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List:       kde-windows
Subject:    [Kde-windows] dcopserver only accepts one coneection on win32
From:       Christian Ehrlicher <Ch.Ehrlicher () gmx ! de>
Date:       2005-12-08 20:41:48
Message-ID: 43989A8C.10701 () gmx ! de
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Hi,

we have a problem with dcopserver on win32 - it only accepts one
connection. After a lot of debugging (I think I understand dcopserver
now much better :-) ) I found out that there is a problem with
QSocketNotifier. It just sends too much events and dcopserver gets into
an endless loop in dcop/KDE-ICE/misc.c:259.

The problem is the behaviour of WSAAsyncSelect used in qtcore to get
notification that new data has arrived. I'll try to explain (or read
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsock/winsock/wsaasyncselect_2.asp)
the problem:

client sends data -> WSAAsyncSelect creates an event ->
DCOPServer::processData() -> server reads data -> server and client are
communicating without a need for a socketnotifier -> ready -> because
new data arrived, an new event is created -> processData() is called but
can't read anything from the socket -> endless loop

WSAAsyncSelect stops sending events until it is reenabled by calling the
specific function. This means that I don't get an event until I called
recv().

But since DCOPServer::processData() sends and reads data, new events a
created...
My current hack is to disable the event notifier inside
DCOPServer::processData() (see attached patch). I'm unsure if this is ok
because I currently don't know what happens when new data arrives after
I called recv() the last time but QSocketNotifier isn't enabled yet. If
I get a notification, it will work, but if not, the server get out of
sync/the client waits forever.

I wonder how this worked with qt3 because there also WSAAsyncSelect is
used (at least I use it for qt3/free because I found no solution how to
get it working with select())

Christian



["dcop2.patch" (text/x-diff)]

Index: dcopserver.cpp
===================================================================
--- dcopserver.cpp	(revision 486802)
+++ dcopserver.cpp	(working copy)
@@ -440,6 +440,7 @@
 	: QSocketNotifier( IceConnectionNumber( conn ),
 			   QSocketNotifier::Read, 0 )
 {
+    setEnabled(false);
     iceConn = conn;
     notifyRegister = 0;
     _signalConnectionList = 0;
@@ -1153,8 +1154,11 @@
 
 void DCOPServer::processData( int /*socket*/ )
 {
-    IceConn iceConn = static_cast<const DCOPConnection*>(sender())->iceConn;
+    DCOPConnection *s = static_cast<DCOPConnection*>( sender() );
+    IceConn iceConn =  s->iceConn;
+    s->setEnabled(false);
     IceProcessMessagesStatus status = IceProcessMessages( iceConn, 0, 0 );
+    s->setEnabled(true);
     if ( status == IceProcessMessagesIOError ) {
         deadConnections.removeAll(iceConn);
         if (deadConnections.isEmpty())
@@ -1191,6 +1195,7 @@
         deadConnections.removeAll(iceConn);
 	(void) IceCloseConnection (iceConn);
     }
+	clients.value( iceConn )->setEnabled(true);
 }
 
 void* DCOPServer::watchConnection( IceConn iceConn )

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