Hi,
Did you synchronize the event.close() with same lock you use to write to
the output stream (the SynchronizedOuputStream instance)?
I saw exactly the same stack trace you are getting due to (incorrect)
concurrent access to the CoyoteOutputStream. The NullPointerException
suggest that the request has already been cleaned up/recycled and yet
you still write to it. Make sure that when you close the event, either
the write becomes a null operation, or better, does not get called. It
is a bug to call write on the response output stream after the event has
been closed.
With the SynchronizedOutputStream construction I am relying on Tomcat
not to close or call any methods on the CoyoteOutputStream outside of
the CometProcessor's event() method. I don't know if this is correct (it
has worked for me in practice so far, and I've been doing some heavy
duty testing); however I do not know what else I could synchronize on.
If anybody knows a better approach, I would like to know. :-)
Regards,
Sebastiaan
Martin Perez wrote:
Hi,
Thanks for the tip Sebastian, but it doesn't work for me. I added your
class, wrapped all the output streams and synchronized close events
but the
result is the same.
Exception in thread "MessageSender[]" java.lang.NullPointerException
at org.apache.coyote.http11.InternalNioOutputBuffer.addToBB(
InternalNioOutputBuffer.java:607)
at org.apache.coyote.http11.InternalNioOutputBuffer.commit(
InternalNioOutputBuffer.java:600)
at org.apache.coyote.http11.Http11NioProcessor.action(
Http11NioProcessor.java:1032)
at org.apache.coyote.Response.action(Response.java:181)
at org.apache.coyote.http11.InternalNioOutputBuffer.doWrite(
InternalNioOutputBuffer.java:571)
at org.apache.coyote.Response.doWrite(Response.java:560)
at org.apache.catalina.connector.OutputBuffer.realWriteBytes(
OutputBuffer.java:353)
at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java
:434)
at org.apache.tomcat.util.buf.ByteChunk.append(ByteChunk.java:349)
at org.apache.catalina.connector.OutputBuffer.writeBytes(
OutputBuffer.java:381)
at org.apache.catalina.connector.OutputBuffer.write(
OutputBuffer.java:370)
at org.apache.catalina.connector.CoyoteOutputStream.write(
CoyoteOutputStream.java:89)
at org.apache.catalina.connector.CoyoteOutputStream.write(
CoyoteOutputStream.java:83)
at com.cognotec.streaming.SynchronizedOutputStream.write(
SynchronizedOutputStream.java:25)
at com.cognotec.streaming.CometRateSender.run(CometRateSender.java
:86)
at java.lang.Thread.run(Thread.java:595)
(As I said, I also synchronized all the close method calls either in
stream
either in comet event)
So, the question is: Is this a bug or simply I have reached the
scalability
limit for my box?
Cheers,
Martin
On 4/30/07, Sebastiaan van Erk <[EMAIL PROTECTED]> wrote:
Hi,
I had the same problems. It was a synchronization issue with me. What I
did was make a synchronized output stream wrapper (see attached file)
which wraps all access to the output stream, and I synchronized on this
output stream whenever I called event.close() on the Comet event
(especially in the READ event). When doing serveral IO operations on the
output stream which should not be interrupted, you can simply
synchronize on it (since SynchronizedOutputStream locks on itself).
Regards,
Sebastiaan
Martin Perez wrote:
> Hi all,
>
> I have been testing Tomcat comet support during the last days. I've
> created
> a test application that simulates data streaming to multiple clients.
> Clients open a connection to the server and the connection is hold
> open. In
> the server there are several "sender" threads that leverage comet
> support to
> periodically send stream updates to the subscribed clients. Once a
client
> receives a specified amount of data the communication is closed.
>
> So, I'm running the test with tomcat svn version from 1 week ago. I
have
> configured 150 tomcat threads, plus 25 acceptor threads. Tomcat
runs in
a
> Sun-Fire-V240 box with 2 CPU cores. I have 75 sender threads that
> periodically sleep (100ms) to try to reduce the CPU usage. Once a
sender
> thread wakes up, it will send all the data to the assigned clients.
>
> So basically the story is that the box is able to manage about 3500
> persistent comet connections smoothly. But when I raise the level to
4000
> (80% CPU usage, 1.2G mem.) I start to get these exceptions for some
(not
> all) connections:
>
> Exception in thread "MessageSender[]" java.lang.NullPointerException
> at org.apache.coyote.http11.InternalNioOutputBuffer.addToBB(
> InternalNioOutputBuffer.java:607)
> at org.apache.coyote.http11.InternalNioOutputBuffer.commit(
> InternalNioOutputBuffer.java:600)
> at org.apache.coyote.http11.Http11NioProcessor.action(
> Http11NioProcessor.java:1032)
> at org.apache.coyote.Response.action(Response.java:181)
> at org.apache.coyote.http11.InternalNioOutputBuffer.doWrite(
> InternalNioOutputBuffer.java:571)
> at org.apache.coyote.Response.doWrite(Response.java:560)
> at org.apache.catalina.connector.OutputBuffer.realWriteBytes(
> OutputBuffer.java:353)
> at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(
ByteChunk.java
> :434)
> at org.apache.tomcat.util.buf.ByteChunk.append(ByteChunk.java
:349)
> at org.apache.catalina.connector.OutputBuffer.writeBytes(
> OutputBuffer.java:381)
> at org.apache.catalina.connector.OutputBuffer.write(
> OutputBuffer.java:370)
> at org.apache.catalina.connector.CoyoteOutputStream.write(
> CoyoteOutputStream.java:89)
> at org.apache.catalina.connector.CoyoteOutputStream.write(
> CoyoteOutputStream.java:83)
> at com.cognotec.streaming.CometRateSender.run(
CometRateSender.java
> :86)
> at java.lang.Thread.run(Thread.java:595)
>
> So well, does anybody knows what can be the problem? Any suggestions?
> It can
> be also my problem, so I will be happy to provide more information.
>
> Cheers,
> Martin
>
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