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

MQ_RECEIVE(3P)            POSIX Programmer's Manual           MQ_RECEIVE(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_receive, mq_timedreceive — receive a message from a message queue
       (REALTIME)

SYNOPSIS         top

       #include <mqueue.h>

       ssize_t mq_receive(mqd_t mqdes, char *msg_ptr, size_t msg_len,
           unsigned *msg_prio);

       #include <mqueue.h>
       #include <time.h>

       ssize_t mq_timedreceive(mqd_t mqdes, char *restrict msg_ptr,
           size_t msg_len, unsigned *restrict msg_prio,
           const struct timespec *restrict abstime);

DESCRIPTION         top

       The mq_receive() function shall receive the oldest of the highest
       priority message(s) from the message queue specified by mqdes.  If
       the size of the buffer in bytes, specified by the msg_len argument,
       is less than the mq_msgsize attribute of the message queue, the
       function shall fail and return an error. Otherwise, the selected
       message shall be removed from the queue and copied to the buffer
       pointed to by the msg_ptr argument.

       If the value of msg_len is greater than {SSIZE_MAX}, the result is
       implementation-defined.

       If the argument msg_prio is not NULL, the priority of the selected
       message shall be stored in the location referenced by msg_prio.

       If the specified message queue is empty and O_NONBLOCK is not set in
       the message queue description associated with mqdes, mq_receive()
       shall block until a message is enqueued on the message queue or until
       mq_receive() is interrupted by a signal. If more than one thread is
       waiting to receive a message when a message arrives at an empty queue
       and the Priority Scheduling option is supported, then the thread of
       highest priority that has been waiting the longest shall be selected
       to receive the message. Otherwise, it is unspecified which waiting
       thread receives the message. If the specified message queue is empty
       and O_NONBLOCK is set in the message queue description associated
       with mqdes, no message shall be removed from the queue, and
       mq_receive() shall return an error.

       The mq_timedreceive() function shall receive the oldest of the
       highest priority messages from the message queue specified by mqdes
       as described for the mq_receive() function. However, if O_NONBLOCK
       was not specified when the message queue was opened via the mq_open()
       function, and no message exists on the queue to satisfy the receive,
       the wait for such a message shall be terminated when the specified
       timeout expires. If O_NONBLOCK is set, this function is equivalent to
       mq_receive().

       The timeout expires 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 a
       message can be removed from the message queue immediately. The
       validity of the abstime parameter need not be checked if a message
       can be removed from the message queue immediately.

RETURN VALUE         top

       Upon successful completion, the mq_receive() and mq_timedreceive()
       functions shall return the length of the selected message in bytes
       and the message shall be removed from the queue. Otherwise, no
       message shall be removed from the queue, the functions shall return a
       value of −1, and set errno to indicate the error.

ERRORS         top

       These functions shall fail if:

       EAGAIN O_NONBLOCK was set in the message description associated with
              mqdes, and the specified message queue is empty.

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

       EMSGSIZE
              The specified message buffer size, msg_len, is less than the
              message size attribute of the message queue.

       EINTR  The mq_receive() or mq_timedreceive() operation was
              interrupted by a signal.

       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.

       ETIMEDOUT
              The O_NONBLOCK flag was not set when the message queue was
              opened, but no message arrived on the queue before the
              specified timeout expired.

       These functions may fail if:

       EBADMSG
              The implementation has detected a data corruption problem with
              the message.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       mq_open(3p), mq_send(3p), msgctl(3p), msgget(3p), msgrcv(3p),
       msgsnd(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_RECEIVE(3P)

Pages that refer to this page: mqueue.h(0p)time.h(0p)clock_getres(3p)mq_notify(3p)mq_open(3p)mq_send(3p)mq_timedreceive(3p)msgctl(3p)msgget(3p)msgrcv(3p)msgsnd(3p)