Fix potential ConcurrentModificationException during parallel load.

Access the SourceLevelURIsAdapter before the ParallelResourceLoader
starts as there can be ConcurrentModificationExceptions if one thread
modifies the adapters list while another constructs its thread local
resource set.

com.avaloq.tools.ddk.xtext.builder/src/com/avaloq/tools/ddk/xtext/builder/resourceloader/ParallelResourceLoader.java

@@ -159,12 +159,14 @@ public ParallelLoadOperation(final ResourceSet parent, final IProject project) {
       } else {
         this.resourceQueue = new ArrayBlockingQueue<Triple<URI, Resource, Throwable>>(queueSize);
       }
+      final boolean parentIsIndexing = BuildPhases.isIndexing(parent);
+      final Set<URI> parentSourceLevelUris = SourceLevelURIsAdapter.findInstalledAdapter(parent).getSourceLevelURIs();
       this.resourceSetProvider = new ThreadLocal<ResourceSet>() {
         @Override
         protected ResourceSet initialValue() {
           ResourceSet resourceSet = getResourceSetProvider().get(project);
-          BuildPhases.setIndexing(resourceSet, BuildPhases.isIndexing(parent));
-          SourceLevelURIsAdapter.setSourceLevelUrisWithoutCopy(resourceSet, SourceLevelURIsAdapter.findInstalledAdapter(parent).getSourceLevelURIs());
+          BuildPhases.setIndexing(resourceSet, parentIsIndexing);
+          SourceLevelURIsAdapter.setSourceLevelUrisWithoutCopy(resourceSet, parentSourceLevelUris);
           resourceSet.getLoadOptions().putAll(parent.getLoadOptions());
           // we are not loading as part of a build
           resourceSet.getLoadOptions().remove(ResourceDescriptionsProvider.NAMED_BUILDER_SCOPE);