mq_timedsend(), mq_timedsend_monotonic()

Send a message to a message queue

Synopsis:

#include <mqueue.h>
#include <time.h>

int mq_timedsend( mqd_t mqdes, 
                  const char * msg_ptr, 
                  size_t msg_len, 
                  unsigned int msg_prio,
                  const struct timespec * abs_timeout );

int mq_timedsend_monotonic(
                  mqd_t mqdes, 
                  const char * msg_ptr, 
                  size_t msg_len, 
                  unsigned int msg_prio,
                  const struct timespec * abs_timeout );

Arguments:

mqdes

The descriptor of the message queue you want to put the message into, returned by mq_open().

msg_ptr

A pointer to the message data.

msg_len

The size of the buffer, in bytes.

msg_prio

The priority of the message, in the range from 0 to (MQ_PRIO_MAX-1).

abs_timeout

A pointer to a timespec structure that specifies the absolute time (not the relative time to the current time) to wait before the function stops trying to receive messages.

Library:

• For the traditional implementation, libc

  Use the -l c option to qcc to link against this library. This library is usually included automatically.

• For the alternate implementation using asynchronous messages, libmq

  Use the -l mq option to qcc to link against this library.

Description:

The mq_timedsend() function puts a message of size msg_len and pointed to by msg_ptr into the queue indicated by mqdes. The new message has a priority of msg_prio. The mq_timedsend_monotonic() function is a QNX Neutrino extension; it's similar to mq_timedsend(), but it uses CLOCK_MONOTONIC, so the timeout isn't affected by changes to the system time.

---

Neutrino supports two implementations of message queues: a traditional implementation, and an alternate one that uses asynchronous messages. For more information, see the entries for mq and mqueue in the Utilities Reference, as well as the Managing POSIX Message Queues technote.

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The queue maintained is in priority order, and in FIFO order within the same priority.

If the number of elements on the specified queue is equal to its mq_maxmsg, and and O_NONBLOCK wasn't set (in the oflag argument to mq_open()), the call to mq_timedsend() blocks. It becomes unblocked when there's room on the queue to send the given message. If more than one mq_timedsend() is blocked on a given queue, and space becomes available in that queue to send, then the mq_timedsend() with the highest priority message is unblocked.

In the traditional (mqueue) implementation, calling write() with mqdes is analogous to calling mq_timedsend() with a msg_prio of 0.

Returns:

-1 if an error occurred (errno is set). Any other value indicates success.

Errors:

EAGAIN

The O_NONBLOCK flag was set when opening the queue, and the specified queue is full.

EBADF

The mqdes argument doesn't represent a valid message queue descriptor, or mqdes isn't opened for writing.

EINTR

The call was interrupted by a signal.

EINVAL

One of the following is true:

• The msg_len is negative.
• The msg_prio is greater than (MQ_PRIO_MAX-1).
• The msg_prio is less than 0.
• The MQ_PRIO_RESTRICT flag is set in the mq_attr member of mqdes, and msg_prio is greater than the priority of the calling process.
• The process or thread would have blocked, and the abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.

EMSGSIZE

The msg_len argument is greater than the msgsize associated with the specified queue.

ETIMEDOUT

The timeout value was exceeded.

Examples:

See the example for mq_timedreceive().

Classification:

mq_timedsend() is POSIX 1003.1 MSG; mq_timedsend_monotonic() is QNX Neutrino

See also:

mq_close(), mq_open(), mq_receive(), mq_send(), mq_timedreceive(), timespec

mq, mqueue in the Utilities Reference

Managing POSIX Message Queues technote.