mq_send, mq_timedsend - send a message to a message queue
Real-time library (
librt,
-lrt)
#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);
mq_timedsend():
_POSIX_C_SOURCE >= 200112L
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 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. 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 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 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),
specified 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.
On success,
mq_send() and
mq_timedsend() return zero; on error, -1
is returned, with
errno set to indicate the error.
- 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 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.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
mq_send (), mq_timedsend () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008.
On Linux,
mq_timedsend() is a system call, and
mq_send() is a
library function layered on top of that system call.
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)