<!-- page13.html,v 1.16 2003/08/19 15:08:26 schmidt Exp --> <HTML> <HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <META NAME="Author" CONTENT="James CE Johnson"> <TITLE>ACE Tutorial 015</TITLE> </HEAD> <BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F"> <CENTER><B><FONT SIZE=+2>ACE Tutorial 015</FONT></B></CENTER> <CENTER><B><FONT SIZE=+2>Building a protocol stream</FONT></B></CENTER> <P> <HR WIDTH="100%"> 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. <HR> <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> <P><HR WIDTH="100%"> <CENTER>[<A HREF="../online-tutorials.html">Tutorial Index</A>] [<A HREF="page14.html">Continue This Tutorial</A>]</CENTER>