Re: [udig-dev] ConcurrentModificationException on MemoryDataStore Layer

[Jody Garnett <jody.garnett@xxxxxxxxx>]

In general we try and have a Transaction to keep seperate threads independent, but in this case we are both rendering from (and writing) to the same transaction.

I would not put any time into debugging this where you are at, The GeoTools 14.x series has been reviewed and approved by Eclipse IP process. This branch has migrated MemoryDataStore to ContendDataStore - so we are up against a new thing to test against.

As part of the migration Torben was able to poke a few holes in the Diff data structure used to keep transactions independent. I would expect that would be the correct location to resolve any concurrent modification problems.

--

Jody

--

Jody Garnett

On 7 September 2015 at 12:23, Frank Gasdorf <fgdrf@xxxxxxxxxxxxxxxxxxxxx> wrote:

Hi folks,

Sorry for cross-posting, I'm unsure which forum is the right choise to address this 

I'm wondering about the current behavior adding features programatically to a layer. The layer has a MemoryGeoResourceImpl internally which uses MemoryDataStore (geotools 11.2 & uDig 2.0.0-SNAPSHOT).

I expected to get features stored to DataStore while uDig is (still) rendering features already added. But the during rendering ConcurrentModificatinExtepion's are thrown while writing new features or modifying exiting.

!ENTRY org.locationtech.udig.project 2 0 2015-09-07 16:06:32.517
!MESSAGE class java.util.ConcurrentModificationException occured during rendering: null
!STACK 0
org.locationtech.udig.project.render.RenderException: class java.util.ConcurrentModificationException occured during rendering: null
    at org.locationtech.udig.render.internal.feature.basic.BasicFeatureRenderer.render(BasicFeatureRenderer.java:489)
    at org.locationtech.udig.render.internal.feature.basic.BasicFeatureRenderer.render(BasicFeatureRenderer.java:320)
    at org.locationtech.udig.project.internal.render.impl.RenderJob.startRendering(RenderJob.java:117)
    at org.locationtech.udig.project.internal.render.impl.RenderJob.run(RenderJob.java:222)
    at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)
Caused by: java.util.ConcurrentModificationException
    at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(Unknown Source)
    at java.util.LinkedHashMap$ValueIterator.next(Unknown Source)
    at org.geotools.data.memory.MemoryDataStore.getBounds(MemoryDataStore.java:609)
    at org.geotools.data.AbstractFeatureSource.getBounds(AbstractFeatureSource.java:318)
    at org.geotools.data.AbstractFeatureSource.getBounds(AbstractFeatureSource.java:286)
    at org.locationtech.udig.catalog.memory.internal.MemoryGeoResourceImpl$ScratchResourceInfo.getBounds(MemoryGeoResourceImpl.java:167)
    at org.locationtech.udig.project.internal.impl.GeoResourceInfoInterceptor$Wrapper.getBounds(GeoResourceInfoInterceptor.java:63)
    at org.locationtech.udig.project.internal.impl.LayerImpl.obtainBoundsFromResources(LayerImpl.java:2173)
    at org.locationtech.udig.project.internal.impl.LayerImpl.getBounds(LayerImpl.java:2144)
    at org.locationtech.udig.render.internal.feature.basic.BasicFeatureRenderer.validateBounds(BasicFeatureRenderer.java:567)
    at org.locationtech.udig.render.internal.feature.basic.BasicFeatureRenderer.render(BasicFeatureRenderer.java:363)
    ... 4 more

From a "user" perspective its quite hard to synchchronize access to the datastore while there are different extensions accessing the layer (getBounds, Iterator for Renderer, etc.) and its resources from uDig. I remember a discussion a few years ago about the same problem but cannot find the thread anymore.

Q: What's the best aproach to write features to MemoryDataStore while other having read-access in between? Would it be a good approach using a ConcurrentHashMap internally or using a different DataStore (e.g. h2)?

Thanks in advance

-- Frank

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