I agree that synchronization is not a good fix. It’s just a patch for my purposes for now and I mention it mostly to better confirm the scope of the problem. The binding class is org.geotools.filter.v2_0.bindings.BBOXTypeBinding…
From: andrea.aime@anonymised.com [mailto:andrea.aime@anonymised.com] On Behalf Of Andrea Aime
Sent: Monday, September 4, 2017 5:53 AM
To: Walter Stovall <walter.stovall@anonymised.com>; Niels Charlier <niels@anonymised.com>
Cc: geoserver-devel@anonymised.comsourceforge.net
Subject: Re: [Geoserver-devel] I’m a victim of GEOS-7961 NullPointer closed as cannot-reproduce but I make it happen all the time
Hi Walter,
I believe the synchronization you’re proposing is too wide and will cause significant scalability degradation,
a more localized solution needs to be searched.
Which binding class are you referring to? The one in org.geotools.filter.v2_0.bindings ?
(there are a few others, I believe this one would be used if you are doing WFS 2.0 requests only).
Regards
Andrea
On Sat, Sep 2, 2017 at 12:31 PM, Walter Stovall <walter.stovall@anonymised.com> wrote:
https://osgeo-org.atlassian.net/browse/GEOS-7961
This bug happens under load as a result of a multithreading bug in the implementation of BBOXTypeBinding.getProperties. More specifically, the partical.getContent() value there will be be corrupted/set to null by another thread executing that same code. I’m not certain what the correct fix is yet but I do have some good detail and can make it fail every time. I’m hoping that somebody with more knowledge on the XSD classes might have some insight that would help reach a solution.
I encounter this bug very reliably by running a jMeter ThreadGroup that sends concurrent GetFeature requests that include a BBOX filter. I’ve since then figured out how to repro the bug in eclipse and identified a fairly narrow scope of code that is the root of the problem.
To repro this problem in eclipse place a breakpoint in BBOXTypeBinding.getProperties at the following code:
particle.setContent(GML.getInstance().getSchema().resolveElementDeclaration(GML.Envelope.getLocalPart()));
particle.setMinOccurs(0);
Put the breakpoint on the particle.setMinOccurs call right after the above call to setContent.
Now execute the GetFeature request and hit the breakpoint. Note that as expected the particle.getContent() value at this point is not null, as it was set by the proceeding line of code.
Now while sitting on that breakpoint execute another GetFeature and stop there on the other thread. Again the value of particle.getContent() is not null. But go to the original breakpoint in the first thread and see that particle.getContent() IS NOW NULL!
In other words a GetFeature started on another thread has changed the particle.getContent() of the original thread. NullPointer exceptions like that shown in GEOS-7961 and others are now the result.
Digging deeper I see that each thread has a unique “particle” instance (particle on one thread refers to a different object than particle on another thread) – as expected since the object is obtained from the factory on entry to getProperties. But in scenarios where this code works successfully (not forced to fail as above) it’s at least interesting that the value of particle.getContent() is the very same object instance on both threads.
Ultimately the root of the problem has to do with the EObjectImpl.eContainer member – this is the object to which each particle refers.
While I don’t know what the best fix is, I do how to make this specific failure never happen. I patched my code as follows by adding the thread synchronization you see below in GetFeature…
synchronized(GetFeature.class) {
Encoder e = new Encoder(new FESConfiguration());
e.setOmitXMLDeclaration(true);
filter.append(e.encodeAsString(q.getFilter(), FES.Filter));
}
A more targeted fix would of course be much better and might address potential failures other than GetFeature. I’m not sure what the right fix is but it would appear to be centered on the behavior of the following, which is rather convoluted for my brain to fully digest when considering changes.
if (content != null)
msgs = ((InternalEObject)content).eInverseRemove(this, EOPPOSITE_FEATURE_BASE - XSDPackage.XSD_PARTICLE__CONTENT, null, msgs);
if (newContent != null)
msgs = ((InternalEObject)newContent).eInverseAdd(this, EOPPOSITE_FEATURE_BASE - XSDPackage.XSD_PARTICLE__CONTENT, null, msgs);
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Andrea Aime
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@geowolf
Technical Lead
GeoSolutions S.A.S.
Via di Montramito 3/A
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fax: +39 0584 1660272
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AVVERTENZE AI SENSI DEL D.Lgs. 196/2003
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The information in this message and/or attachments, is intended solely for the attention and use of the named addressee(s) and may be confidential or proprietary in nature or covered by the provisions of privacy act (Legislative Decree June, 30 2003, no.196 - Italy’s New Data Protection Code).Any use not in accord with its purpose, any disclosure, reproduction, copying, distribution, or either dissemination, either whole or partial, is strictly forbidden except previous formal approval of the named addressee(s). If you are not the intended recipient, please contact immediately the sender by telephone, fax or e-mail and delete the information in this message that has been received in error. The sender does not give any warranty or accept liability as the content, accuracy or completeness of sent messages and accepts no responsibility for changes made after they were sent or for other risks which arise as a result of e-mail transmission, viruses, etc.