mq_send(3) Library Functions Manual mq_send(3)
NAME
mq_send, mq_timedsend - send a message to a message queue
LIBRARY
Real-time library (librt, -lrt)
SYNOPSIS
#include <mqueue.h>
int mq_send(mqd_t mqdes, const char msg_ptr[.msg_len],
size_t msg_len, unsigned int msg_prio);
#include <time.h>
#include <mqueue.h>
int mq_timedsend(mqd_t mqdes, const char msg_ptr[.msg_len],
size_t msg_len, unsigned int msg_prio,
const struct timespec *abs_timeout);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
mq_timedsend():
_POSIX_C_SOURCE >= 200112L
DESCRIPTION
mq_send() adds the message pointed to by msg_ptr to the message queue
referred to by the message queue descriptor mqdes. The msg_len argu-
ment 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 pri-
ority 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. See mq_overview(7)
for details on the range for the message 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 han-
dler. If the O_NONBLOCK flag is enabled for the message queue descrip-
tion, 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 de-
scription, then abs_timeout points to a structure which specifies how
long the call will block. This value is an absolute timeout in seconds
and nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), spec-
ified in a timespec(3) structure.
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 mes-
sage queue description referred to by mqdes.
EBADF The descriptor specified in mqdes was invalid or not opened for
writing.
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.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│mq_send(), mq_timedsend() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1-2001, POSIX.1-2008.
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), timespec(3), mq_overview(7), time(7)
Linux man-pages 6.03 2022-12-15 mq_send(3)
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