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   <TITLE>ACE Tutorial 015</TITLE>
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<CENTER><B><FONT SIZE=+2>ACE Tutorial 015</FONT></B></CENTER>

<CENTER><B><FONT SIZE=+2>Building a protocol stream</FONT></B></CENTER>

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The Protocol_Task implementation takes care of the open(), close(),
put() and svc() methods so that derivatives can concentrate on the
send() and recv() methods.  After a while you find that most
ACE_Task<> derivatives look very similar in the four basic methods and
only need one or two additional to do any real work.
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<PRE>

<font color=red>// page13.html,v 1.16 2003/08/19 15:08:26 schmidt Exp</font>

<font color=blue>#include</font> "<font color=green>Protocol_Task.h</font>"
<font color=blue>#include</font> "<A HREF="../../../ace/ACE.h">ace/ACE.h</A>"

<font color=red>// Construct the object and remember the thread count.</font>
<font color=#008888>Protocol_Task::Protocol_Task</font>(void)
{
    ;
}

<font color=#008888>Protocol_Task::~Protocol_Task</font>(void)
{
    ;
}

int <font color=#008888>Protocol_Task::open</font>(void *arg)
{
  ACE_UNUSED_ARG(arg);

  return(0);
}

int <font color=#008888>Protocol_Task::close</font>(u_long flags)
{
    ACE_UNUSED_ARG(flags);
    return 0;
}

<font color=red>/* When a message is put() onto the task, it's time to process() some data.
*/</font>
int <font color=#008888>Protocol_Task::put</font>(ACE_Message_Block *message,ACE_Time_Value *timeout)
{
    return this->process(message,timeout);
}

<font color=red>/* Return an error since we don't want the task to ever be activated.
 */</font>
int <font color=#008888>Protocol_Task::svc</font>(void)
{
    return -1;
}

<font color=red>/* There's nothing really magic about process().  We just decide if
   we're moving data upstream or downstream and invoke the appropriate
   virtual function to handle it.
*/</font>
int <font color=#008888>Protocol_Task::process</font>(ACE_Message_Block * message, ACE_Time_Value *timeout)
{
    if( this->is_writer() )
    {
        return this->send(message,timeout);
    }

    return this->recv(message,timeout);
}

<font color=red>/* We must insist that derivatives provide a meaningful overload for
   these methods.  It's fairly common for ACE object methods to return
   an error when an overload is expected but the method cannot be
   safely made pure virtual.
 */</font>

int <font color=#008888>Protocol_Task::send</font>(ACE_Message_Block *message,
                        ACE_Time_Value *timeout)
{
    ACE_UNUSED_ARG(message);
    ACE_UNUSED_ARG(timeout);
    return -1;
}

int <font color=#008888>Protocol_Task::recv</font>(ACE_Message_Block * message,
                        ACE_Time_Value *timeout)
{
    ACE_UNUSED_ARG(message);
    ACE_UNUSED_ARG(timeout);
    return -1;
}
</PRE>
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