NAME

       mq_send, mq_timedsend - send a message to a message queue (REALTIME)

SYNOPSIS

       #include <mqueue.h>

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

       #include <mqueue.h>
       #include <time.h>
       int mq_timedsend(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
              unsigned msg_prio, const struct timespec *abs_timeout);

DESCRIPTION

       The  mq_send()  function  shall  add the message pointed to by the argument msg_ptr to the
       message queue specified by mqdes.  The  msg_len  argument  specifies  the  length  of  the
       message, in bytes, pointed to by msg_ptr. The value of msg_len shall be less than or equal
       to the mq_msgsize attribute of the message queue, or mq_send() shall fail.

       If the specified message queue is not full, mq_send() shall behave as if  the  message  is
       inserted  into  the  message  queue  at the position indicated by the msg_prio argument. A
       message with a larger numeric value of msg_prio shall be  inserted  before  messages  with
       lower  values  of msg_prio. A message shall be inserted after other messages in the queue,
       if any, with equal msg_prio. The value of msg_prio shall be less than {MQ_PRIO_MAX}.

       If the specified message queue is full and O_NONBLOCK is not  set  in  the  message  queue
       description  associated with mqdes, mq_send() shall block until space becomes available to
       enqueue the message, or until mq_send() is interrupted by  a  signal.  If  more  than  one
       thread  is  waiting  to  send  when  space  becomes available in the message queue and the
       Priority Scheduling option is supported, then the thread of the highest priority that  has
       been  waiting  the  longest  shall  be  unblocked  to  send  its message. Otherwise, it is
       unspecified which waiting thread is unblocked.  If the specified message queue is full and
       O_NONBLOCK  is  set  in  the  message queue description associated with mqdes, the message
       shall not be queued and mq_send() shall return an error.

       The mq_timedsend() function shall add a message to the message queue specified by mqdes in
       the  manner defined for the mq_send() function. However, if the specified message queue is
       full and O_NONBLOCK is not set in the message queue description associated with mqdes, the
       wait  for  sufficient  room  in  the  queue shall be terminated when the specified timeout
       expires. If O_NONBLOCK is set in the message queue description,  this  function  shall  be
       equivalent to mq_send().

       The  timeout  shall  expire  when  the  absolute  time specified by abs_timeout passes, as
       measured by the clock on which timeouts are based (that is, when the value of  that  clock
       equals  or  exceeds  abs_timeout),  or  if  the absolute time specified by abs_timeout has
       already been passed at the time of the call.

       If the Timers option is supported, the timeout shall be based on the CLOCK_REALTIME clock;
       if  the  Timers option is not supported, the timeout shall be based on the system clock as
       returned by the time() function.

       The resolution of the timeout shall be the resolution of the clock on which it  is  based.
       The timespec argument is defined in the <time.h> header.

       Under  no circumstance shall the operation fail with a timeout if there is sufficient room
       in the queue to add the message immediately. The validity  of  the  abs_timeout  parameter
       need not be checked when there is sufficient room in the queue.

RETURN VALUE

       Upon  successful  completion, the mq_send()    and mq_timedsend() functions shall return a
       value of zero. Otherwise, no message shall be enqueued, the functions shall return -1, and
       errno shall be set to indicate the error.

ERRORS

       The mq_send()    and mq_timedsend() functions shall fail if:

       EAGAIN The  O_NONBLOCK flag is set in the message queue description associated with mqdes,
              and the specified message queue is full.

       EBADF  The mqdes argument is not a valid message queue descriptor open for writing.

       EINTR  A signal interrupted the call to mq_send()    or mq_timedsend().

       EINVAL The value of msg_prio was outside the valid range.

       EINVAL The process or thread would have blocked, and the abs_timeout parameter specified a
              nanoseconds field value less than zero or greater than or equal to 1000 million.

       EMSGSIZE
              The  specified  message  length, msg_len, exceeds the message size attribute of the
              message queue.

       ETIMEDOUT
              The O_NONBLOCK flag was not set when the message queue was opened, but the  timeout
              expired before the message could be added to the queue.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The  value  of  the symbol {MQ_PRIO_MAX} limits the number of priority levels supported by
       the application. Message priorities range from 0 to {MQ_PRIO_MAX}-1.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       mq_open()  ,  mq_receive()  ,  mq_setattr()  ,  mq_timedreceive()  ,  time()  ,  the  Base
       Definitions volume of IEEE Std 1003.1-2001, <mqueue.h>, <time.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .