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 msg_prio);

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

       int mq_timedsend(mqd_t mqdes, const char *msg_ptr,
                     size_t msg_len, unsigned 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 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 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 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),   mq_overview(7),
       time(7)

COLOPHON

       This  page  is  part  of  release 3.54 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/.