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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 002</TITLE>
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<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
<CENTER><B><FONT SIZE=+2>ACE Tutorial 002</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Creating a Better Server</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
<P>Like Tutorial 1, this is also a rather small program. I'm going
to add a couple of new ideas along the way but to make up for it I'm also
going to simplify the acceptor a great deal.
<P>
Kirthika's Abstract:
<UL>
This is a server example made simpler due to the use of off-the-shelf
components and classes from ACE.
<P>
Here, the Logging_Acceptor is an ACE_Acceptor class which is associated
with the Logging_Handler and the ACE_SOCK_ACCEPTOR. This will now
accept connection requests from the clients on being opened with the
reactor instance passed to it.
<P>
We also implement a signal to capture CTRL-C [ which generates SIGINT ] using ACE_SigAction and
ACE_SignalHandler. This signal can now be used to stop the reactor
from handling events.
<P>
Then, the reactor is allowed to loop infintely until it is shut down
using a ^C, after which both the reactor as well as the acceptor are
destroyed.
<P>
The Logging_Handler derives from the ACE_Svc_Handler instead of the
Event_Handler since the Svc_Handler has inbuilt SOCK_Stream and
provides all the calls needed by the reactor. The Svc_Handler has the
ability to react to events and communicate to remote tasks using the
underlying data stream passed to it.
<P>
A timer is scheduled in the reactor which does nothing but simply
display how it could be used to provide periodic processing when
needed. The ACE_TimeValue is used to set the time period.
<P>
Also, optimisations have been made in the form of a separate function
for
destroying the objects used.
<P>
Thus a simpler server has now been built which successfully
demonstrates how simple a task, writing a server can become on using
the various ACE components judiciously.
</UL>
<P>We begin by looking at the <A HREF="server.cpp">main (server.cpp)</A> portion program:
<P>
<HR WIDTH="100%">
<PRE>
<font color=red>// $Id$</font>
<font color=red>/*
As before, we need a few ACE objects as well as our Logging_Handler declaration.
*/</font>
<font color=blue>#include</font> "<font color=green>ace/Acceptor.h</font>"
<font color=blue>#include</font> "<font color=green>ace/SOCK_Acceptor.h</font>"
<font color=blue>#include</font> "<font color=green>ace/Reactor.h</font>"
<font color=blue>#include</font> "<font color=green>handler.h</font>"
<font color=red>/*
We'll still use the global reactor pointer. There's a snappy way around this
that shows up in later server tutorials.
*/</font>
ACE_Reactor * g_reactor;
<font color=red>/*
This was hinted at in Tutorial 1. Remember the hand-coded acceptor that we
created there? This template does all of that and more and better. If you
find yourself creating code that doesn't feel like a part of your application,
there's a good chance that ACE has a template or framework component to do
it for you.
*/</font>
typedef ACE_Acceptor < Logging_Handler, ACE_SOCK_ACCEPTOR > Logging_Acceptor;
<font color=red>/*
One of the new things will be a signal handler so that we can exit the application
somewhat cleanly. The 'finished' flag is used instead of the previous infninite
loop and the 'handler' will set that flag in respose to SIGINT (CTRL-C).
*/</font>
static sig_atomic_t finished = 0;
extern "<font color=green>C</font>" void handler (int)
{
finished = 1;
}
static const u_short PORT = ACE_DEFAULT_SERVER_PORT;
int main (int, char **)
{
<font color=red>// Create the reactor we'll register our event handler derivatives with.</font>
g_reactor = new ACE_Reactor;
<font color=red>// Create the acceptor that will listen for client connetions</font>
Logging_Acceptor peer_acceptor;
<font color=red>/*
Notice how similar this is to the open() call in Tutorial 1. I read
ahead when I created that one so that it would come out this way...
*/</font>
if (peer_acceptor.open (ACE_INET_Addr (PORT), g_reactor) == -1)
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>%p\n</font>", "<font color=green>open</font>"), -1);
<font color=red>/*
Here's the easiest way to respond to signals in your application. Simply
construct an ACE_Sig_Action object with a "<font color=green>C</font>" function and the signal you
want to capture. As you might expect, there is also a way to register
signal handlers with a reactor but we take the easy-out here.
*/</font>
ACE_Sig_Action sa ((ACE_SignalHandler) handler, SIGINT);
ACE_DEBUG ((LM_DEBUG, "<font color=green>(%P|%t) starting up server logging daemon\n</font>"));
<font color=red>// Perform logging service until the signal handler receives SIGINT.</font>
while (!finished)
g_reactor->handle_events ();
<font color=red>// Close the acceptor so that no more clients will be taken in.</font>
peer_acceptor.close();
<font color=red>// Free up the memory allocated for the reactor.</font>
delete g_reactor;
ACE_DEBUG ((LM_DEBUG, "<font color=green>(%P|%t) shutting down server logging daemon\n</font>"));
return 0;
}
<font color=blue>#if defined</font> (<font color=purple>ACE_HAS_EXPLICIT_TEMPLATE_INSTANTIATION</font>)
template class ACE_Acceptor <Logging_Handler, ACE_SOCK_ACCEPTOR>;
template class ACE_Svc_Handler<ACE_SOCK_STREAM, ACE_NULL_SYNCH>;
<font color=blue>#elif defined</font> (<font color=purple>ACE_HAS_TEMPLATE_INSTANTIATION_PRAGMA</font>)
<font color=blue>#pragma</font> <font color=purple>instantiate</font> ACE_Acceptor <Logging_Handler, ACE_SOCK_ACCEPTOR>
<font color=blue>#pragma</font> <font color=purple>instantiate</font> ACE_Svc_Handler<ACE_SOCK_STREAM, ACE_NULL_SYNCH>
<font color=blue>#endif</font> <font color=red>/* ACE_HAS_EXPLICIT_TEMPLATE_INSTANTIATION */</font>
</PRE>
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