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<!-- $Id$ -->
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Author" CONTENT="James CE Johnson">
<TITLE>ACE Tutorial 011</TITLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
<CENTER><B><FONT SIZE=+2>ACE Tutorial 011</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Passing non-trivial data through an ACE_Message_Queue</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
Our Task object <A HREF="task.h">declaration</a> and <A HREF="task.cpp">definition</a>.
As with message_queue.cpp,
I've only commented the changes.
<P>
<HR WIDTH="100%">
<HR width=50%><P><center>task.h</center><HR width=50%>
<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> "<A HREF="../../../ace/Task.h">ace/Task.h</A>"
<font color=blue>#if !defined</font> (<font color=purple>ACE_LACKS_PRAGMA_ONCE</font>)
<font color=blue># pragma</font> <font color=purple>once</font>
<font color=blue>#endif</font> <font color=red>/* ACE_LACKS_PRAGMA_ONCE */</font>
class Task : public ACE_Task <ACE_MT_SYNCH>
{
public:
typedef ACE_Task <ACE_MT_SYNCH> inherited;
Task (size_t n_threads);
~Task (void);
int open (void * = 0);
int svc (void);
int close (u_long flags = 0);
protected:
ACE_Barrier barrier_;
size_t n_threads_;
};
<font color=blue>#endif</font> <font color=red>/* TASK_H */</font>
</PRE>
<HR width=50%><P><center>task.cpp</center><HR width=50%>
<PRE>
<font color=red>// $Id$</font>
<font color=blue>#include</font> "<font color=green>task.h</font>"
<font color=blue>#include</font> "<font color=green>block.h</font>"
<font color=blue>#include</font> "<font color=green>data.h</font>"
<font color=#008888>Task::Task</font> (size_t n_threads)
: barrier_ (n_threads),
n_threads_ (n_threads)
{
ACE_DEBUG ((LM_DEBUG,
"<font color=green>(%P|%t) Task ctor 0x%x\n</font>",
(void *) this));
}
<font color=#008888>Task::~Task</font> (void)
{
ACE_DEBUG ((LM_DEBUG,
"<font color=green>(%P|%t) Task dtor 0x%x\n</font>",
(void *) this));
ACE_Message_Block *message;
this->getq (message);
message->release ();
}
int
<font color=#008888>Task::open</font> (void *)
{
return this->activate (THR_NEW_LWP,
this->n_threads_);
}
int
<font color=#008888>Task::close</font> (u_long flags)
{
ACE_DEBUG ((LM_DEBUG,
"<font color=green>(%P|%t) Task close 0x%x\n</font>",
(void *) this));
return <font color=#008888>inherited::close</font> (flags);
}
int
<font color=#008888>Task::svc</font> (void)
{
this->barrier_.wait ();
ACE_DEBUG ((LM_DEBUG,
"<font color=green>(%P|%t) Task 0x%x starts in thread %d\n</font>",
(void *) this,
<font color=#008888>ACE_Thread::self</font> ()));
ACE_Message_Block *message;
for (;;)
{
if (this->getq (message) == -1)
ACE_ERROR_RETURN ((LM_ERROR,
"<font color=green>%p\n</font>",
"<font color=green>getq</font>"),
-1);
if (message->msg_type () == <font color=#008888>ACE_Message_Block::MB_HANGUP</font>)
{
this->putq (message);
break;
}
const char *cp = message->rd_ptr ();
<font color=red>// Don't forget to skip the NULL we inserted</font>
message->rd_ptr (<font color=#008888>ACE_OS::strlen</font> (cp) + 1);
ACE_DEBUG ((LM_DEBUG,
"<font color=green>(%P|%t) Block 0x%x contains (%s)\n</font>",
(void *) message,
cp));
<font color=red>/* Create a Data object into which we can extract the message
block contents. */</font>
Data data;
<font color=red>/* Use the rd_ptr() to access the message block data. Note that
we've already moved it past the text string in the block. */</font>
<font color=#008888>ACE_OS::memmove</font> ((char *) &data,
message->rd_ptr (),
sizeof (data));
message->rd_ptr (sizeof (data)); <font color=red>// Move the rd_ptr() beyond the data.</font>
<font color=red>/* Invoke a couple of method calls on the object we constructed. */</font>
data.who_am_i ();
data.what_am_i ();
<font color=red>/* An alternate approach:
Data * data;
data = (Data *)message->rd_ptr();
data->who_am_i();
data->what_am_i();
message->rd_ptr(sizeof(Data));
Even though this cuts down on the number of copies &
constructions, I'm not real fond of it. You can get into
trouble in a hurry by treating memory blocks as multiple data
types... */</font>
<font color=#008888>ACE_OS::sleep</font> (ACE_Time_Value (0, 5000));
message->release ();
}
return 0;
}
</PRE>
<HR WIDTH="100%">
<P>
Notice how we had to create a temporary Data object to copy the stuff out
of the message block? Again, if there were non-trivial ctor/dtors involved
then this wouldn't work at all.
<P>
Again, like <A HREF="../010/page01.html">Tutorial 10</A> we've skipped
<i>THR_DETACHED</i> because we <i>wait()</i> for the threads to exit
elsewhere.
<P><HR WIDTH="100%">
<CENTER>[<A HREF="../online-tutorials.html">Tutorial Index</A>] [<A HREF="page04.html">Continue This Tutorial</A>]</CENTER>
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