ConcurrentModificationException while destroying single resources

[tfr42]

Currently the integration tests fail in module "deegree-resource-deps-tests" due to the following errors:

16:15:38]  INFO: [CRSManager] Clear CRS store and transformation map
[16:15:38]  INFO: [CRSManager] --------------------------------------------------------------------------------
[16:15:38]  INFO: [CRSManager] No 'crs' directory -- use default configuration.
[16:15:38]  INFO: [CRSManager] --------------------------------------------------------------------------------
[16:15:38]  INFO: [CRSManager] Setting up crs store 'default' from file 'file:/var/jenkins_home/workspace/deegree-build-upload/deegree-core/deegree-core-cs/target/deegree-core-cs-3.4.14-SNAPSHOT.jar!/org/deegree/cs/persistence/default.xml'...
[16:15:38]  INFO: [CRSManager] Registering global crs store with id 'default', type: 'org.deegree.cs.persistence.deegree.d3.DeegreeCRSStore'
[ERROR] Tests run: 8, Failures: 0, Errors: 3, Skipped: 0, Time elapsed: 8.576 s <<< FAILURE! - in org.deegree.workspace.SimpleSqlFeatureStoreTest
[ERROR] testDestroyInitializeSingle(org.deegree.workspace.SimpleSqlFeatureStoreTest)  Time elapsed: 0.966 s  <<< ERROR!
java.util.ConcurrentModificationException
	at org.deegree.workspace.SimpleSqlFeatureStoreTest.testDestroyInitializeSingle(SimpleSqlFeatureStoreTest.java:156)

[ERROR] testDestroySingle(org.deegree.workspace.SimpleSqlFeatureStoreTest)  Time elapsed: 0.976 s  <<< ERROR!
java.util.ConcurrentModificationException
	at org.deegree.workspace.SimpleSqlFeatureStoreTest.testDestroySingle(SimpleSqlFeatureStoreTest.java:144)

[ERROR] testReinitializeChain(org.deegree.workspace.SimpleSqlFeatureStoreTest)  Time elapsed: 0.665 s  <<< ERROR!
java.util.ConcurrentModificationException
	at org.deegree.workspace.SimpleSqlFeatureStoreTest.testReinitializeChain(SimpleSqlFeatureStoreTest.java:170)

[INFO] 
[INFO] Results:
[INFO] 
[ERROR] Errors: 
[ERROR]   SimpleSqlFeatureStoreTest.testDestroyInitializeSingle:156 » ConcurrentModification
[ERROR]   SimpleSqlFeatureStoreTest.testDestroySingle:144 » ConcurrentModification
[ERROR]   SimpleSqlFeatureStoreTest.testReinitializeChain:170 » ConcurrentModification
[INFO] 
[ERROR] Tests run: 8, Failures: 0, Errors: 3, Skipped: 0

[lgoltz]

Testfailures are caused by a change in https://github.com/deegree/deegree3/pull/1058/files#diff-41768028a4f464394c40f29346f004f1121204b40501c7e168d6ee04fa592d98
Adds: graph.removeNode( id )
This removes nodes from the graph while other (dependents of the resource to destroy) are accessed.

First try:

1. Collecting all resources to remove
2. Remove collected resources

This leads to a NPE in org.deegree.workspace.SimpleSqlFeatureStoreTest#testDestroyInitializeSingle():

org.deegree.workspace.ResourceInitException: Unable to build resource FeatureStoreProvider:simplesql-ok: null

	at org.deegree.workspace.standard.DefaultWorkspace.init(DefaultWorkspace.java:398)
	at org.deegree.workspace.SimpleSqlFeatureStoreTest.testDestroyInitializeSingle(SimpleSqlFeatureStoreTest.java:158)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
...
Caused by: java.lang.NullPointerException
	at org.deegree.feature.persistence.simplesql.DbFeatureUtils.determineFeatureType(DbFeatureUtils.java:110)
	at org.deegree.feature.persistence.simplesql.SimpleSQLFeatureStore.init(SimpleSQLFeatureStore.java:419)
	at org.deegree.workspace.standard.DefaultWorkspace.init(DefaultWorkspace.java:388)
	... 25 more

It seems that the the dependent JDBCConnection is not Initialised as expected.

[tfr42]

After further analysis of the problem the TMC has the motion to resolve the ConcurrentModificationException not by removing the code changes and let an entry remain on the graph
Instead we favor to synchronize the access to the internal state of class org.deegree.workspace.standard.DefaultWorkspace

@copierrj I'll prepare a PR that adds synchronized to the appropriate places

[tfr42]

This issue still needs further investigation and a more reliable solution. A PR is under way #1099.