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<META NAME="Description" CONTENT="A first step towards using ACE productively">
<TITLE>ACE Tutorial 005</TITLE>
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<CENTER><B><FONT SIZE=+2>ACE Tutorial 005</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>On the road to a multithreaded server</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
<P>We begin with <I><A HREF="server.cpp">server.cpp</A></I>.
<P>
<HR WIDTH="100%">
<P><FONT FACE="Arial,Helvetica">// $Id: server.cpp,v 1.5 1998/08/29 21:57:32
jcej Exp $</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> We try to keep main() very
simple. One of the ways we do that is to push</FONT>
<BR><FONT FACE="Arial,Helvetica"> much of the complicated stuff
into worker objects. In this case, we only</FONT>
<BR><FONT FACE="Arial,Helvetica"> need to include the acceptor
header in our main source file. We let it</FONT>
<BR><FONT FACE="Arial,Helvetica"> worry about the "real work".</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">#include "client_acceptor.h"</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> As before, we create a simple
signal handler that will set our finished</FONT>
<BR><FONT FACE="Arial,Helvetica"> flag. There are, of
course, more elegant ways to handle program shutdown</FONT>
<BR><FONT FACE="Arial,Helvetica"> requests but that isn't really
our focus right now, so we'll just do the</FONT>
<BR><FONT FACE="Arial,Helvetica"> easiest thing.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">static sig_atomic_t finished = 0;</FONT>
<BR><FONT FACE="Arial,Helvetica">extern "C" void handler (int)</FONT>
<BR><FONT FACE="Arial,Helvetica">{</FONT>
<BR><FONT FACE="Arial,Helvetica"> finished = 1;</FONT>
<BR><FONT FACE="Arial,Helvetica">}</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> A server has to listen for
clients at a known TCP/IP port. The default ACE</FONT>
<BR><FONT FACE="Arial,Helvetica"> port is 10002 (at least on
my system) and that's good enough for what we</FONT>
<BR><FONT FACE="Arial,Helvetica"> want to do here. Obviously,
a more robust application would take a command</FONT>
<BR><FONT FACE="Arial,Helvetica"> line parameter or read from
a configuration file or do some other clever</FONT>
<BR><FONT FACE="Arial,Helvetica"> thing. Just like the
signal handler above, though, that's what we want to</FONT>
<BR><FONT FACE="Arial,Helvetica"> focus on, so we're taking
the easy way out.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">static const u_short PORT = ACE_DEFAULT_SERVER_PORT;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Finally, we get to main.
Some C++ compilers will complain loudly if your</FONT>
<BR><FONT FACE="Arial,Helvetica"> function signature doesn't
match the prototype. Even though we're not</FONT>
<BR><FONT FACE="Arial,Helvetica"> going to use the parameters,
we still have to specify them.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica">int main (int argc, char *argv[])</FONT>
<BR><FONT FACE="Arial,Helvetica">{</FONT>
<BR><FONT FACE="Arial,Helvetica">/*</FONT>
<BR><FONT FACE="Arial,Helvetica"> In our earlier servers, we
used a global pointer to get to the reactor. I've</FONT>
<BR><FONT FACE="Arial,Helvetica"> never really liked that idea,
so I've moved it into main() this time. When</FONT>
<BR><FONT FACE="Arial,Helvetica"> we get to the Client_Handler
object you'll see how we manage to get a</FONT>
<BR><FONT FACE="Arial,Helvetica"> pointer back to this reactor.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE_Reactor reactor;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> The acceptor
will take care of letting clients connect to us. It will</FONT>
<BR><FONT FACE="Arial,Helvetica"> also arrange
for a Client_Handler to be created for each new client.</FONT>
<BR><FONT FACE="Arial,Helvetica"> Since we're only
going to listen at one TCP/IP port, we only need one</FONT>
<BR><FONT FACE="Arial,Helvetica"> acceptor.
If we wanted, though, we could create several of these and</FONT>
<BR><FONT FACE="Arial,Helvetica"> listen at several
ports. (That's what we would do if we wanted to rewrite</FONT>
<BR><FONT FACE="Arial,Helvetica"> inetd for
instance.)</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> Client_Acceptor peer_acceptor;</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Create an ACE_INET_Addr
that represents our endpoint of a connection. We</FONT>
<BR><FONT FACE="Arial,Helvetica"> then open our
acceptor object with that Addr. Doing so tells the acceptor</FONT>
<BR><FONT FACE="Arial,Helvetica"> where to listen
for connections. Servers generally listen at "well known"</FONT>
<BR><FONT FACE="Arial,Helvetica"> addresses.
If not, there must be some mechanism by which the client is</FONT>
<BR><FONT FACE="Arial,Helvetica"> informed of the
server's address.</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> Note how ACE_ERROR_RETURN
is used if we fail to open the acceptor. This</FONT>
<BR><FONT FACE="Arial,Helvetica"> technique is
used over and over again in our tutorials.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> if (peer_acceptor.open (ACE_INET_Addr
(PORT), &reactor) == -1)</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE_ERROR_RETURN ((LM_ERROR,
"%p\n", "open"), -1);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Here, we know
that the open was successful. If it had failed, we would</FONT>
<BR><FONT FACE="Arial,Helvetica"> have exited above.
A nice side-effect of the open() is that we're already</FONT>
<BR><FONT FACE="Arial,Helvetica"> registered with
the reactor we provided it.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Install our signal
handler. You can actually register signal handlers</FONT>
<BR><FONT FACE="Arial,Helvetica"> with the reactor.
You might do that when the signal handler is</FONT>
<BR><FONT FACE="Arial,Helvetica"> responsible for
performing "real" work. Our simple flag-setter doesn't</FONT>
<BR><FONT FACE="Arial,Helvetica"> justify deriving
from ACE_Event_Handler and providing a callback function</FONT>
<BR><FONT FACE="Arial,Helvetica"> though.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE_Sig_Action sa ((ACE_SignalHandler)
handler, SIGINT);</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> Like ACE_ERROR_RETURN,
the ACE_DEBUG macro gets used quite a bit. It's a</FONT>
<BR><FONT FACE="Arial,Helvetica"> handy way to
generate uniform debug output from your program.</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> ACE_DEBUG ((LM_DEBUG, "(%P|%t)
starting up server daemon\n"));</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> /*</FONT>
<BR><FONT FACE="Arial,Helvetica"> This will loop
"forever" invoking the handle_events() method of our</FONT>
<BR><FONT FACE="Arial,Helvetica"> reactor. handle_events()
watches for activity on any registered handlers</FONT>
<BR><FONT FACE="Arial,Helvetica"> and invokes their
appropriate callbacks when necessary. Callback-driven</FONT>
<BR><FONT FACE="Arial,Helvetica"> programming is
a big thing in ACE, you should get used to it. If the</FONT>
<BR><FONT FACE="Arial,Helvetica"> signal handler
catches something, the finished flag will be set and we'll</FONT>
<BR><FONT FACE="Arial,Helvetica"> exit. Conveniently
enough, handle_events() is also interrupted by signals</FONT>
<BR><FONT FACE="Arial,Helvetica"> and will exit
back to the while() loop. (If you want your event loop to</FONT>
<BR><FONT FACE="Arial,Helvetica"> not be interrupted
by signals, checkout the <i>restart</i> flag on the</FONT>
<BR><FONT FACE="Arial,Helvetica"> open() method
of ACE_Reactor if you're interested.)</FONT>
<BR><FONT FACE="Arial,Helvetica"> */</FONT>
<BR><FONT FACE="Arial,Helvetica"> while (!finished)</FONT>
<BR><FONT FACE="Arial,Helvetica"> reactor.handle_events
();</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> ACE_DEBUG ((LM_DEBUG, "(%P|%t) shutting
down server daemon\n"));</FONT><FONT FACE="Arial,Helvetica"></FONT>
<P><FONT FACE="Arial,Helvetica"> return 0;</FONT>
<BR><FONT FACE="Arial,Helvetica">}</FONT>
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