As stated in the comments below, the default action of the task at the stream tail is to treat any received data as an error. In our implementation it will often happen that data gets through to the tail. How, then, do we handle this without creating an error condition? Simple: Create a custom Task for use as the stream tail that doesn't consider it an error to receive data.

Read on...

// $Id$

// EndTask.h
//
// Tutorial regarding a way to use ACE_Stream.
//
// written by bob mcwhirter (bob@netwrench.com)
//
//

#ifndef ENDTASK_H
#define ENDTASK_H

#include "Task.h"

// When you setup a Stream and push your modules on,
// there are two additional modules that go unseen
// by the user.
//
// The Stream pushes on a Stream_Head in front of
// your first module, and a Stream_Tail behind your
// last module.
//
// If your put () a message to the Stream Tail, it
// assumes you did so in error. This simple EndTask
// class allows you to push a message to it and just// have it safely Go Away.
//
// All this Task does is release the Message_Block
// and return 0.  It's a suitable black-hole.

class EndTask : public Task
{
public:
  typedef Task inherited;

  EndTask (const char *nameOfTask): inherited (nameOfTask, 0)
  {
    // when we get open ()'d, it with 0 threads since there is actually
    // no processing to do.

    ACE_DEBUG ((LM_INFO,
                " (%P|%t) Line: %d, File: %s\n",
                __LINE__,
                __FILE__));
  }

  virtual int open (void *)
  {
    ACE_DEBUG ((LM_INFO,
                " (%P|%t) Line: %d, File: %s\n",
                __LINE__,
                __FILE__));
    return 0;
  }

  virtual int open (void)
  {
    ACE_DEBUG ((LM_INFO,
                " (%P|%t) Line: %d, File: %s\n",
                __LINE__,
                __FILE__));
    return 0;
  }

  virtual ~EndTask (void)
  {
  }

  virtual int put (ACE_Message_Block *message,
                   ACE_Time_Value *timeout)
  {
    ACE_DEBUG ((LM_INFO,
                " (%P|%t) Line: %d, File: %s\n",
                __LINE__,
                __FILE__));
    ACE_UNUSED_ARG (timeout);

    // we don't have anything to do, so release () the message.
    ACE_DEBUG ((LM_DEBUG,
                " (%P|%t) %s EndTask::put () -- releasing Message_Block\n",
                this->nameOfTask ()));
    message->release ();
    return 0;
  }

};

#endif /* ENDTASK_H */