Object graph visitor: general depth-first search.

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 {
+
+class Counter : public ObjectGraph::Visitor {
+ public:
+  // Records the number of objects and total size visited, excluding 'skip'
+  // and any objects only reachable through 'skip'.
+  Counter(RawObject* skip, RawObject* expected_parent)
+      : count_(0), size_(0), skip_(skip), expected_parent_(expected_parent) { }
+
+  virtual Direction VisitObject(ObjectGraph::StackIterator* it) {
+    RawObject* obj = it->Get();
+    if (obj == skip_) {
+      EXPECT(it->MoveToParent());
+      EXPECT_EQ(expected_parent_, it->Get());
+      return kBacktrack;
+    }
+    ++count_;
+    size_ += obj->Size();
+    return kProceed;
+  }
+
+  int count() const { return count_; }
+  int size() const { return size_; }
+
+ private:
+  int count_;
+  intptr_t size_;
+  RawObject* skip_;
+  RawObject* expected_parent_;
+};
+
+
+TEST_CASE(ObjectGraph) {
+  Isolate* isolate = Isolate::Current();
+  // Create a simple object graph with objects a, b, c, d:
+  //  a+->b+->c
+  //  +   +
+  //  |   v
+  //  +-->d
+  Array& a = Array::Handle(Array::New(2, Heap::kNew));
+  Array& b = Array::Handle(Array::New(2, Heap::kOld));
+  Array& c = Array::Handle(Array::New(0, Heap::kOld));
+  Array& d = Array::Handle(Array::New(0, Heap::kOld));
+  a.SetAt(0, b);
+  b.SetAt(0, c);
+  b.SetAt(1, d);
+  a.SetAt(1, d);
+  intptr_t b_size = b.raw()->Size();
+  intptr_t c_size = c.raw()->Size();
+  {
+    // No more allocation; raw pointers ahead.
+    NoGCScope no_gc_scope;
+    RawObject* b_raw = b.raw();
+    // Clear handles to cut unintended retained paths.
+    b = Array::null();
+    c = Array::null();
+    d = Array::null();
+    ObjectGraph graph(isolate);
+    {
+      // Compare count and size when 'b' is/isn't skipped.
+      Counter with(Object::null(), Object::null());
+      graph.IterateObjectsFrom(a, &with);
+      Counter 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'.
+      Counter with(Object::null(), Object::null());
+      graph.IterateObjects(&with);
+      Counter 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());
+    }
+  }
+}
+
+}  // namespace dart