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    Command:

    mq_receive

    
         library "librt"
    
    
    

    SYNOPSIS

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

    DESCRIPTION

         The mq_receive() system call receives oldest of the highest priority mes-
         sage(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 system call will fail and
         return an error.  Otherwise, the selected message will be removed from
         the queue and copied to the buffer pointed to by the msg_ptr argument.
    
         If the argument msg_prio is not NULL, the priority of the selected mes-
         sage will be stored in the location referenced by msg_prio.  If the spec-
         ified message queue is empty and O_NONBLOCK is not set in the message
         queue description associated with mqdes, mq_receive() will block until a
         message is enqueued on the message queue or until mq_receive() is inter-
         rupted by a signal.  If more than one thread is waiting to receive a mes-
         sage 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 will 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 will be removed from
         the queue, and mq_receive() will return an error.
    
         The mq_timedreceive() system call will receive the oldest of the highest
         priority messages from the message queue specified by mqdes as described
         for the mq_receive() system call.  However, if O_NONBLOCK was not speci-
         fied when the message queue was opened via the mq_open() system call, and
         no message exists on the queue to satisfy the receive, the wait for such
         a message will be terminated when the specified timeout expires.  If
         O_NONBLOCK is set, this system call is equivalent to mq_receive().
    
         The timeout expires 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.
    
         The timeout is based on the CLOCK_REALTIME clock.
    
    
    

    RETURN VALUES

                            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
                            abs_timeout 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.
    
    
    

    SEE ALSO

         mq_open(2), mq_send(2), mq_timedsend(2)
    
    
    

    STANDARDS

         The mq_receive() and mq_timedreceive() system calls conform to .
    
    
    

    HISTORY

         Support for POSIX message queues first appeared in FreeBSD 7.0.
    
    
    

    COPYRIGHT

         Portions of this text are reprinted and reproduced in electronic form
         from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology
         -- Portable Operating System Interface (POSIX), The Open Group Base Spec-
         ifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electri-
         cal 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 ref-
         eree document.  The original Standard can be obtained online at
              http://www.opengroup.org/unix/online.html.
    
    
    

    BSD November 29, 2005 BSD

    
    
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