PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

MQ_SEND(3P)               POSIX Programmer's Manual              MQ_SEND(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

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

SYNOPSIS         top

       #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 *abstime);

DESCRIPTION         top

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

       The timeout shall be based on the CLOCK_REALTIME clock.  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 abstime parameter need not be checked when there
       is sufficient room in the queue.

RETURN VALUE         top

       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         top

       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 abstime
              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         top

       None.

APPLICATION USAGE         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       mq_open(3p), mq_receive(3p), mq_setattr(3p), time(3p)

       The Base Definitions volume of POSIX.1‐2008, mqueue.h(0p), time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                         MQ_SEND(3P)