Bug 567171 - fix synchronization issue in DeltaProcessingState

Fix problem introduced in Bug 431275. Synchronized on a field always
uses the object. It does not make sense if you assign a new object to
the field.

Change-Id: I7835bc1c92b9962c3aa811d6b6e5db4c578d91d6
Signed-off-by: Carsten Hammer <[email protected]>
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/168851
Tested-by: JDT Bot <[email protected]>
Reviewed-by: Jörg Kubitz <[email protected]>
Reviewed-by: Andrey Loskutov <[email protected]>

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/DeltaProcessingState.java

@@ -122,6 +122,7 @@ public void doNotUse() {
 	 * This is null if no refresh is needed.
 	 */
 	private Set<IJavaElement> externalElementsToRefresh;
+	private final Object mutex = new Object();
 
 	/*
 	 * Need to clone defensively the listener information, in case some listener is reacting to some notification iteration by adding/changing/removing
@@ -187,7 +188,7 @@ public DeltaProcessor getDeltaProcessor() {
 	}
 
 	public ClasspathChange addClasspathChange(IProject project, IClasspathEntry[] oldRawClasspath, IPath oldOutputLocation, IClasspathEntry[] oldResolvedClasspath) {
-		synchronized (this.classpathChanges) {
+		synchronized (this.mutex) {
 			ClasspathChange change = this.classpathChanges.get(project);
 			if (change == null) {
 				change = new ClasspathChange((JavaProject) JavaModelManager.getJavaModelManager().getJavaModel().getJavaProject(project), oldRawClasspath, oldOutputLocation, oldResolvedClasspath);
@@ -205,13 +206,13 @@ public ClasspathChange addClasspathChange(IProject project, IClasspathEntry[] ol
 	}
 
 	public ClasspathChange getClasspathChange(IProject project) {
-		synchronized (this.classpathChanges) {
+		synchronized (this.mutex) {
 			return this.classpathChanges.get(project);
 		}
 	}
 
 	public Map<IProject, ClasspathChange> removeAllClasspathChanges() {
-		synchronized (this.classpathChanges) {
+		synchronized (this.mutex) {
 			Map<IProject, ClasspathChange> result = this.classpathChanges;
 			this.classpathChanges = new LinkedHashMap<>(result.size());
 			return result;