RE: [Quickfix-developers] Fixed spurious System.NullReferenceException in .NET Application.toApp()
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RE: [Quickfix-developers] Fixed spurious System.NullReferenceException in .NET Application.toApp()
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From: James C. D. <jc...@co...> - 2004-10-19 18:36:15
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Vladimir, I concur with Oren. Great job and thanks for releasing this back to QuickFIX. Also, your explanation of the problem is a nice reminder for anyone mixing managed and unmanaged code. Thanks again, Jim James C. Downs Connamara Systems, LLC 53 W. Jackson Blvd Suite 1627 Chicago, IL 60604 312 - 282 - 7746 www.connamara.com -----Original Message----- From: qui...@li... [mailto:qui...@li...] On Behalf Of Vladimir Arnost Sent: Tuesday, October 19, 2004 12:03 PM To: qui...@li... Cc: Vladimir Sebesta Subject: [Quickfix-developers] Fixed spurious System.NullReferenceException in .NET Application.toApp() QuickFIX Documentation: http://www.quickfixengine.org/quickfix/doc/html/index.html QuickFIX FAQ: http://www.quickfixengine.org/wikifix/index.php?QuickFixFAQ QuickFIX Support: http://www.quickfixengine.org/services.html Oren, I have fixed a nasty bug in .NET Application class in QuickFIX 1.9.2. From time to time, especially under high system load, sending a FIX message throws an exception like this one: System.NullReferenceException: Object reference not set to an instance of an object. at FIX.message_order.=(message_order* , message_order* ) at FIX.message_order.__ctor(message_order* , message_order* copy) at std._Tree<std::_Tmap_traits<int,FIX::FieldBase,FIX::message_order,...> >.key_comp(_Tree<...>* , message_order* ) at FIX.FieldMap.=(FieldMap* , FieldMap* ) at FIX.Message.=(Message* , Message* ) at Application.toApp(Application* , Message* message, SessionID* sessionID) at FIX.Session.sendToTarget(Message* , SessionID* ) at QuickFix.Session.sendToTarget(Message message, SessionID sessionID) (The exception was thrown at random code locations, but always "below" FIX.FieldMap.operator=) As I have found, the problem lies in mixing unmanaged code and garbage-collected data structures. Method toApp() creates managed wrapper class QuickFix::Message for unmanaged class FIX::Message, calls managed method toApp() and copies the (modified?) message back to FIX::Message. The problem is in the last operation, which will fail if the .NET garbage collector decides to move QuickFix::Message in memory while the unmanaged assignment operator is obliviously copying toMessage->unmanaged() back to message. This happens quite rarely (once in 10000 messages or so), but the message is lost and never sent to the client (sequence gap does not occur), which makes the problem very severe. void toApp( FIX::Message& message, const FIX::SessionID& sessionID ) [simplified] { QuickFix::Message * toMessage = create( message ); m_application->toApp( toMessage, new QuickFix::SessionID( sessionID ) ); message = toMessage->unmanaged(); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ } The solution is quite easy: (well, once you identify the problem... ;) Simply 'tag' all pointers to GC'ed classes with "__pin" keyword: QuickFix::Message __pin * toMessage = create( message ); The toMessage object stays locked in memory in the method body even if GC is activated. I have seen the problem only in toApp(), but I believe that toAdmin() is affected in the same way. Since 'pinning' a pointer for a short time does not hurt performance, I decided to 'pin' all QuickFix::Message pointers in the Application class. It is quite possible that other C#-to-C++ wrappers suffer from the same problem, but I have not analyzed them. Important note: I was unable to reproduce the problem while executing a QuickFIX application in Visual Studio.NET's debugger. The application must be executed stand-alone from the command line, because VS.NET changes the way the garbage collector works. Both Debug and Release builds produce the same erroneous behaviour. Here is the diff: --- Application.h 2004-05-31 15:27:42.000000000 +0200 +++ Application.h.new 2004-10-19 17:22:15.011923000 +0200 @@ -71,7 +71,7 @@ void toAdmin( FIX::Message& message, const FIX::SessionID& sessionID ) { - QuickFix::Message * toMessage = create( message ); + QuickFix::Message __pin * toMessage = create( message ); m_application->toAdmin( toMessage, new QuickFix::SessionID( sessionID ) ); message = toMessage->unmanaged(); } @@ -79,7 +79,7 @@ void toApp( FIX::Message& message, const FIX::SessionID& sessionID ) throw( FIX::DoNotSend& ) { - QuickFix::Message * toMessage = create( message ); + QuickFix::Message __pin * toMessage = create( message ); try { m_application->toApp( toMessage, new QuickFix::SessionID( sessionID ) ); @@ -95,7 +95,7 @@ FIX::IncorrectTagValue&, FIX::RejectLogon& ) { - QuickFix::Message * toMessage = create( message ); + QuickFix::Message __pin * toMessage = create( message ); try { m_application->fromAdmin @@ -122,7 +122,7 @@ FIX::IncorrectTagValue&, FIX::UnsupportedMessageType& ) { - QuickFix::Message * toMessage = create( message ); + QuickFix::Message __pin * toMessage = create( message ); try { m_application->fromApp @@ -153,7 +153,7 @@ FIX::MsgType msgType; unmanaged.getHeader().getField( beginString ); unmanaged.getHeader().getField( msgType ); - QuickFix::Message* message + QuickFix::Message __pin * message = m_factory->create ( beginString.getValue().c_str(), msgType.getValue().c_str() ); message->setUnmanaged( unmanaged ); Please put this patch to the official source tree ASAP. Cheers, Vlad ------------------------------------------------------------- Ing. Vladimir Arnost, Developer, FFastFill Europe Ltd. Vaclavske namesti 55, Prague, Czech Republic ________________________________________________________________________ This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify sec...@ff... This email has been scanned for all viruses by the FFastFill Email Security System. ________________________________________________________________________ ------------------------------------------------------- This SF.net email is sponsored by: IT Product Guide on ITManagersJournal Use IT products in your business? Tell us what you think of them. Give us Your Opinions, Get Free ThinkGeek Gift Certificates! 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