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<META NAME="Description" CONTENT="A first step towards using ACE productively">
<TITLE>ACE Tutorial 007</TITLE>
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<CENTER><B><FONT SIZE=+2>ACE Tutorial 007</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Creating a thread-pool server</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
<P>As you might expect, <A HREF="client_handler.h">client_handler.h</A>
is next.
<P>
<HR WIDTH="100%">
<BR>
<BR><FONT FACE="Arial,Helvetica">// $Id: client_handler.h,v 1.1 1998/08/30
23:47:14 schmidt Exp $</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#ifndef CLIENT_HANDLER_H</FONT>
<BR><FONT FACE="Arial,Helvetica">#define CLIENT_HANDLER_H</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Our client handler must exist
somewhere in the ACE_Event_Handler object</FONT>
<BR><FONT FACE="Arial,Helvetica"> hierarchy. This is
a requirement of the ACE_Reactor because it maintains</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE_Event_Handler pointers
for each registered event handler. You could</FONT>
<BR><FONT FACE="Arial,Helvetica"> derive our Client_Handler
directly from ACE_Event_Handler but you still have</FONT>
<BR><FONT FACE="Arial,Helvetica"> to have an ACE_SOCK_Stream
for the actually connection. With a direct</FONT>
<BR><FONT FACE="Arial,Helvetica"> derivative of ACE_Event_Handler,
you'll have to contain and maintain an</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE_SOCK_Stream instance
yourself. With ACE_Svc_Handler (which is a</FONT>
<BR><FONT FACE="Arial,Helvetica"> derivative of ACE_Event_Handler)
some of those details are handled for you.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#include "ace/Svc_Handler.h"</FONT>
<BR><FONT FACE="Arial,Helvetica">#include "ace/SOCK_Stream.h"</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">class Client_Acceptor;</FONT>
<BR><FONT FACE="Arial,Helvetica">class Thread_Pool;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Another feature of ACE_Svc_Handler
is it's ability to present the ACE_Task<></FONT>
<BR><FONT FACE="Arial,Helvetica"> interface as well.
That's what the ACE_NULL_SYNCH parameter below is all</FONT>
<BR><FONT FACE="Arial,Helvetica"> about. That's beyond
our scope here but we'll come back to it in the next</FONT>
<BR><FONT FACE="Arial,Helvetica"> tutorial when we start looking
at concurrency options.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica">class Client_Handler : public ACE_Svc_Handler
< ACE_SOCK_STREAM, ACE_NULL_SYNCH ></FONT>
<BR><FONT FACE="Arial,Helvetica">{</FONT>
<BR><FONT FACE="Arial,Helvetica">public:</FONT>
<BR><FONT FACE="Arial,Helvetica"> typedef ACE_Svc_Handler < ACE_SOCK_STREAM,
ACE_NULL_SYNCH > inherited;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> // Constructor...</FONT>
<BR><FONT FACE="Arial,Helvetica"> Client_Handler (void);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> The destroy()
method is our preferred method of destruction. We could</FONT>
<BR><FONT FACE="Arial,Helvetica"> have overloaded
the delete operator but that is neither easy nor</FONT>
<BR><FONT FACE="Arial,Helvetica"> intuitive (at
least to me). Instead, we provide a new method of</FONT>
<BR><FONT FACE="Arial,Helvetica"> destruction and
we make our destructor protected so that only ourselves,</FONT>
<BR><FONT FACE="Arial,Helvetica"> our derivatives
and our friends can delete us. It's a nice</FONT>
<BR><FONT FACE="Arial,Helvetica"> compromise.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> void destroy (void);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Most ACE objects
have an open() method. That's how you make them ready</FONT>
<BR><FONT FACE="Arial,Helvetica"> to do work.
ACE_Event_Handler has a virtual open() method which allows us</FONT>
<BR><FONT FACE="Arial,Helvetica"> to create this
overrride. ACE_Acceptor<> will invoke this method after</FONT>
<BR><FONT FACE="Arial,Helvetica"> creating a new
Client_Handler when a client connects. Notice that the</FONT>
<BR><FONT FACE="Arial,Helvetica"> parameter to
open() is a void*. It just so happens that the pointer</FONT>
<BR><FONT FACE="Arial,Helvetica"> points to the
acceptor which created us. You would like for the parameter</FONT>
<BR><FONT FACE="Arial,Helvetica"> to be an ACE_Acceptor<>*
but since ACE_Event_Handler is generic, that</FONT>
<BR><FONT FACE="Arial,Helvetica"> would tie it
too closely to the ACE_Acceptor<> set of objects. In our</FONT>
<BR><FONT FACE="Arial,Helvetica"> definition of
open() you'll see how we get around that.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> int open (void *_acceptor);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> When an ACE_Task<>
object falls out of the svc() method, the framework</FONT>
<BR><FONT FACE="Arial,Helvetica"> will call the
close() method. That's where we want to cleanup ourselves</FONT>
<BR><FONT FACE="Arial,Helvetica"> if we're running
in either thread-per-connection or thread-pool mode.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> int close(u_long flags = 0);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> When there is
activity on a registered handler, the handle_input() method</FONT>
<BR><FONT FACE="Arial,Helvetica"> of the handler
will be invoked. If that method returns an error code (eg</FONT>
<BR><FONT FACE="Arial,Helvetica"> -- -1) then the
reactor will invoke handle_close() to allow the object to</FONT>
<BR><FONT FACE="Arial,Helvetica"> clean itself
up. Since an event handler can be registered for more than</FONT>
<BR><FONT FACE="Arial,Helvetica"> one type of callback,
the callback mask is provided to inform</FONT>
<BR><FONT FACE="Arial,Helvetica"> handle_close()
exactly which method failed. That way, you don't have to</FONT>
<BR><FONT FACE="Arial,Helvetica"> maintain state
information between your handle_* method calls. The _handle</FONT>
<BR><FONT FACE="Arial,Helvetica"> parameter is
explained below...</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> int handle_close (ACE_HANDLE _handle,
ACE_Reactor_Mask _mask);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> When we register
with the reactor, we're going to tell it that we want to</FONT>
<BR><FONT FACE="Arial,Helvetica"> be notified of
READ events. When the reactor sees that there is read</FONT>
<BR><FONT FACE="Arial,Helvetica"> activity for
us, our handle_input() will be invoked. The _handleg</FONT>
<BR><FONT FACE="Arial,Helvetica"> provided is the
handle (file descriptor in Unix) of the actual connection</FONT>
<BR><FONT FACE="Arial,Helvetica"> causing the activity.
Since we're derived from ACE_Svc_Handler<> and it</FONT>
<BR><FONT FACE="Arial,Helvetica"> maintains it's
own peer (ACE_SOCK_Stream) object, this is redundant for</FONT>
<BR><FONT FACE="Arial,Helvetica"> us. However,
if we had been derived directly from ACE_Event_Handler, we</FONT>
<BR><FONT FACE="Arial,Helvetica"> may have chosen
not to contain the peer. In that case, the _handleg</FONT>
<BR><FONT FACE="Arial,Helvetica"> would be important
to us for reading the client's data.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> int handle_input (ACE_HANDLE _handle);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">protected:</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> If the Client_Acceptor
which created us has chosen a thread-per-connection</FONT>
<BR><FONT FACE="Arial,Helvetica"> strategy then
our open() method will activate us into a dedicate thread.</FONT>
<BR><FONT FACE="Arial,Helvetica"> The svc() method
will then execute in that thread performing some of the</FONT>
<BR><FONT FACE="Arial,Helvetica"> functions we
used to leave up to the reactor.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> int svc(void);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> This has nothing
at all to do with ACE. I've added this here as a worker</FONT>
<BR><FONT FACE="Arial,Helvetica"> function which
I will call from handle_input(). That allows me to</FONT>
<BR><FONT FACE="Arial,Helvetica"> introduce concurrencly
in later tutorials with a no changes to the worker</FONT>
<BR><FONT FACE="Arial,Helvetica"> function.
You can think of process() as application-level code and</FONT>
<BR><FONT FACE="Arial,Helvetica"> everything elase
as application-framework code.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> int process (char *_rdbuf, int
_rdbuf_len);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> We don't really
do anything in our destructor but we've declared it to be</FONT>
<BR><FONT FACE="Arial,Helvetica"> protected to
prevent casual deletion of this object. As I said above, I</FONT>
<BR><FONT FACE="Arial,Helvetica"> really would
prefer that everyone goes through the destroy() method to get</FONT>
<BR><FONT FACE="Arial,Helvetica"> rid of us.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> ~Client_Handler (void);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> When we
get to the definition of Client_Handler we'll see that there are</FONT>
<BR><FONT FACE="Arial,Helvetica">
several places where we go back to the Client_Acceptor for information.</FONT>
<BR><FONT FACE="Arial,Helvetica">
It is generally a good idea to do that through an accesor rather than</FONT>
<BR><FONT FACE="Arial,Helvetica">
using the member variable directly.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> Client_Acceptor * client_acceptor(
void )</FONT>
<BR><FONT FACE="Arial,Helvetica">
{ return this->client_acceptor_; }</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> And since
you shouldn't access a member variable directly, neither should you</FONT>
<BR><FONT FACE="Arial,Helvetica">
set (mutate) it. Although it might seem silly to do it this way,
you'll thank</FONT>
<BR><FONT FACE="Arial,Helvetica">
yourself for it later.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> void client_acceptor( Client_Acceptor
* _client_acceptor )</FONT>
<BR><FONT FACE="Arial,Helvetica">
{ this->client_acceptor_ = _client_acceptor; }</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> The concurrency()
accessor tells us the current concurrency strategy. It actually</FONT>
<BR><FONT FACE="Arial,Helvetica">
queries the Client_Acceptor for it but by having the accessor in place,
we could</FONT>
<BR><FONT FACE="Arial,Helvetica">
change our implementation without affecting everything that needs to know.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> int concurrency(void);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Likewise
for access to the Thread_Pool that we belong to.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> Thread_Pool * thread_pool(void);</FONT>
<BR><FONT FACE="Arial,Helvetica"></FONT> <FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> Client_Acceptor * client_acceptor_;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> For some
reason I didn't create accessor/mutator methods for this. So much
for</FONT>
<BR><FONT FACE="Arial,Helvetica">
consistency....</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
This variable is used to remember the thread in which we were created:
the "creator"</FONT>
<BR><FONT FACE="Arial,Helvetica">
thread in other words. handle_input() needs to know if it is operating
in the</FONT>
<BR><FONT FACE="Arial,Helvetica">
main reactor thread (which is the one that created us) or if it is operating
in</FONT>
<BR><FONT FACE="Arial,Helvetica">
one of the thread pool threads. More on this when we get to handle_input().</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE_thread_t
creator_;</FONT>
<BR><FONT FACE="Arial,Helvetica">};</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#endif // CLIENT_HANDLER_H</FONT>
<P>
<HR WIDTH="100%">
<P>Still, we're just not seeing a lot of changes due to intruduction of
the thread pool. That's a good thing! You don't want to go turning
your application upside down just because you changed thread models.
<P>
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