queue description associated with
mqdes, the message shall not be queued and mq_send() shall return an
error.
The mq_timedsend() function shall add a message to the message queue
specified by mqdes in the manner defined for the mq_send() function.
However, if the specified message queue is full and O_NONBLOCK is not
set in the message queue description associated with mqdes, the wait
for sufficient room in the queue shall be terminated when the
specified timeout expires. If O_NONBLOCK is set in the message queue
description, this function shall be equivalent to mq_send().
The timeout shall expire when the absolute time specified by abstime
passes, as measured by the clock on which timeouts are based (that
is, when the value of that clock equals or exceeds abstime), or if
the absolute time specified by abstime has already been passed at the
time of the call.
The timeout shall be based on the CLOCK_REALTIME clock. The
resolution of the timeout shall be the resolution of the clock on
which it is based. The timespec argument is defined in the <time.h>
header.
Under no circumstance shall the operation fail with a timeout if
there is sufficient room in the queue to add the message immediately.
The validity of the abstime parameter need not be checked when there
is sufficient room in the queue.
Upon successful completion, the mq_send() and mq_timedsend()
functions shall return a value of zero. Otherwise, no message shall
be enqueued, the functions shall return −1, and errno shall be set to
indicate the error.
The mq_send() and mq_timedsend() functions shall fail if:
EAGAIN The O_NONBLOCK flag is set in the message queue description
associated with mqdes, and the specified message queue is
full.
EBADF The mqdes argument is not a valid message queue descriptor
open for writing.
EINTR A signal interrupted the call to mq_send() or mq_timedsend().
EINVAL The value of msg_prio was outside the valid range.
EINVAL The process or thread would have blocked, and the abstime
parameter specified a nanoseconds field value less than zero
or greater than or equal to 1000 million.
EMSGSIZE
The specified message length, msg_len, exceeds the message
size attribute of the message queue.
ETIMEDOUT
The O_NONBLOCK flag was not set when the message queue was
opened, but the timeout expired before the message could be
added to the queue.
The following sections are informative.
None.
The value of the symbol {MQ_PRIO_MAX} limits the number of priority
levels supported by the application. Message priorities range from 0
to {MQ_PRIO_MAX}−1.
None.
None.
mq_open(3p), mq_receive(3p), mq_setattr(3p), time(3p)
The Base Definitions volume of POSIX.1‐2008, mqueue.h(0p), time.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 MQ_SEND(3P)
Pages that refer to this page: mqueue.h(0p), time.h(0p), clock_getres(3p), mq_getattr(3p), mq_notify(3p), mq_open(3p), mq_receive(3p), mq_setattr(3p), mq_timedsend(3p), msgctl(3p), msgget(3p), msgrcv(3p), msgsnd(3p)