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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<TITLE>ACE Tutorial 001</TITLE>
<META NAME="GENERATOR" CONTENT="Mozilla/3.01Gold (Win95; I) [Netscape]">
<META NAME="Author" CONTENT="James CE Johnson">
<META NAME="Description" CONTENT="A first step towards using ACE productively">
</HEAD>
<BODY text = "#000000" link="#000fff" vlink="#ff0f0f" bgcolor="#ffffff">
<CENTER><P><B><FONT SIZE=+2>ACE Tutorial 001<BR>
A Beginners Guide to Using the ACE Toolkit</FONT></B></P></CENTER>
<hr>
<P>Now we begin to look at the <A HREF="logger.h">logger</A>
object.
<P>
<HR>
<PRE>
<font color=red>// $Id$</font>
<font color=blue>#ifndef</font> <font color=purple>_CLIENT_HANDLER_H</font>
<font color=blue>#define</font> <font color=purple>_CLIENT_HANDLER_H</font>
<font color=red>/*
A connection handler will also be derived from ACE_Event_Handler so that we
can register with a reactor.
*/</font>
<font color=blue>#include</font> "<font color=green>ace/Event_Handler.h</font>"
<font color=blue>#if !defined</font> (<font color=purple>ACE_LACKS_PRAGMA_ONCE</font>)
# pragma once
<font color=blue>#endif</font> <font color=red>/* ACE_LACKS_PRAGMA_ONCE */</font>
<font color=blue>#include</font> "<font color=green>ace/INET_Addr.h</font>"
<font color=red>/*
Since we're doing TCP/IP, we'll need a SOCK_Stream for the connection.
*/</font>
<font color=blue>#include</font> "<font color=green>ace/SOCK_Stream.h</font>"
class Logging_Handler : public ACE_Event_Handler
{
public:
<font color=red>/*
Like the acceptor, we're simple enough to avoid constructor and destructor.
*/</font>
<font color=red>/*
To open the client handler, we have to register ourselves with the reactor.
Notice that we don't have to "<font color=green>open</font>" our ACE_SOCK_Stream member variable.
Why? Because the call to the acceptor's accept() method took care of those
details for us.
*/</font>
int open ( ACE_Reactor * _reactor )
{
<font color=red>/*
Remember our reactor...
*/</font>
reactor_ = _reactor;
<font color=red>/*
In this case we're using the READ_MASK. Like the acceptor, handle_input()
will be called due to this mask but it's a nice piece of bookkeeping to
have separate masks for the separate types of activity.
*/</font>
if (_reactor-> register_handler (this, <font color=#008888>ACE_Event_Handler::READ_MASK</font>) == -1)
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>(%P|%t) can't register with reactor\n</font>"), -1);
return 0;
}
<font color=red>/*
If we're explicitly closed we'll close our "<font color=green>file handle</font>". The net result
is to close the connection to the client and remove ourselves from the
reactor if we're registered
*/</font>
int close (void)
{
return this->handle_close (ACE_INVALID_HANDLE, <font color=#008888>ACE_Event_Handler::RWE_MASK</font>);
}
<font color=red>/*
This is a bit of magic... When we call the accept() method of the acceptor
object, it wants to do work on an ACE_SOCK_Stream. We have one of those as
our connection to the client but it would be gross to provide a method to
access that object. It's much cooler if the acceptor can just treat the
Logging_Handler as an ACE_SOCK_Stream. Providing this cast operator lets
that happen cleanly.
*/</font>
operator ACE_SOCK_Stream &()
{
return this->cli_stream_;
}
protected:
<font color=red>/*
Again, like the acceptor, we need to provide the connection handle to the reactor.
*/</font>
ACE_HANDLE get_handle (void) const
{
return this->cli_stream_.get_handle ();
}
<font color=red>/*
And here's the handle_input(). This is really the workhorse of the application.
*/</font>
virtual int handle_input (ACE_HANDLE)
{
<font color=red>/*
Create and initialize a small receive buffer.
*/</font>
char buf[128];
memset(buf,0,sizeof(buf));
<font color=red>/*
Invoke the recv() method of the ACE_SOCK_Stream to get some data. It will
return -1 if there is an error. Otherwise, it will return the number of bytes
read. Of course, if it read zero bytes then the connection must be gone.
How do I know that? Because handle_input() would not be called by the reactor
if there wasn't *some* kind of activity and a closed connection looks like a
read request to the reactor. But when you read from a closed connection you'll
read zero bytes.
Notice that in the error case or closed case we return -1. That tells the reactor
to call our handle_close() where we'll take care of shutting down cleanly.
Although we don't make use of them, there are additional parameters you can
use with the recv() call. One of these is an ACE_Time_Value that allows you to
limit the amount of time blocking on the recv(). You would use that if you
weren't sure if data was available. Since we only get to handle_input() when
data is ready, that would be redundant. On the other hand, if you use recv_n()
to read *exactly* a number of bytes then limiting the time you wait for those
bytes might be good.
The other paramter that may come in handy is an integer <i>flags</i>. This is
passed directly to the underlying OS recv() call. See the man page recv(2)
and the header sys/socket.h for the gory details.
*/</font>
switch( this->cli_stream_.recv(buf,sizeof buf) )
{
case -1:
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>(%P|%t) %p bad read\n</font>", "<font color=green>client logger</font>"), -1);
case 0:
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>(%P|%t) closing log daemon (fd = %d)\n</font>",
this->get_handle ()), -1);
default:
ACE_DEBUG ((LM_DEBUG, "<font color=green>(%P|%t) from client: %s</font>",buf));
}
return 0;
}
<font color=red>/*
When handle_input() returns -1, we'll end up here. There are a few housekeeping
chores to handle.
*/</font>
int handle_close (ACE_HANDLE, ACE_Reactor_Mask _mask)
{
<font color=red>/*
Remove ourselves from the reactor. We have to include the DONT_CALL in the
mask so that it won't call handle_close() on us again!
*/</font>
reactor_->remove_handler(this,_mask|<font color=#008888>ACE_Event_Handler::DONT_CALL</font>);
<font color=red>/*
Close the socket that we're connected to the client with.
*/</font>
cli_stream_.close();
<font color=red>/*
Since we know we were dynamically allocated by the acceptor, now is a good
time to get rid of ourselves.
*/</font>
delete this;
return 0;
}
protected:
<font color=red>/*
Our peer connection.
*/</font>
ACE_SOCK_Stream cli_stream_;
<font color=red>/*
Our reactor (and our acceptor's reactor).
*/</font>
ACE_Reactor * reactor_;
};
<font color=blue>#endif</font> <font color=red>/* _CLIENT_HANDLER_H */</font>
</PRE>
<HR WIDTH="100%">
<P>
The comments really should tell the story. The really
interesting stuff is in <i>handle_input()</i>. Everything
else is just housekeeping.
In the future, we'll learn about ACE_Svc_Handler<>
which will take care of most of the housekeeping for us.
<P>
<P><HR WIDTH="100%">
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