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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>
<HR WIDTH="100%">
<P>
We'll look first at <A HREF="message_queue.cpp">main()</A>.
<P>
<HR WIDTH="100%">
<PRE>
/*
To illustrate the ACE_Message_Queue, we use a derivative of ACE_Task<>. We
also derive from ACE_Message_Block to show that we don't have memory leaks.
*/
#include "task.h"
#include "block.h"
int run_test( int iterations, int threads )
{
/*
Create and open an instance of our Task object. I've overridden the
open() method to make it look more like other ACE objects.
*/
Task task;
if (task.open (threads) == -1)
{
ACE_ERROR_RETURN ((LM_ERROR, "%p\n", "open"), -1);
}
/*
Give the threads a moment to open. This isn't really necessary but if we
don't we find that all of our blocks are constructed and enqueued before
any of the threads get created. Basically, the sleep() makes the output
look more interesting.
*/
ACE_OS::sleep (ACE_Time_Value (1));
int i;
for (i = 0; i < iterations; ++i)
{
/*
Create a new message block to hold our data. Here, we ask for a block
that has 128 bytes of data space.
*/
Block *message = new Block (128);
/*
Grab the "write pointer". This is a pointer into the data area where we
can write our data. After writting the data you have to increment the
wr_ptr() so that subsequent writes won't clobber what you've put there.
*/
ACE_OS::sprintf (message->wr_ptr (), "This is message %d.", i);
message->wr_ptr (strlen (message->rd_ptr ()));
/*
Put the message block into the queue. One of the threads in the Task
object will pick up the block and "do work" on it.
*/
if (task.putq (message) == -1)
{
break;
}
}
/*
Once we're done, we have to signal the Task objects to shut down. There
are several choices including: - Send a message of zero length - Send a
message with a special content I don't like these choices because they're
likely to interfere with application logic. Instead, I use the message
type feature to send a message of type "hangup". The default type is
MB_DATA, so when the tasks get a MB_HANGUP type, they know to go away.
*/
Block *message = new Block ();
message->msg_type (ACE_Message_Block::MB_HANGUP);
task.putq (message);
/*
Wait for the threads in our task object to go away.
*/
task.wait ();
return(0);
}
int main (int argc, char *argv[])
{
/*
Set the number of iterations through our putq() loop and the number of
threads to use in our Task<> derivative.
*/
int iterations = argc > 1 ? atoi (argv[1]) : 9;
int threads = argc > 2 ? atoi (argv[2]) : 2;
(void)run_test(iterations,threads);
ACE_DEBUG ((LM_DEBUG, "(%P|%t) Application exiting\n"));
exit(0);
}
</PRE>
<HR WIDTH="100%">
<P>
This looks a lot like our thread-pool server and it even does some things
better. In particular, I've scoped the Task object so that it's destructor
will have a chance to get called before the application exits.
Notice how we write actual data into the message block though. In the thread-pool
server we just provided a pointer. Writting the data is actually a more correct
way of doing things since you don't get into strange pointer casting situations.
What if you want to put complex objects into the message block though? We'll do
that in the next tutorial, let's stick with the basics first.
<P>
On the next page we'll take a look at our Block object...
<P>
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