Issue 22191. Grab the document lock before positionsLock to prevent deadlock.

editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/text/editor/SemanticHighlightingManager_NEW.java

Index: editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/text/editor/SemanticHighlightingManager_NEW.java
diff --git a/editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/text/editor/SemanticHighlightingManager_NEW.java b/editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/text/editor/SemanticHighlightingManager_NEW.java
index 9a66fd1d0ca4a63294b7ece482b77aa6a58d9679..996da72e7768a12384b3dc3398d2353316738ed3 100644
--- a/editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/text/editor/SemanticHighlightingManager_NEW.java
+++ b/editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/text/editor/SemanticHighlightingManager_NEW.java
@@ -33,6 +33,7 @@ import org.eclipse.jface.text.DocumentEvent;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.IPositionUpdater;
 import org.eclipse.jface.text.IRegion;
+import org.eclipse.jface.text.ISynchronizable;
 import org.eclipse.jface.text.ITextPresentationListener;
 import org.eclipse.jface.text.Position;
 import org.eclipse.jface.text.TextPresentation;
@@ -335,11 +336,26 @@ public class SemanticHighlightingManager_NEW implements AnalysisServerHighlights
       HighlightRegion highlight = highlights[i];
       newPositions[i] = new HighlightPosition(highlight);
     }
-    synchronized (positionsLock) {
-      lastText = document.get();
-      lastRegions = highlights;
-      positions = newPositions;
+    synchronized (getDocumentLockObject()) {

[Paul Berry, 2015/01/28 18:30:22]

It would be nice to have a comment here explaining why we've had to do this,
e.g. something like "when the ServerResponseReaderThread handles a highlights
notification, it grabs the document lock before the positions lock.  To avoid a
deadlock, we must grab the locks in the same order."

[scheglov, 2015/01/28 18:33:41]

Done.

+      synchronized (positionsLock) {
+        lastText = document.get();
+        lastRegions = highlights;
+        positions = newPositions;
+      }
+    }
+  }
+
+  /**
+   * Returns the lock to use to synchronize {@link #document} access.
+   */
+  private Object getDocumentLockObject() {
+    if (document instanceof ISynchronizable) {
+      Object lock = ((ISynchronizable) document).getLockObject();
+      if (lock != null) {
+        return lock;
+      }
     }
+    return document;
   }
 
   /**