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Posted to dev@tomcat.apache.org by bu...@apache.org on 2016/03/23 14:17:59 UTC
[Bug 59220] New: AsyncListener#onComplete not called after timeout
if buffer is flushed
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
Bug ID: 59220
Summary: AsyncListener#onComplete not called after timeout if
buffer is flushed
Product: Tomcat 8
Version: 8.0.32
Hardware: PC
Status: NEW
Severity: normal
Priority: P2
Component: Catalina
Assignee: dev@tomcat.apache.org
Reporter: niscomar@googlemail.com
If an async dispatch cycle is started and a timeout occurs before the response
buffer is flushed using response#flushBuffer(), then the
AsyncListener#onTimeout()
method followed by the AsyncListener#onComplete() are correctly called.
However, if the buffer is flushed before the timeout occurs, the
AsyncListener#onTimeout() method will be called, but the
AsyncListener#onComplete() will not be.
A sample servlet demonstrating the problem, AsyncDebugListener, is provided
at the following location:
https://github.com/msnicklous/AsyncDebug
Build the AsyncDebugListener module using 'mvn install' and deploy it on
Tomcat.
The service method and each of the AsyncListener methods logs output to the
AsyncListener.log file. You can follow execution by looking at the logs.
Assuming Tomcat is installed locally, you can use the following URLs:
1) No timeout - works correctly:
http://localhost:8080/AsyncDebugListener/ltest?reps=3
2) Timeout, no flush - works correctly:
http://localhost:8080/AsyncDebugListener/ltest?reps=3&timeout
3) Flush before timeout - error case:
http://localhost:8080/AsyncDebugListener/ltest?reps=3&timeout&flush
>From the logs, you will see that AsyncListener#onTimeout() was called, but
AsyncListener#onComplete() was not.
Thanks for having a look at this!
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #3 from Scott Nicklous <ni...@googlemail.com> ---
Hi Violeta and Remy,
thank you very much for having a look at this so quickly (and thank you, Remy
for fixing 59213 so promptly!). The example servlets I provided were for the
purpose of reproducing the problem rather than for illustrating the use case. I
would like to explain my use case more clearly.
I'm working on the Apache Pluto project, which is the reference implementation
for JSR 286 Portlet Specification 2.0, and which will be the reference
implementation for JSR 362 Portlet Specification 3.0. Pluto is a minimal portal
server that implements the required API for portlet applications.
For version 3.0, we want to provide async support for portlet applications. The
portlet specification can make recommendations about how portlet applications
should do error handling, but can't really guarantee that the portlet apps will
follow the recommendations.
The Pluto server has to allocate resources to support the portlet applications
during async processing and needs a reliable way to release those resources
even if a timeout or error condition occurs. It seems to me that the natural
way to do that would be for the Pluto server to register an AsyncListener on
behalf of the portlet application in order to release the resources when
onComplete() is called.
However, this bug along with 59219 means that in these edge cases, Pluto will
not be able to release the resources, which could potentially result in a
memory leak.
That said, I understand that these really are edge cases, and I can't really
say how high the priority should be in the grand scheme of things. But it would
be very nice if they could be fixed at some point as time & priority allows.
:-)
thanks again,
Scott
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #11 from Mark Thomas <ma...@apache.org> ---
It is worth taking a look to see if we can get consistent behaviour with and
without flush. The client won't see the same result but hopefully the app will
be able to see a consistent set of events.
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
Mark Thomas <ma...@apache.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #13 from Mark Thomas <ma...@apache.org> ---
Fixed in:
- 9.0.x for 9.0.0.M5 onwards
- 8.5.x for 8.5.1 onwards
- 8.0.x for 8.0.34 onwards
- 7.0.x for 7.0.70 onwards
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #12 from Scott Nicklous <ni...@googlemail.com> ---
I would not see a problem in handling the SC=500 as long as onComplete() is
called. It would seem to me to be the specified behavior.
In the case of Pluto, the SC=500 along with any Tomcat-generated error text
would be passed to the client, which would give the portlet application
developers a nice clue that they need to fix their bug. :-)
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #9 from Scott Nicklous <ni...@googlemail.com> ---
In the specific case addressed by this bug report, both onTimeout() and
onComplete() are correctly called as long as the buffer is not flushed.
The problem occurs only when the buffer was flushed at least once before the
timeout occurs. If the buffer was flushed, onTimeout() is called, but
onComplete() is not.
If the buffer was flushed, I don't think Tomcat can set the status code or do
an error dispatch anymore. But it would be nice if onComplete() would be called
after the onTimeout() anyway.
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #10 from Violeta Georgieva <vi...@apache.org> ---
(In reply to Scott Nicklous from comment #9)
> In the specific case addressed by this bug report, both onTimeout() and
> onComplete() are correctly called as long as the buffer is not flushed.
>
> The problem occurs only when the buffer was flushed at least once before the
> timeout occurs. If the buffer was flushed, onTimeout() is called, but
> onComplete() is not.
>
> If the buffer was flushed, I don't think Tomcat can set the status code or
> do an error dispatch anymore. But it would be nice if onComplete() would be
> called after the onTimeout() anyway.
Actually it will as it is required by the spec
"
- Invoke the AsyncListener.onTimeout method on all the AsyncListener
instances registered with the ServletRequest on which the asynchronous
operation was initiated.
- If none of the listeners called AsyncContext.complete() or any of the
AsyncContext.dispatch methods, perform an error dispatch with a status
code equal to HttpServletResponse.SC_INTERNAL_SERVER_ERROR."
"GET /AsyncDebugListener/ltest?reps=3&timeout&flush HTTP/1.1" 500 642
"GET /AsyncDebugListener/ltest?reps=3&timeout HTTP/1.1" 500 624
This is what I will receive in the http access code with your example.
Regards,
Violeta
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #8 from Violeta Georgieva <vi...@apache.org> ---
If you wait for Tomcat to invoke a complete(), then this will be an error
situation and as it is per spec Tomcat will set the response code to 500. Isn't
that a problem from application point of view?
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
Violeta Georgieva <vi...@apache.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
OS| |All
--- Comment #1 from Violeta Georgieva <vi...@apache.org> ---
Hi,
Based on the example that you've provided I can say that you are in so called
"error dispatch" situation i.e.
"2.3.3.3 Asynchronous processing
- If none of the listeners called AsyncContext.complete or any of the
AsyncContext.dispatch methods, then perform an error dispatch with a
status code equal to HttpServletResponse.SC_INTERNAL_SERVER_ERROR
and make the Throwable available as the value of the
RequestDispatcher.ERROR_EXCEPTION request attribute.
- If no matching error page is found, or the error page does not call
AsyncContext.complete() or any of the AsyncContext.dispatch methods,
then the container MUST call AsyncContext.complete."
So when you do not perform flush the response is not committed and
org.apache.catalina.valves.ErrorReportValve.invoke(...) handles the situation
correctly and onComplete is called, but when you perform flush,
ErrorReportValve will mark the connection to be closed as the response is
committed and onComplete will not be invoked.
I'm thinking about whether we should delay this, but I would like to hear the
other committers' opinion.
For your use case my recommendation is to call AsyncContext.complete in your
listener and not to wait the container to call it for you.
Regards,
Violeta
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #6 from Violeta Georgieva <vi...@apache.org> ---
(In reply to Scott Nicklous from comment #5)
> I know what you mean and agree with you.
>
> From Tomcat's point of view, the Pluto portal is an application. However,
> Pluto itself hosts portlet applications that may come from various sources.
> The question is how can Pluto release its resources allocated to a portlet
> async request if the portlet application misbehaves or has an exception and
> does not call complete()?
>
> My idea was that Pluto could register an AsyncListener of its own (in
> addition to any AsyncListeners possibly registered by the portlet
> applications) to release its resources during the onComplete call. But that
> only works if the underlying container (Tomcat, in this case) assures that
> onComplete is called under all circumstances.
The idea here is that you should call AsyncContext.complete() in onTimeout
event that your listener will receive instead of waiting for container to call
AsyncContext.complete() and then onComplete().
In your example if I add AsyncContext.complete() in
basic.servlet.TestedListener.onTimeout(AsyncEvent) then the third use case is
working.
Do you think this will work for your scenario?
Regards,
Violeta
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #2 from Remy Maucherat <re...@apache.org> ---
That sounds like a logical explanation and 59219 sounds a bit similar. This is
all edge cases though and I doubt everything is well defined in the
specification. So it is best to not try it :)
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #5 from Scott Nicklous <ni...@googlemail.com> ---
I know what you mean and agree with you.
>From Tomcat's point of view, the Pluto portal is an application. However, Pluto
itself hosts portlet applications that may come from various sources. The
question is how can Pluto release its resources allocated to a portlet async
request if the portlet application misbehaves or has an exception and does not
call complete()?
My idea was that Pluto could register an AsyncListener of its own (in addition
to any AsyncListeners possibly registered by the portlet applications) to
release its resources during the onComplete call. But that only works if the
underlying container (Tomcat, in this case) assures that onComplete is called
under all circumstances.
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #7 from Scott Nicklous <ni...@googlemail.com> ---
Hi Violeta,
That would be a potential workaround for the timeout case. I would have to
ensure that the Pluto listener runs after all AsyncListeners registered by the
portlet applications.
It would be a little bit difficult to implement, since the servlet spec
requires that the listeners be called in the order in which they are
registered, and that's the way Tomcat works, too. So Pluto would not be able to
simply call startAsync, add its listener to the AsyncContext, and pass the
AsyncContext to the portlet application. I would probably have to wrap the
AsyncContext object in order to make sure that the Pluto listener is always the
last one added.
But it would be possible.
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[Bug 59220] AsyncListener#onComplete not called after timeout if
buffer is flushed
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59220
--- Comment #4 from Remy Maucherat <re...@apache.org> ---
The question is really about the cases where complete should be called for the
application (which didn't call it although it should have).
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