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>

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

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

       int mq_timedsend(mqd_t mqdes, const char *msg_ptr,
                     size_t msg_len, unsigned int 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  mes‐
       sage.   Messages  are placed on the queue in decreasing order of priority, with newer mes‐
       sages 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  descrip‐
              tion 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.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The mq_send() and mq_timedsend() functions are thread-safe.

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),
       mq_overview(7), time(7)

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-06-03                                 MQ_SEND(3)