Fix MemKeyValueStore concurrency issue

org.nuxeo.ecm.core.bulk.TestSetPropertiesAction.testAbort
Failing for the past 1 build (Since Failed#177 )
Took 0.54 sec.
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Error Message

invoke on features error [Holder [type=class org.nuxeo.ecm.core.test.CoreFeature], Holder [type=class org.nuxeo.ecm.core.bulk.CoreBulkFeature], Holder [type=class org.nuxeo.ecm.core.io.CoreIOFeature], Holder [type=class org.nuxeo.ecm.core.work.WorkManagerFeature], Holder [type=class org.nuxeo.runtime.stream.RuntimeStreamFeature], Holder [type=class org.nuxeo.runtime.test.runner.TransactionalFeature], Holder [type=class org.nuxeo.runtime.test.runner.RuntimeFeature], Holder [type=class org.nuxeo.runtime.test.runner.RandomBug$Feature], Holder [type=class org.nuxeo.runtime.test.runner.ConditionalIgnoreRule$Feature], Holder [type=class org.nuxeo.runtime.test.runner.MDCFeature]]

Stacktrace

java.lang.AssertionError: invoke on features error [Holder [type=class org.nuxeo.ecm.core.test.CoreFeature], Holder [type=class org.nuxeo.ecm.core.bulk.CoreBulkFeature], Holder [type=class org.nuxeo.ecm.core.io.CoreIOFeature], Holder [type=class org.nuxeo.ecm.core.work.WorkManagerFeature], Holder [type=class org.nuxeo.runtime.stream.RuntimeStreamFeature], Holder [type=class org.nuxeo.runtime.test.runner.TransactionalFeature], Holder [type=class org.nuxeo.runtime.test.runner.RuntimeFeature], Holder [type=class org.nuxeo.runtime.test.runner.RandomBug$Feature], Holder [type=class org.nuxeo.runtime.test.runner.ConditionalIgnoreRule$Feature], Holder [type=class org.nuxeo.runtime.test.runner.MDCFeature]]
	at org.nuxeo.runtime.test.runner.FeaturesLoader.apply(FeaturesLoader.java:123)
	at org.nuxeo.runtime.test.runner.FeaturesLoader.apply(FeaturesLoader.java:113)
	at org.nuxeo.runtime.test.runner.FeaturesRunner.afterTeardown(FeaturesRunner.java:184)
	at org.nuxeo.runtime.test.runner.FeaturesRunner$AfterTeardownStatement.evaluate(FeaturesRunner.java:353)
...
	at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:417)
	Suppressed: java.util.ConcurrentModificationException
		at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1211)
		at java.util.TreeMap$KeyIterator.next(TreeMap.java:1265)
		at net.jodah.expiringmap.ExpiringMap$EntryTreeHashMap$AbstractHashIterator.getNext(ExpiringMap.java:473)
		at net.jodah.expiringmap.ExpiringMap$EntryTreeHashMap$KeyIterator.next(ExpiringMap.java:491)
		at java.util.Iterator.forEachRemaining(Iterator.java:116)
		at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
		at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
		at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
		at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
		at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
		at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
		at org.nuxeo.ecm.core.bulk.BulkServiceImpl.await(BulkServiceImpl.java:250)
		at org.nuxeo.ecm.core.bulk.CoreBulkFeature.lambda$initialize$0(CoreBulkFeature.java:45)
		at org.nuxeo.runtime.test.runner.TransactionalFeature.await(TransactionalFeature.java:121)
		at org.nuxeo.runtime.test.runner.TransactionalFeature.nextTransaction(TransactionalFeature.java:101)
		at org.nuxeo.runtime.test.runner.TransactionalFeature.nextTransaction(TransactionalFeature.java:77)
		at org.nuxeo.ecm.core.test.CoreFeature.waitForAsyncCompletion(CoreFeature.java:241)
		at org.nuxeo.ecm.core.test.CoreFeature.lambda$cleanupSession$1(CoreFeature.java:273)
		at org.nuxeo.runtime.transaction.TransactionHelper.lambda$runInNewTransaction$2(TransactionHelper.java:542)
		at org.nuxeo.runtime.transaction.TransactionHelper.runInTransaction(TransactionHelper.java:589)
		at org.nuxeo.runtime.transaction.TransactionHelper.runInNewTransaction(TransactionHelper.java:555)
		at org.nuxeo.runtime.transaction.TransactionHelper.runInNewTransaction(TransactionHelper.java:542)
		at org.nuxeo.ecm.core.test.CoreFeature.cleanupSession(CoreFeature.java:249)
		at org.nuxeo.ecm.core.test.CoreFeature.afterTeardown(CoreFeature.java:234)
		at org.nuxeo.runtime.test.runner.FeaturesRunner.lambda$afterTeardown$8(FeaturesRunner.java:184)
		at org.nuxeo.runtime.test.runner.FeaturesLoader.apply(FeaturesLoader.java:126)
		... 38 more

Standard Output

2018-11-29 18:58:30,670 [scrollerPool-01,in:2,inCheckpoint:2,out:2,lastRead:1543517909800,lastTimer:0,wm:202311979461771265,loop:33,checkpoint] WARN  [Slf4jExceptionHandler$2] Took 83 us to linearScan by position from 131328 to 132301 = (0x204cd-0x20100)=973