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From "Rob Lugt (JIRA)" <j...@apache.org>
Subject [jira] Updated: (AMQ-988) Thread synchronization error in TcpTransport
Date Tue, 24 Oct 2006 09:12:02 GMT
     [ https://issues.apache.org/activemq/browse/AMQ-988?page=all ]

Rob Lugt updated AMQ-988:
-------------------------

    Attachment: amq988-patch.txt

Please apply the attached patch, which fixes a bug in OpenWireBinaryReader.ReadString.

This bug involves an incorrect call of the Read(byte[] buffer, int index, int count) method.
 Teh function requires that exactly the specified number of bytes are read from the input
stream, but the way it is currently written it will read any amount up to the specified number
of bytes (depending on what data is available in the socket input buffer).  

The result of this bug is a corrupt message when the required data is not in the socket input
buffer (which, for me, happens as soon as the message rate exceeds 100 msgs per second). 
The read-loop thread terminates and no further messages are received.

This is the true underlying cause of this bug.  The earlier analysis on threading appears
tro be superfluous (but it's probably worth keeping the dual NetworkStreams as this class
is not advertised as threrad-safe).

Regards
Rob Lugt


> 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: Rob Lugt
>             Fix For: 4.1
>
>         Attachments: amq988-patch.txt
>
>
> 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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