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

NAME         top

       mq_send, mq_timedsend - send a message to a message queue

SYNOPSIS         top

       #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)):

           _POSIX_C_SOURCE >= 200112L

DESCRIPTION         top

       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.

       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 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         top

       On success, mq_send() and mq_timedsend() return zero; on error, -1 is
       returned, with errno set to indicate the error.

ERRORS         top

       EAGAIN The queue was full, and the O_NONBLOCK flag was set for the
              message queue description referred to by mqdes.

       EBADF  The file 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.

              msg_len was greater than the mq_msgsize attribute of the
              message queue.

              The call timed out before a message could be transferred.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                 Attribute     Value   │
       │mq_send(), mq_timedsend() │ Thread safety │ MT-Safe │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

NOTES         top

       On Linux, mq_timedsend() is a system call, and mq_send() is a library
       function layered on top of that system call.

SEE ALSO         top

       mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_receive(3),
       mq_unlink(3), mq_overview(7), time(7)

COLOPHON         top

       This page is part of release 4.08 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

Linux                            2016-03-15                       MQ_SEND(3)