MQ_SEND
Section: Linux Programmer's Manual (3)
Updated: 2010-09-20
NAME
mq_send, mq_timedsend - send a message to a message queue
SYNOPSIS
#include <mqueue.h>
int mq_send(mqd_t mqdes, const char *msg_ptr,
size_t msg_len, unsigned msg_prio);
#include <time.h>
#include <mqueue.h>
int mq_timedsend(mqd_t mqdes, const char *msg_ptr,
size_t msg_len, unsigned msg_prio,
const struct timespec *abs_timeout);
Link with -lrt.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
mq_timedsend():
-
_XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L
DESCRIPTION
mq_send()
adds the message pointed to by
msg_ptr
to the message queue referred to by the descriptor
mqdes.
The
msg_len
argument specifies the length of the message pointed to by
msg_ptr;
this length must be less than or equal to the queue's
mq_msgsize
attribute.
Zero-length messages are allowed.
The
msg_prio
argument is a nonnegative integer that specifies the priority
of this message.
Messages are placed on the queue in decreasing order of priority,
with newer messages of the same priority being placed after
older messages with the same priority.
If the message queue is already full
(i.e., the number of messages on the queue equals the queue's
mq_maxmsg
attribute), then, by default,
mq_send()
blocks until sufficient space becomes available to allow the message
to be queued, or until the call is interrupted by a signal handler.
If the
O_NONBLOCK
flag is enabled for the message queue description,
then the call instead fails immediately with the error
EAGAIN.
mq_timedsend()
behaves just like
mq_send(),
except that if the queue is full and the
O_NONBLOCK
flag is not enabled for the message queue description, then
abs_timeout
points to a structure which specifies a ceiling on the time for which
the call will block.
This ceiling is an absolute timeout in seconds and nanoseconds
since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), and it is
specified in the following structure:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
If the message queue is full,
and the timeout has already expired by the time of the call,
mq_timedsend()
returns immediately.
RETURN VALUE
On success,
mq_send()
and
mq_timedsend()
return zero; on error, -1 is returned, with
errno
set to indicate the error.
ERRORS
- EAGAIN
-
The queue was full, and the
O_NONBLOCK
flag was set for the message queue description referred to by
mqdes.
- EBADF
-
The descriptor specified in
mqdes
was invalid.
- EINTR
-
The call was interrupted by a signal handler; see
signal(7).
- EINVAL
-
The call would have blocked, and
abs_timeout
was invalid, either because
tv_sec
was less than zero, or because
tv_nsec
was less than zero or greater than 1000 million.
- EMSGSIZE
-
msg_len
was greater than the
mq_msgsize
attribute of the message queue.
- ETIMEDOUT
-
The call timed out before a message could be transferred.
CONFORMING TO
POSIX.1-2001.
NOTES
On Linux,
mq_timedsend()
is a system call, and
mq_send()
is a library function layered on top of that system call.
SEE ALSO
mq_close(3),
mq_getattr(3),
mq_notify(3),
mq_open(3),
mq_receive(3),
mq_unlink(3),
feature_test_macros(7),
mq_overview(7),
time(7)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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Time: 07:34:53 GMT, March 26, 2013