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       mq_send, mq_timedsend - send a message to a message queue


       #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)):

           _XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L


       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

       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.


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


       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.

              msg_len was greater than the mq_msgsize attribute of the message

              The call timed out before a message could be transferred.


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

       │InterfaceAttributeValue   │
       │mq_send(), mq_timedsend() │ Thread safety │ MT-Safe │


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


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


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


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