[Truffle] Shared Objects: add a couple explanations for the Shape re-…

…check.
jruby · Nov 21, 2016 · 1a8a43a · 1a8a43a
1 parent acad490
commit 1a8a43a
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/truffle/src/main/java/org/jruby/truffle/language/objects/WriteObjectFieldNode.java b/truffle/src/main/java/org/jruby/truffle/language/objects/WriteObjectFieldNode.java
@@ -60,6 +60,9 @@ public void writeExistingField(DynamicObject object, Object value,
             if (shared) {
                 writeBarrierNode.executeWriteBarrier(value);
                 synchronized (object) {
+                    // Re-check the shape under the monitor as another thread might have changed it
+                    // by adding a field (fine) or upgrading an existing field to Object storage
+                    // (need to use the new storage)
                     if (object.getShape() != cachedShape) {
                         CompilerDirectives.transferToInterpreter();
                         execute(object, value);
@@ -95,6 +98,9 @@ public void writeNewField(DynamicObject object, Object value,
             if (shared) {
                 writeBarrierNode.executeWriteBarrier(value);
                 synchronized (object) {
+                    // Re-check the shape under the monitor as another thread might have changed it
+                    // by adding a field or upgrading an existing field to Object storage
+                    // (we need to make sure to have the right shape to add the new field)
                     if (object.getShape() != oldShape) {
                         CompilerDirectives.transferToInterpreter();
                         execute(object, value);