MQ_SEND(3P) POSIX Programmer's Manual MQ_SEND(3P)PROLOG
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.
NAME
mq_send, mq_timedsend — send a message to a message queue (REALTIME)
SYNOPSIS
#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);
DESCRIPTION
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 indi‐
cated 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 wait‐
ing 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.
RETURN VALUE
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.
ERRORS
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 param‐
eter 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.
EXAMPLES
None.
APPLICATION USAGE
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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOmq_open(), mq_receive(), mq_setattr(), time()
The Base Definitions volume of POSIX.1‐2008, <mqueue.h>, <time.h>
COPYRIGHT
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 Electri‐
cal 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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 MQ_SEND(3P)
