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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017, mqueue.h(0p),
time.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 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)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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