message queue problem

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mq_receive

mq_receive(3)						     Library Functions Manual						     mq_receive(3)

NAME

       mq_receive - Receives the oldest, highest-priority message from the message queue (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <mqueue.h>

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

PARAMETERS

       mqdes	   Specifies a message queue by descriptor.

       *msg_ptr    Specifies a pointer to a buffer to receive the message.

       msg_len	   Specifies the size of the receive buffer identified by the msg_ptr argument.

       *msg_prio   Specifies a pointer to a location to receive the message priority.

DESCRIPTION

       The  mq_receive	function  receives  the oldest, highest-priority message from the message queue. The message is removed from the queue and
       transferred to the buffer pointed to by the msg_ptr argument.

       If the specified message queue is empty and the O_NONBLOCK flag is not set with the mqdes argument, the mq_receive function blocks until  a
       message	is put on the queue or until the mq_receive function is interrupted by a signal.  If more than one process is waiting to receive a
       message when a message arrives at an empty queue, the highest-priority process that has been waiting the longest is selected to receive the
       message.  If the message queue is empty and the O_NONBLOCK flag is set, no message is removed from the queue, and an error is returned.

RETURN VALUES

       On successful completion, the function returns the length of the selected message.

       Otherwise, the function returns the value -1 and sets errno to indicate the error.  No message is removed from the queue.

ERRORS

       The mq_receive function fails under the following conditions:

       [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.

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

       [EFAULT]       An internal virtual memory error occurred.

       [EINTR]	      The mq_receive function was interrupted by a signal.

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

RELATED INFORMATION

       Functions: mq_send(3)

       Guide to Realtime Programming delim off

																     mq_receive(3)

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