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<META NAME="Author" CONTENT="James CE Johnson">
<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>Let's see what things we've had to add to <A HREF="client_acceptor.h">client_acceptor.h</A>.
<P>
<HR WIDTH="100%">
<BR><FONT FACE="Arial,Helvetica">// $Id: client_acceptor.h,v 1.1 1998/08/30
16:04:11 jcej Exp $</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#ifndef CLIENT_ACCEPTOR_H</FONT>
<BR><FONT FACE="Arial,Helvetica">#define CLIENT_ACCEPTOR_H</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> The ACE_Acceptor<> template
lives in the ace/Acceptor.h header file. You'll</FONT>
<BR><FONT FACE="Arial,Helvetica"> find a very consitent naming
convention between the ACE objects and the</FONT>
<BR><FONT FACE="Arial,Helvetica"> headers where they can be
found. In general, the ACE object ACE_Foobar will</FONT>
<BR><FONT FACE="Arial,Helvetica"> be found in ace/Foobar.h.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#include "ace/Acceptor.h"</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Since we want to work with
sockets, we'll need a SOCK_Acceptor to allow the</FONT>
<BR><FONT FACE="Arial,Helvetica"> clients to connect to us.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica">#include "ace/SOCK_Acceptor.h"</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> The Client_Handler object
we develop will be used to handle clients once</FONT>
<BR><FONT FACE="Arial,Helvetica"> they're connected.
The ACE_Acceptor<> template's first parameter requires</FONT>
<BR><FONT FACE="Arial,Helvetica"> such an object. In
some cases, you can get by with just a forward</FONT>
<BR><FONT FACE="Arial,Helvetica"> declaration on the class,
in others you have to have the whole thing.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica">#include "client_handler.h"</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Parameterize the ACE_Acceptor<>
such that it will listen for socket</FONT>
<BR><FONT FACE="Arial,Helvetica"> connection attempts and create
Client_Handler objects when they happen. In</FONT>
<BR><FONT FACE="Arial,Helvetica"> Tutorial 001, we wrote the
basic acceptor logic on our own before we</FONT>
<BR><FONT FACE="Arial,Helvetica"> realized that ACE_Acceptor<>
was available. You'll get spoiled using the</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE templates because they
take away a lot of the tedious details!</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica">typedef ACE_Acceptor < Client_Handler,
ACE_SOCK_ACCEPTOR > Client_Acceptor_Base;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#include "thread_pool.h"</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> This time we've added quite
a bit more to our acceptor. In addition to</FONT>
<BR><FONT FACE="Arial,Helvetica"> providing a choice of concurrency
strategies, we also maintain a Thread_Pool</FONT>
<BR><FONT FACE="Arial,Helvetica"> object in case that strategy
is chosen. The object still isn't very complex</FONT>
<BR><FONT FACE="Arial,Helvetica"> but it's come a long way
from the simple typedef we had in Tutorial 5.</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> Why keep the thread pool as
a member? If we go back to the inetd concept</FONT>
<BR><FONT FACE="Arial,Helvetica"> you'll recall that we need
several acceptors to make that work. We may have</FONT>
<BR><FONT FACE="Arial,Helvetica"> a situation in which our
different client types requre different resources.</FONT>
<BR><FONT FACE="Arial,Helvetica"> That is, we may need a large
thread pool for some client types and a smaller</FONT>
<BR><FONT FACE="Arial,Helvetica"> one for others. We
could share a pool but then the client types may have</FONT>
<BR><FONT FACE="Arial,Helvetica"> undesirable impact on one
another.</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> Just in case you do want to
share a single thread pool, there is a constructor</FONT>
<BR><FONT FACE="Arial,Helvetica"> below that will let you do
that.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica">class Client_Acceptor : public Client_Acceptor_Base</FONT>
<BR><FONT FACE="Arial,Helvetica">{</FONT>
<BR><FONT FACE="Arial,Helvetica">public:</FONT>
<BR><FONT FACE="Arial,Helvetica">
typedef Client_Acceptor_Base inherited;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
Now that we have more than two strategies, we need more than a boolean</FONT>
<BR><FONT FACE="Arial,Helvetica">
to tell us what we're using. A set of enums is a good choice because</FONT>
<BR><FONT FACE="Arial,Helvetica">
it allows us to use named values. Another option would be a set of</FONT>
<BR><FONT FACE="Arial,Helvetica">
static const integers.</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
enum concurrency_t</FONT>
<BR><FONT FACE="Arial,Helvetica">
{</FONT>
<BR><FONT FACE="Arial,Helvetica">
single_threaded_,</FONT>
<BR><FONT FACE="Arial,Helvetica">
thread_per_connection_,</FONT>
<BR><FONT FACE="Arial,Helvetica">
thread_pool_</FONT>
<BR><FONT FACE="Arial,Helvetica">
};</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
The default constructor allows the programmer to choose the concurrency</FONT>
<BR><FONT FACE="Arial,Helvetica">
strategy. Since we want to focus on thread-pool, that's what we'll
use</FONT>
<BR><FONT FACE="Arial,Helvetica">
if nothing is specified.</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
Client_Acceptor( int _concurrency = thread_pool_ );</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
Another option is to construct the object with an existing thread pool.</FONT>
<BR><FONT FACE="Arial,Helvetica">
The concurrency strategy is pretty obvious at that point.</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
Client_Acceptor( Thread_Pool & _thread_pool );</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
Our destructor will take care of shutting down the thread-pool</FONT>
<BR><FONT FACE="Arial,Helvetica">
if applicable.</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
~Client_Acceptor( void );</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
Open ourselves and register with the given reactor. The thread pool
size</FONT>
<BR><FONT FACE="Arial,Helvetica">
can be specified here if you want to use that concurrency strategy.</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
int open( const ACE_INET_Addr & _addr, ACE_Reactor * _reactor,</FONT>
<BR><FONT FACE="Arial,Helvetica">
int _pool_size = Thread_Pool::default_pool_size_ );</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
Close ourselves and our thread pool if applicable</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
int close(void);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
What is our concurrency strategy?</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
int concurrency(void)</FONT>
<BR><FONT FACE="Arial,Helvetica">
{ return this->concurrency_; }</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
Give back a pointer to our thread pool. Our Client_Handler objects</FONT>
<BR><FONT FACE="Arial,Helvetica">
will need this so that their handle_input() methods can put themselves</FONT>
<BR><FONT FACE="Arial,Helvetica">
into the pool. Another alternative would be a globally accessible</FONT>
<BR><FONT FACE="Arial,Helvetica">
thread pool. ACE_Singleton<> is a way to achieve that.</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
Thread_Pool * thread_pool(void)</FONT>
<BR><FONT FACE="Arial,Helvetica">
{ return & this->the_thread_pool_; }</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
/*</FONT>
<BR><FONT FACE="Arial,Helvetica">
Since we can be constructed with a Thread_Pool reference, there are times</FONT>
<BR><FONT FACE="Arial,Helvetica">
when we need to know if the thread pool we're using is ours or if we're</FONT>
<BR><FONT FACE="Arial,Helvetica">
just borrowing it from somebody else.</FONT>
<BR><FONT FACE="Arial,Helvetica">
*/</FONT>
<BR><FONT FACE="Arial,Helvetica">
int thread_pool_is_private(void)</FONT>
<BR><FONT FACE="Arial,Helvetica">
{ return &the_thread_pool_ == &private_thread_pool_; }</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">protected:</FONT>
<BR><FONT FACE="Arial,Helvetica">
int concurrency_;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
Thread_Pool private_thread_pool_;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">
Thread_Pool & the_thread_pool_;</FONT>
<BR><FONT FACE="Arial,Helvetica">};</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#endif // CLIENT_ACCEPTOR_H</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P>
<HR WIDTH="100%">
<P>Well, except for the new Thread_Pool member variable, most of the changes
are informational.
<P>
<HR WIDTH="100%">
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