ACE Tutorial 001
A Beginners Guide to Using the ACE Toolkit


Now we begin to look at the acceptor object.


#if !defined (_CLIENT_ACCEPTOR_H)
#define _CLIENT_ACCEPTOR_H

/*
  A SOCK_Acceptor knows how to accept socket connections.  We'll use
  one of those at the heart of our Logging_Acceptor.
 */
#include "ace/SOCK_Acceptor.h"

/*
  An Event_Handler is what you register with ACE_Reactor.  When events occur,
  the reactor will callback on the Event_Handler.  More on that in a few lines.
 */
#include "ace/Event_Handler.h"

/*
  When a client connects, we'll create a Logging_Handler to deal with the
  connection.  Here, we bring in that declaration.
 */
#include "logger.h"

/*
  Our Logging_Acceptor is derived from ACE_Event_Handler.  That lets the
  reactor treat our acceptor just like every other handler.
 */
class Logging_Acceptor : public ACE_Event_Handler
{

friend class Logging_Handler;

public:

  /*
    For this simple case we won't bother with either constructor or
    destructor.  In a real application you would certainly have them.
   */

  /*
    Here's the open() method we called from main().  We have two things
    to accomplish here:  (1)  Open the acceptor so that we can hear
    client requests and (2) register ourselves with the reactor so that
    we can respond to those requests.
   */
  int open (const ACE_INET_Addr &_addr, ACE_Reactor * _reactor )
  {
    /*
      Perform the open() on the acceptor.  We pass through the address
      at which main() wants us to listen.  The second parameter tells
      the acceptor it is OK to reuse the address.  This is necessary
      sometimes to get around closed connections that haven't timed out.
     */
     if (this->peer_acceptor_.open (_addr, 1) == -1)
       return -1;

    /*
      Remember the reactor we're using.  We'll need it later when we
      create a client connection handler.
     */
    reactor_ = _reactor;

    /*
      Now we can register with the reactor we were given.  Since the reactor
      pointer is global, we could have just used that but it's gross enough
      already.
      Notice that we can pass 'this' right into the registration since we're
      derived from ACE_Event_Handler.  We also provide ACCEPT_MASK to tell
      the reactor that we want to know about accept requests from clients.
     */
    return _reactor->register_handler( this, ACE_Event_Handler::ACCEPT_MASK );
  }
        
private:

  /*
    To provide multi-OS abstraction, ACE uses the concept of "handles" for
    connection endpoints.  In Unix, this is a traditional file descriptor
    (or integer).  On other OS's, it may be something else.
    The reactor will need to get the handle (file descriptor) to satisfy
    it's own internal needs.  Our relevant handle is the handle of the
    acceptor object, so that's what we provide.
   */
  ACE_HANDLE get_handle (void) const
  { 
    return this->peer_acceptor_.get_handle (); 
  }

  /*
    When an accept request arrives, the reactor will invoke the handle_input()
    callback.  This is where we deal with the connection request.
   */
  int handle_input (ACE_HANDLE)
  {
    /*
      In response to the connection request, we create a new Logging_Handler.
      This new object will be used to interact with the client until it
      disconnects.
     */
    Logging_Handler *svc_handler = new Logging_Handler;
        
    /*
      To complete the connection, we invoke the accept() method call on
      the acceptor object and provide it with the connection handler instance.
      This transfers "ownership" of the connection from the acceptor to the
      connection handler.
     */
    if (this->peer_acceptor_.accept (*svc_handler) == -1)
      ACE_ERROR_RETURN ((LM_ERROR, "%p", "accept failed"), -1);

    /*
      Again, most objects need to be open()ed before they are useful.  We'll
      give the handler our reactor pointer so that it can register for
      events as well.  If the open fails, we'll force a close().
     */
    if (svc_handler->open (reactor_) == -1)
      svc_handler->close ();
        
    return 0;
  }

protected:

  /*
    Our acceptor object instance
   */
  ACE_SOCK_Acceptor peer_acceptor_;     

  /*
    A place to remember our reactor pointer
   */
  ACE_Reactor * reactor_;
};

#endif /* _CLIENT_ACCEPTOR_H */



It is important to notice here that we have done very little application-specifc code in developing this object. In fact, if we take out the progress information, the only app-specific code is when we create the new Logging_Handler object to give to the accept function. You may begin to wonder why there isn't a C++ template that does all of this coding for you. Actually, the ACE toolkit happens to have one handy: We would have used it like this: This will create a piece of code similar to what I've shown above. The primary difference is that the handle_input function created by the template does NOT register the handler with the reactor. In the long-run, that is good for us because we can then move that logic into the open function of the Logging_Handler and use a completely-generic acceptor.

Now that we know how to accept a connection request, let's move on to the next page where we learn how to handle the actual connection. Even though we just learned about this cool template thing, we will continue to use the "hand-written" acceptor developed above. As I mentioned, the only difference will be in the open function of the connection handler anyway.


[Tutorial Index] [Previous Page] [Continue This Tutorial]