ObjectGraph: Establish a HeapIterationScope *before* making the heap writable, least the sweeper in…

runtime/vm/object_graph_test.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/assert.h"
 #include "vm/object_graph.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
@@ skipping 49 matching lines @@
   {
     // No more allocation; raw pointers ahead.
     NoSafepointScope no_safepoint_scope;
     RawObject* b_raw = b.raw();
     // Clear handles to cut unintended retained paths.
     b = Array::null();
     c = Array::null();
     d = Array::null();
     ObjectGraph graph(thread);
     {
-      // Compare count and size when 'b' is/isn't skipped.
-      CounterVisitor with(Object::null(), Object::null());
-      graph.IterateObjectsFrom(a, &with);
-      CounterVisitor without(b_raw, a.raw());
-      graph.IterateObjectsFrom(a, &without);
-      // Only 'b' and 'c' were cut off.
-      EXPECT_EQ(2, with.count() - without.count());
-      EXPECT_EQ(b_size + c_size, with.size() - without.size());
-    }
-    {
-      // Like above, but iterate over the entire isolate. The counts and sizes
-      // are thus larger, but the difference should still be just 'b' and 'c'.
-      CounterVisitor with(Object::null(), Object::null());
-      graph.IterateObjects(&with);
-      CounterVisitor without(b_raw, a.raw());
-      graph.IterateObjects(&without);
-      EXPECT_EQ(2, with.count() - without.count());
-      EXPECT_EQ(b_size + c_size, with.size() - without.size());
+      HeapIterationScope iteration_scope(true);
+      {
+        // Compare count and size when 'b' is/isn't skipped.
+        CounterVisitor with(Object::null(), Object::null());
+        graph.IterateObjectsFrom(a, &with);
+        CounterVisitor without(b_raw, a.raw());
+        graph.IterateObjectsFrom(a, &without);
+        // Only 'b' and 'c' were cut off.
+        EXPECT_EQ(2, with.count() - without.count());
+        EXPECT_EQ(b_size + c_size, with.size() - without.size());
+      }
+      {
+        // Like above, but iterate over the entire isolate. The counts and sizes
+        // are thus larger, but the difference should still be just 'b' and 'c'.
+        CounterVisitor with(Object::null(), Object::null());
+        graph.IterateObjects(&with);
+        CounterVisitor without(b_raw, a.raw());
+        graph.IterateObjects(&without);
+        EXPECT_EQ(2, with.count() - without.count());
+        EXPECT_EQ(b_size + c_size, with.size() - without.size());
+      }
     }
     EXPECT_EQ(a_size + b_size + c_size + d_size,
               graph.SizeRetainedByInstance(a));
   }
   {
     // Get hold of c again.
     b ^= a.At(10);
     c ^= b.At(0);
     b = Array::null();
     ObjectGraph graph(thread);
@@ skipping 32 matching lines @@
       Array& expected_a = Array::Handle();
       expected_a ^= path.At(4);
       EXPECT(expected_c.raw() == c.raw());
       EXPECT(expected_b.raw() == a.At(10));
       EXPECT(expected_a.raw() == a.raw());
     }
   }
 }
 
 }  // namespace dart