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<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Author" CONTENT="James CE Johnson">
<TITLE>ACE Tutorial 010</TITLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
<CENTER><B><FONT SIZE=+2>ACE Tutorial 010</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Passing chunks of data through an ACE_Message_Queue</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
Our <A HREF="task.h">Task</A> object executes in one or more threads
and reads from the message queue it contains.
<P>
<HR WIDTH="100%">
<PRE>
<font color=red>// $Id$</font>
<font color=blue>#ifndef</font> <font color=purple>TASK_H</font>
<font color=blue>#define</font> <font color=purple>TASK_H</font>
<font color=blue>#include</font> "<font color=green>ace/Task.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=red>/*
Like the thread-pool server tutorial, we'll derive from ACE_Task<>.
Our goal here is to show off the ACE_Message_Queue and the best way
to do that is to use one to pass data between threads. The easiest
way to create threads is with ACE_Task<>
*/</font>
class Task : public ACE_Task < ACE_MT_SYNCH >
{
public:
typedef ACE_Task < ACE_MT_SYNCH > inherited;
<font color=red>/*
The constructor/destructor are simple but take care of some
necessary housekeeping.
*/</font>
Task (void);
~Task (void);
<font color=red>/*
To make our Task<> derivative look more like other ACE objects
I've added an open() method. It will take care of activate()ing
the object.
*/</font>
int open (int threads = 1);
<font color=red>/*
Our worker method
*/</font>
int svc (void);
<font color=red>/*
All we'll do here is print a message to the user.
*/</font>
int close (u_long flags = 0);
protected:
<font color=red>/*
Just to be clever, I'll use an ACE_Barrier to cause the threads
to sync in svc() before doing any real work.
*/</font>
ACE_Barrier *barrier_;
};
<font color=blue>#endif</font>
</PRE>
<HR WIDTH="100%">
<P>
The only thing here that we didn't see in the thread-pool server is the
ACE_Barrier. The application logic really doesn't need it but it is a
handy way to synchronize the threads at the beginning of svc(). In testing
I found that if I didn't sync svc(), the first thread to get activated would
tend to get all of the messages before the other threads came alive.
<P><HR WIDTH="100%">
<CENTER>[<A HREF="../online-tutorials.html">Tutorial Index</A>] [<A HREF="page05.html">Continue This Tutorial</A>]</CENTER>
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