[jira] Resolved: (AMQ-988) Thread synchronization error in TcpTransport

["james strachan (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/activemq/browse/AMQ-988?page=all ]

james strachan resolved AMQ-988.
--------------------------------

    Fix Version/s: 4.1
       Resolution: Fixed

Great catch Rob! Patch applied with huge thanks

> Thread synchronization error in TcpTransport
> --------------------------------------------
>
>                 Key: AMQ-988
>                 URL: https://issues.apache.org/activemq/browse/AMQ-988
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: NMS (C# client)
>    Affects Versions: 4.0.2
>         Environment: Windows
>            Reporter: Rob Lugt
>         Assigned To: james strachan
>             Fix For: 4.1
>
>
> I have a problem where my C# client application crashes when placed under load.  It's taken a while to get to the bottom of it, but I believe I have identified the problem and luckily there's a simple solution.
> The AMQ .Net client uses a common pattern where a full-duplex TCP/IP connection is established with the broker, and the client uses two threads to concurrently read and write data to/from the underlying socket - one thread reading from a Reader object and the other writing to a Writer object.
> The TcpTransport.Start() method contains the following:-
>   NetworkStream networkStream = new NetworkStream(socket);
>   socketWriter = new OpenWireBinaryWriter(networkStream);
>   socketReader = new OpenWireBinaryReader(networkStream);
> This pattern is explicitly allowed in Java and Win32 applications, but .Net is a little vague on the subject.  The Microsoft documentation [1] suggests use of the asynchronous read/write calls for multithreaded applications, but that would significantly complicate the C# client which relies on blocking stream behaviour.  On the same doc page 
> Microsoft does specifiy that the Socket class is thread-safe, which I take to mean that concurrent read/write calls are permitted, however the same is not true of NetworkStream [2].
> Perhaps it would be reasonable to expect NetworkStream to have no internal state other than the Socket it contains, but apparently this is not the case because I've identified that it is a corrupt NetworkStream which is causing my application to crash under load.  After some experimentation and a fair amount of load testing, I think the solution is a simple change to the TcpTransport.start() method to use a separate NetworkStream for input and output operations. e.g. :-
>   NetworkStream inputNetworkStream = new NetworkStream(socket);
>   NetworkStream outputNetworkStream = new NetworkStream(socket);
>   socketWriter = new OpenWireBinaryWriter(inputNetworkStream);
>   socketReader = new OpenWireBinaryReader(outputNetworkStream);
> This works for me and my test client has now been running for 16 hours without crashing (before it would rarely last longer than 10 minutes).
> Regards
> Rob Lugt
> [1] http://msdn2.microsoft.com/en-us/library/system.net.sockets.socket.aspx
> [2] http://msdn2.microsoft.com/en-us/library/system.net.sockets.networkstream.aspx

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