ACE Tutorial 005
On the road to a multithreaded server

Ok, so we've got a main() loop that sets up the acceptor and we've seen how easy it is to create the acceptor object. So far, we've hardly written any code at all. Well, that's just about to change...

First, we look at client_handler.h for the declaration of the Client_Handler object. Then we look at the definition where all of the real work of the application takes place.

    // $Id: page04.html,v 1.11 1999/04/03 21:56:24 jcej Exp $

    #ifndef CLIENT_HANDLER_H
    #define CLIENT_HANDLER_H

    /* Our client handler must exist somewhere in the ACE_Event_Handler
       object hierarchy.  This is a requirement of the ACE_Reactor because
       it maintains ACE_Event_Handler pointers for each registered event
       handler.  You could derive our Client_Handler directly from
       ACE_Event_Handler but you still have to have an ACE_SOCK_Stream for
       the actual connection.  With a direct derivative of
       ACE_Event_Handler, you'll have to contain and maintain an
       ACE_SOCK_Stream instance yourself.  With ACE_Svc_Handler (which is
       a derivative of ACE_Event_Handler) some of those details are
       handled for you.  */

    #include "ace/Svc_Handler.h"

    #if !defined (ACE_LACKS_PRAGMA_ONCE)
    # pragma once
    #endif /* ACE_LACKS_PRAGMA_ONCE */

    #include "ace/SOCK_Stream.h"

    /* Another feature of ACE_Svc_Handler is it's ability to present the
       ACE_Task<> interface as well.  That's what the ACE_NULL_SYNCH
       parameter below is all about.  That's beyond our scope here but
       we'll come back to it in the next tutorial when we start looking at
       concurrency options.  */
    class Client_Handler : public ACE_Svc_Handler <ACE_SOCK_STREAM, ACE_NULL_SYNCH>
    {
    public:
      // Constructor...
      Client_Handler (void);

      /* The destroy() method is our preferred method of destruction.  We
        could have overloaded the delete operator but that is neither easy
        nor intuitive (at least to me).  Instead, we provide a new method
        of destruction and we make our destructor protected so that only
        ourselves, our derivatives and our friends can delete us. It's a
        nice compromise.  */
      void destroy (void);

      /* Most ACE objects have an open() method.  That's how you make them
        ready to do work.  ACE_Event_Handler has a virtual open() method
        which allows us to create an override.  ACE_Acceptor<> will invoke
        this method after creating a new Client_Handler when a client
        connects. Notice that the parameter to open() is a void*.  It just
        so happens that the pointer points to the acceptor which created
        us.  You would like for the parameter to be an ACE_Acceptor<>* but
        since ACE_Event_Handler is generic, that would tie it too closely
        to the ACE_Acceptor<> set of objects.  In our definition of open()
        you'll see how we get around that.  */
      int open (void *acceptor);

      /* When there is activity on a registered handler, the
        handle_input() method of the handler will be invoked.  If that
        method returns an error code (eg -- -1) then the reactor will
        invoke handle_close() to allow the object to clean itself
        up. Since an event handler can be registered for more than one
        type of callback, the callback mask is provided to inform
        handle_close() exactly which method failed.  That way, you don't
        have to maintain state information between your handle_* method
        calls. The <handle> parameter is explained below...  As a
        side-effect, the reactor will also invoke remove_handler() for the
        object on the mask that caused the -1 return.  This means that we
        don't have to do that ourselves!  */
      int handle_close (ACE_HANDLE handle,
                        ACE_Reactor_Mask mask);

    protected:

      /* When we register with the reactor, we're going to tell it that we
        want to be notified of READ events.  When the reactor sees that
        there is read activity for us, our handle_input() will be
        invoked. The _handle provided is the handle (file descriptor in
        Unix) of the actual connection causing the activity.  Since we're
        derived from ACE_Svc_Handler<> and it maintains its own peer
        (ACE_SOCK_Stream) object, this is redundant for us.  However, if
        we had been derived directly from ACE_Event_Handler, we may have
        chosen not to contain the peer.  In that case, the <handle> would
        be important to us for reading the client's data.  */
      int handle_input (ACE_HANDLE handle);

      /* This has nothing at all to do with ACE.  I've added this here as
        a worker function which I will call from handle_input().  That
        allows me to introduce concurrency in later tutorials with no
        changes to the worker function.  You can think of process() as
        application-level code and everything else as
        application-framework code.  */
      int process (char *rdbuf, int rdbuf_len);

      /* We don't really do anything in our destructor but we've declared
        it to be protected to prevent casual deletion of this object.  As
        I said above, I really would prefer that everyone goes through the
        destroy() method to get rid of us.  */
      ~Client_Handler (void);
    };

    #endif /* CLIENT_HANDLER_H */

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