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mq_receive(3)
NAME
  mq_receive - Receives the oldest, highest-priority message from the message
  queue (P1003.1b)

SYNOPSIS
  #include <mqueue.h>

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

LIBRARY
  Realtime Library (librt.so, librt.a)

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 option 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 option 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.

SEE ALSO
  Functions: mq_send(3)

  Guide to Realtime Programming

Index for Section 3

Alphabetical listing for M

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