Hi Water,
thank you for confirming the class. Git reports this code has been added by
Niels (cc'ed) as part of the
WFS-NG development effort.
Niels, XSD is not thread safe and based on EMF, which has the ugly tendency
to change both sides
of a relationship when a setter is called (e.g., bean A sets B as value,
and the EMF automation also
makes B point to A), this is rife with side effects.
That's why normally the code manipulating XSD items is either locked in an
single shot initialization
or protected with synchronizations.
However this particle creation is straight inside multithreaded access path
instead:
https://github.com/geotools/geotools/blame/master/modules/extension/xsd/xsd-fes/src/main/java/org/geotools/filter/v2_0/bindings/BBOXTypeBinding.java#L91
I am wondering, is there any specific reason why it's there? Could it be
moved to a static initializer instead?
Cheers
Andrea
On Mon, Sep 4, 2017 at 12:21 PM, Walter Stovall <[email protected]>
wrote:
> 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:* [email protected] [mailto:[email protected]] *On Behalf
> Of *Andrea Aime
> *Sent:* Monday, September 4, 2017 5:53 AM
> *To:* Walter Stovall <[email protected]>; Niels Charlier <
> [email protected]>
> *Cc:* [email protected]
> *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 <[email protected]>
> 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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>
>
>
> --
>
> Regards,
>
> Andrea Aime
>
> ==
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> Ing. Andrea Aime
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>
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==
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Ing. Andrea Aime
@geowolf
Technical Lead
GeoSolutions S.A.S.
Via di Montramito 3/A
55054 Massarosa (LU)
phone: +39 0584 962313
fax: +39 0584 1660272
mob: +39 339 8844549
http://www.geo-solutions.it
http://twitter.com/geosolutions_it
AVVERTENZE AI SENSI DEL D.Lgs. 196/2003
Le informazioni contenute in questo messaggio di posta elettronica e/o
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loro utilizzo è consentito esclusivamente al destinatario del messaggio,
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messaggio senza esserne il destinatario, Vi preghiamo cortesemente di
darcene notizia via e-mail e di procedere alla distruzione del messaggio
stesso, cancellandolo dal Vostro sistema. Conservare il messaggio stesso,
divulgarlo anche in parte, distribuirlo ad altri soggetti, copiarlo, od
utilizzarlo per finalità diverse, costituisce comportamento contrario ai
principi dettati dal D.Lgs. 196/2003.
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
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made after they were sent or for other risks which arise as a result of
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