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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  non-negative 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  (midnight
       on  the  morning  of  1  January  1970),  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 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.

       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.

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_overview(7), time(7)

COLOPHON

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       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.