priority_buffer.cpp

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// priority_buffer.cpp,v 4.14 2003/12/30 23:18:58 shuston Exp

// This short program prints the contents of stdin to stdout sorted by
// the length of each line via the use of an ASX Message_Queue.  It
// illustrates how priorities can be used for ACE Message_Queues.

#include "ace/OS_NS_stdio.h"
#include "ace/Malloc_Base.h"    // To get ACE_Allocator
#include "ace/Message_Queue.h"
#include "ace/Read_Buffer.h"
#include "ace/Thread_Manager.h"
#include "ace/Service_Config.h"

ACE_RCSID(Message_Queue, priority_buffer, "priority_buffer.cpp,v 4.14 2003/12/30 23:18:58 shuston Exp")

#if defined (ACE_HAS_THREADS)

// Global thread manager.
static ACE_Thread_Manager thr_mgr;

// Make the queue be capable of being *very* large.
static const long max_queue = LONG_MAX;

// The consumer dequeues a message from the ACE_Message_Queue, writes
// the message to the stderr stream, and deletes the message.  The
// producer sends a 0-sized message to inform the consumer to stop
// reading and exit.

static void *
consumer (ACE_Message_Queue<ACE_MT_SYNCH> *msg_queue)
{
  // Keep looping, reading a message out of the queue, until we
  // timeout or get a message with a length == 0, which signals us to
  // quit.

  for (;;)
    {
      ACE_Message_Block *mb;

      if (msg_queue->dequeue_head (mb) == -1)
        break;

      int length = mb->length ();

      if (length > 0)
        ACE_OS::puts (mb->rd_ptr ());

      // Free up the buffer memory and the Message_Block.
      ACE_Allocator::instance ()->free (mb->rd_ptr ());
      mb->release ();

      if (length == 0)
        break;
    }

  return 0;
}

// The producer reads data from the stdin stream, creates a message,
// and then queues the message in the message list, where it is
// removed by the consumer thread.  A 0-sized message is enqueued when
// there is no more data to read.  The consumer uses this as a flag to
// know when to exit.

static void *
producer (ACE_Message_Queue<ACE_MT_SYNCH> *msg_queue)
{
  ACE_Read_Buffer rb (ACE_STDIN);

  // Keep reading stdin, until we reach EOF. 

  for (;;)
    {
      // Allocate a new buffer.
      char *buffer = rb.read ('\n');

      ACE_Message_Block *mb;

      if (buffer == 0)
        {
          // Send a 0-sized shutdown message to the other thread and
          // exit.

	  ACE_NEW_RETURN (mb, ACE_Message_Block ((size_t) 0), 0);

          if (msg_queue->enqueue_tail (mb) == -1)
            ACE_ERROR ((LM_ERROR, "(%t) %p\n", "put_next"));
          break;
        }

      // Enqueue the message in priority order.
      else
        {
          // Allocate a new message, but have it "borrow" its memory
          // from the buffer.
	  ACE_NEW_RETURN (mb, ACE_Message_Block (rb.size (),
						 ACE_Message_Block::MB_DATA,
						 0,
						 buffer),
			  0);
          mb->msg_priority (rb.size ());
          mb->wr_ptr (rb.size ());

          ACE_DEBUG ((LM_DEBUG,
		      "enqueueing message of size %d\n", 
                      mb->msg_priority ()));

          // Enqueue in priority order.
          if (msg_queue->enqueue_prio (mb) == -1)
            ACE_ERROR ((LM_ERROR, "(%t) %p\n", "put_next"));
        }
    }

  // Now read all the items out in priority order (i.e., ordered by
  // the size of the lines!).
  consumer (msg_queue);

  return 0; 
}

// Spawn off one thread that copies stdin to stdout in order of the
// size of each line.

int 
main (int, char *[])
{
  // Message queue.
  ACE_Message_Queue<ACE_MT_SYNCH> msg_queue (max_queue);

  if (thr_mgr.spawn (ACE_THR_FUNC (producer), (void *) &msg_queue,
                         THR_NEW_LWP | THR_DETACHED) == -1)
    ACE_ERROR_RETURN ((LM_ERROR, "%p\n", "spawn"), 1);

  // Wait for producer and consumer threads to exit.
  thr_mgr.wait ();
  return 0;
}
#else
int 
main (int, char *[])
{
  ACE_ERROR ((LM_ERROR, "threads not supported on this platform\n"));
  return 0;
}
#endif /* ACE_HAS_THREADS */