Re: [xSocket-develop] Simple Server Sometimes Seeing Data Corruption on Client Side
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Re: [xSocket-develop] Simple Server Sometimes Seeing Data Corruption on Client Side
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From: Rod M. <rod...@gm...> - 2008-05-05 06:49:14
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While the synchronizing on the connections eliminated the NPE I saw when
trying to construct a test case, I'm still getting the data corruption
issue. I can't get my Java to Java test case to repro it, so looks like it's
on the Flash side, though it's hard to believe there are issues like this in
XMLSocket. Will continue to investigate.
Thanks again,
Rod
On Sun, May 4, 2008 at 11:38 AM, Rod Magnuson <rod...@gm...> wrote:
> Thank you!
>
> The tutorial update was great. Appreciate your help.
>
> Rod
>
>
> On Sun, May 4, 2008 at 1:04 AM, Gregor Roth <gre...@go...>
> wrote:
>
>> Hi Rod,
>>
>> yes, the NonBlockingConnection and BlockingConnection are not thread safe.
>> This means, you have to synchronize concurrent method calls. xSocket only
>> guarantees that the call back methods will be executed in a synchronized,
>> serialized manner.
>>
>> The NullPointerException is caused by unsynchronized, concurrent write
>> calls on the same connection (-> sendMessageToAllClients will be called
>> concurrently) .
>>
>>
>> May be it would make sense to enhance the ConnectionUtils by a
>> synchronizedConnection(INonBlockingConnection nbc) and a
>> synchronizedConnection(IBlockingConnection con) method. But his doesn't help
>> if concurrent threads will execute code like:
>>
>> con.markWritePosition();
>>
>> con.write(..);
>>
>> con.resetToWriteMark();
>>
>>
>> For this reason I'm not sure if it is a good idea to provide synchronized
>> connections. This will give the feeling of thread safety which fails if you
>> using statements like above.
>>
>> I updated the tutorial by this subject
>>
>>
>> Gregor
>>
>>
>>
>>
>>
>>
>> 2008/5/3 Rod Magnuson <rod...@gm...>:
>>
>>> While trying to get a simple test that fails I ran into:
>>>
>>> java.lang.NullPointerException:
>>> Exception in thread "xServerPool-1-thread-8"
>>> java.lang.NullPointerException
>>> at org.xsocket.connection.WriteQueue.append(WriteQueue.java:133)
>>> at
>>> org.xsocket.connection.AbstractNonBlockingStream.write(AbstractNonBlockingStream.java:1060)
>>> at
>>> org.xsocket.connection.AbstractNonBlockingStream.write(AbstractNonBlockingStream.java:1040)
>>> at testproject.TestServer.sendMessageToAllClients(TestServer.java:73)
>>> at testproject.TestServer.onData(TestServer.java:63)
>>> at
>>> org.xsocket.connection.HandlerAdapter.onData(HandlerAdapter.java:132)
>>> at
>>> org.xsocket.connection.MultithreadedHandlerAdapter.access$201(MultithreadedHandlerAdapter.java:38)
>>> at
>>> org.xsocket.connection.MultithreadedHandlerAdapter$2.run(MultithreadedHandlerAdapter.java:80)
>>> at
>>> org.xsocket.SerializedTaskQueue.performPendingTasks(SerializedTaskQueue.java:113)
>>> at
>>> org.xsocket.SerializedTaskQueue.access$100(SerializedTaskQueue.java:38)
>>> at
>>> org.xsocket.SerializedTaskQueue$MultithreadedTaskProcessor.run(SerializedTaskQueue.java:139)
>>> at
>>> java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
>>> at
>>> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
>>> at java.lang.Thread.run(Thread.java:619)
>>>
>>> Which made me think perhaps I'm lacking some basic understanding, since I
>>> see zero synchronization in the call chain down from connection.write. Am I
>>> supposed to provide this synchronization?
>>>
>>> Thanks,
>>> Rod
>>>
>>> Here's what my test server looks like:
>>>
>>> package testproject;
>>>
>>> import java.io.IOException;
>>> import java.io.UnsupportedEncodingException;
>>>
>>> import java.net.SocketTimeoutException;
>>>
>>> import java.nio.channels.ClosedChannelException;
>>>
>>> import java.util.concurrent.ConcurrentHashMap;
>>>
>>> import org.xsocket.connection.ConnectionUtils;
>>> import org.xsocket.connection.IConnectHandler;
>>> import org.xsocket.connection.IConnection;
>>> import org.xsocket.connection.IDataHandler;
>>> import org.xsocket.connection.IDisconnectHandler;
>>> import org.xsocket.connection.INonBlockingConnection;
>>> import org.xsocket.connection.Server;
>>>
>>>
>>> public class TestServer
>>> implements IConnectHandler, IDisconnectHandler, IDataHandler
>>> {
>>> public static final String END_OF_MESSAGE_DELIM = new String(new char[]
>>> { 0 });
>>> // public static final String END_OF_MESSAGE_DELIM = "\r";
>>>
>>> public static void main(String[] args)
>>> {
>>> try
>>> {
>>> final Server server = new Server(6000, new TestServer());
>>> server.setFlushMode(IConnection.FlushMode.ASYNC);
>>>
>>> ConnectionUtils.start(server);
>>> }
>>> catch (Exception e)
>>> {
>>> e.printStackTrace();
>>> }
>>> }
>>>
>>> public boolean onConnect(INonBlockingConnection connection)
>>> {
>>> connection.setAutoflush(false);
>>> m_Connections.put(connection, Boolean.TRUE);
>>> return true;
>>> }
>>>
>>> public boolean onDisconnect(INonBlockingConnection connection)
>>> {
>>> m_Connections.remove(connection);
>>> return true;
>>> }
>>>
>>> public boolean onData(INonBlockingConnection connection)
>>> throws IOException, UnsupportedEncodingException
>>> {
>>> // reset to read position (if former reads failed) and mark it
>>> connection.resetToReadMark();
>>> connection.markReadPosition();
>>>
>>> final String message =
>>> connection.readStringByDelimiter(END_OF_MESSAGE_DELIM);
>>>
>>> connection.removeReadMark();
>>>
>>> sendMessageToAllClients("<received>" + message + "</received>");
>>>
>>> return true;
>>> }
>>>
>>> private void sendMessageToAllClients(String message)
>>> throws ClosedChannelException, IOException, SocketTimeoutException
>>> {
>>> for (INonBlockingConnection connection : m_Connections.keySet())
>>> {
>>> connection.write(message + END_OF_MESSAGE_DELIM);
>>> connection.flush();
>>> }
>>> }
>>>
>>> private final ConcurrentHashMap<INonBlockingConnection, Boolean>
>>> m_Connections = new ConcurrentHashMap<INonBlockingConnection, Boolean>();
>>>
>>> }
>>>
>>>
>>> On Sat, May 3, 2008 at 12:43 AM, Gregor Roth <gre...@go...>
>>> wrote:
>>>
>>>> Hi Rod,
>>>>
>>>> would you please submit this as a bug (
>>>> http://sourceforge.net/tracker/?atid=850942&group_id=169583). Please
>>>> also add a junit test, which contains the essential xSocket-related part of
>>>> your client and server-side code.
>>>>
>>>> Thanks
>>>> Gregor
>>>>
>>>> 2008/5/3 Rod Magnuson <rod...@gm...>:
>>>>
>>>>> I've got a simple server that sends/receives null terminated Strings
>>>>> to/from a flash based client.
>>>>>
>>>>>
>>>>> Flush mode is async.
>>>>>
>>>>> I'm using the 2.0 final jar.
>>>>>
>>>>> I'm seeing times when the client is receiving mangled data. The length
>>>>> of the data is correct, just some of the contents are wrong. This does not
>>>>> happen often and is hard to reproduce. When it does happen other clients
>>>>> receive the correct data.
>>>>>
>>>>> I write out the messages with:
>>>>>
>>>>> String END_OF_MESSAGE_DELIM = new String(new char[] { 0 });
>>>>> connection.write(message + END_OF_MESSAGE_DELIM);
>>>>> connection.flush();
>>>>>
>>>>> It could be either client or server. Ideas on how to disqualify the
>>>>> server?
>>>>>
>>>>> Thanks,
>>>>> Rod
>>>>>
>>>>>
>>>>> -------------------------------------------------------------------------
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>>>>> _______________________________________________
>>>>> xSocket-develop mailing list
>>>>> xSo...@li...
>>>>> https://lists.sourceforge.net/lists/listinfo/xsocket-develop
>>>>>
>>>>>
>>>>
>>>>
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>>>>
>>>
>>
>
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