mq_send(3p) — Linux manual page

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.1‐2017, mqueue.h(0p),
       time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                       MQ_SEND(3P)

Pages that refer to this page: mqueue.h(0p)time.h(0p)clock_getres(3p)mq_getattr(3p)mq_notify(3p)mq_open(3p)mq_receive(3p)mq_setattr(3p)mq_timedsend(3p)msgctl(3p)msgget(3p)msgrcv(3p)msgsnd(3p)