mq_receive(3p) — Linux manual page

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.1‐2017, 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_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)