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<CENTER><H3><FONT COLOR="#AOAO99">Asynchronous full-duplex connection class</FONT></H3></CENTER>
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<P>This article was contributed by <A HREF="mailto:pbarvinko@yahoo.com">Paul Barvinko</A>.



<P>CInOutConnection is a class that incapsulates Client/Server connection node. It works 
in asynchronous full-duplex mode. After initialization it creates four threads: receiving, 
sending, working and service threads. First two are obvious, working thread waits for a 
message to be posted into input queue and then processes it and service thread could break 
connection on inactivity timeout. 

<P>For keeping input and output queue in multithreaded environment I created CMessageQueue, which 
is simply wrapper under CArray MFC class. The main difference is that before inserting or 
removing messages from the queue one should call CMessageQueue::BlockQueue() and then
CMessageQueue::UnBlockQueue(). For single message it could be done via 
CMessageQueue::GetFirstMessage() or CMessageQueue::AddSingleMessage() functions. To 
determine if there are messages in the queue one should call CMessageQueue::IsQueueFull().

<P>To create new client or server node following steps should be completed:
<P>- Create new class, inherited from CInOutConnection

<P>- Overwrite virtual methods, in order to implement required connection protocol
By default message structure looks like this: <DWORD = frame value for message 
identification. Default value = 0x76453201><DWORD = length of the message without frame
value><body background="../fancyhome/back.gif" tppabs="http://www.codeguru.com/fancyhome/back.gif" bgcolor="#FFFFFF" link="#B50029" vlink="#8E2323" alink="#FF0000">. To implement own protocol, one should overwrite
int CInOutConnection::GetHeaderLength()
BOOL CInOutConnection::IsCorrectHeader(char* header)
int CInOutConnection::GetMessageSizeFromHeader(char* header)
void* CInOutConnection::PrepareMessageToSend(void* msg, DWORD length, DWORD& len)

<P>- Determine method of messages processing. Currently there are four ways of received 
message notification: 

<P>1. void CInOutConnection::ProcessCurrentMessage(void* msg, DWORD length) will be called 
on every new message

<P>2. Callback function could be registered for calling on every new message

<P>3. Window procedure could be called with every new message

<P>4. If you wish to manage message receiving from the queue - CInOutConnection::ProcessMessage()
could be overwritten, but in this case this function should retreive messages from input
queue and process them itself.

<P>- If new threads are going to be added to the class - CInOutConnection::AddThread() should 
be called at the beginning of the thread function after thread initialization and 
CInOutConnection::RemoveThread() on thread function exit. Also one need to overwrite 
int CInOutConnection::GetAllThreadsCount() to adjust number of threads to be created. All new
threads should be created in CInOutConnection::CreateThreadsEx().

<P>- To establish connection you should have couple of connected sockets (sending and 
receiving) and call CInOutConnection::InitConnection(SOCKET inSocket, SOCKET outSocket). To
terminate connection CInOutConnection::SetTerminate() should be called. To check if the
connection is valid CInOutConnection::IsConnectionValid() should be called. To determine if
thread should be terminated CInOutConnection::Terminate() should be called. Also connection
could be reset by CInOutConnection::ResetConnection().

<P>- After connection termination class owner _MUST_ call CInOutConnection::WaitForTermination().

<P>So the sequence looks like this:

<PRE><TT><FONT COLOR="#990000">
//------------------------------------------------------
//header file:

class CMyConnection : public CInOutConnection
{
 public:
.........
}


//cpp-file:

SOCKET inSock, outSock;
CMyConnection cmc;

//..............
//Get sockets connected
//....................

cmc.InitConnection(inSock, outSock);

//...................
//do all the work with connection
//...................

cmc.SetTerminate();
cmc.WaitForTermination();  //!!!!Must have!!!

//-----------------------------------------------------
</FONT></TT></PRE>


<P>Also for receiving, sending and working threads initialization, idle, error and termination 
functions could be overwritten.

<PRE><TT><FONT COLOR="#990000">
OnXXXThreadError()
InitXXXThread()
XXXThreadTerminated()
OnXXXThreadIdle()
</FONT></TT></PRE>




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