MQ_SEND(3)                                          Linux Programmer's Manual                                         MQ_SEND(3)



NAME
       mq_send, mq_timedsend - send a message to a message queue

SYNOPSIS
       #include <mqueue.h>

       mqd_t mq_send(mqd_t mqdes, const char *msg_ptr,
                     size_t msg_len, unsigned msg_prio);

       #define _XOPEN_SOURCE 600
       #include <time.h>
       #include <mqueue.h>

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

       Link with -lrt.

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 immedi-
       ately.

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 empty, 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_over-
       view(7), time(7)

COLOPHON
       This page is part of release 3.25 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/.



Linux                                                      2010-02-25                                                 MQ_SEND(3)