Thread synchronization error in TcpTransport
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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
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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