Refactored PathTracer in heap.cc....

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 6872)
+++ src/heap.cc	(working copy)
@@ -5181,32 +5181,60 @@
 }
 
 
-#ifdef DEBUG
+#if defined(DEBUG) || defined(LIVE_OBJECT_LIST)
 
-static bool search_for_any_global;
-static Object* search_target;
-static bool found_target;
-static List<Object*> object_stack(20);
+class PathTracer::MarkVisitor: public ObjectVisitor {
+ public:
+  explicit MarkVisitor(PathTracer* tracer) : tracer_(tracer) {}
+  void VisitPointers(Object** start, Object** end) {
+    // Scan all HeapObject pointers in [start, end)
+    for (Object** p = start; !tracer_->found() && (p < end); p++) {
+      if ((*p)->IsHeapObject())
+        tracer_->MarkRecursively(p, this);
+    }
+  }
 
+ private:
+  PathTracer* tracer_;
+};
 
-// Tags 0, 1, and 3 are used. Use 2 for marking visited HeapObject.
-static const int kMarkTag = 2;
 
-static void MarkObjectRecursively(Object** p);
-class MarkObjectVisitor : public ObjectVisitor {
+class PathTracer::UnmarkVisitor: public ObjectVisitor {
  public:
+  explicit UnmarkVisitor(PathTracer* tracer) : tracer_(tracer) {}
   void VisitPointers(Object** start, Object** end) {
-    // Copy all HeapObject pointers in [start, end)
+    // Scan all HeapObject pointers in [start, end)
     for (Object** p = start; p < end; p++) {
       if ((*p)->IsHeapObject())
-        MarkObjectRecursively(p);
+        tracer_->UnmarkRecursively(p, this);
     }
   }
+
+ private:
+  PathTracer* tracer_;
 };
 
-static MarkObjectVisitor mark_visitor;
 
-static void MarkObjectRecursively(Object** p) {
+void PathTracer::TracePathFrom(Object** root) {
+  if (search_for_any_global_) {
+    ASSERT(search_target_ == NULL);
+  } else {
+    ASSERT(search_target_->IsHeapObject());
+  }
+  found_target_in_trace_ = false;
+  object_stack_.Clear();
+
+  MarkVisitor mark_visitor(this);
+  MarkRecursively(root, &mark_visitor);
+
+  UnmarkVisitor unmark_visitor(this);
+  UnmarkRecursively(root, &unmark_visitor);
+
+  ProcessResults();
+}
+
+
+void PathTracer::MarkRecursively(Object** p, MarkVisitor* mark_visitor) {
   if (!(*p)->IsHeapObject()) return;
 
   HeapObject* obj = HeapObject::cast(*p);
@@ -5215,14 +5243,17 @@
 
   if (!map->IsHeapObject()) return;  // visited before
 
-  if (found_target) return;  // stop if target found
-  object_stack.Add(obj);
-  if ((search_for_any_global && obj->IsJSGlobalObject()) ||
-      (!search_for_any_global && (obj == search_target))) {
-    found_target = true;
+  if (found_target_in_trace_) return;  // stop if target found
+  object_stack_.Add(obj);
+  if ((search_for_any_global_ && obj->IsJSGlobalObject()) ||
+      (!search_for_any_global_ && (obj == search_target_))) {
+    found_target_in_trace_ = true;
+    found_target_ = true;
     return;
   }
 
+  bool is_global_context = obj->IsGlobalContext();
+
   // not visited yet
   Map* map_p = reinterpret_cast<Map*>(HeapObject::cast(map));
 
@@ -5230,31 +5261,30 @@
 
   obj->set_map(reinterpret_cast<Map*>(map_addr + kMarkTag));
 
-  MarkObjectRecursively(&map);
+  // Scan the object body.
+  if (is_global_context && skip_weak_refs_) {
+    // This is specialized to scan Context's properly.
+    Object** start = reinterpret_cast<Object**>(obj->address() +
+                                                Context::kHeaderSize);
+    Object** end = reinterpret_cast<Object**>(obj->address() +
+        Context::kHeaderSize + Context::FIRST_WEAK_SLOT * kPointerSize);
+    mark_visitor->VisitPointers(start, end);
+  } else {
+    obj->IterateBody(map_p->instance_type(),
+                     obj->SizeFromMap(map_p),
+                     mark_visitor);
+  }
 
-  obj->IterateBody(map_p->instance_type(), obj->SizeFromMap(map_p),
-                   &mark_visitor);
+  // Scan the map after the body because the body is a lot more interesting
+  // when doing leak detection.
+  MarkRecursively(&map, mark_visitor);
 
-  if (!found_target)  // don't pop if found the target
-    object_stack.RemoveLast();
+  if (!found_target_in_trace_)  // don't pop if found the target
+    object_stack_.RemoveLast();
 }
 
 
-static void UnmarkObjectRecursively(Object** p);
-class UnmarkObjectVisitor : public ObjectVisitor {
- public:
-  void VisitPointers(Object** start, Object** end) {
-    // Copy all HeapObject pointers in [start, end)
-    for (Object** p = start; p < end; p++) {
-      if ((*p)->IsHeapObject())
-        UnmarkObjectRecursively(p);
-    }
-  }
-};
-
-static UnmarkObjectVisitor unmark_visitor;
-
-static void UnmarkObjectRecursively(Object** p) {
+void PathTracer::UnmarkRecursively(Object** p, UnmarkVisitor* unmark_visitor) {
   if (!(*p)->IsHeapObject()) return;
 
   HeapObject* obj = HeapObject::cast(*p);
@@ -5273,63 +5303,38 @@
 
   obj->set_map(reinterpret_cast<Map*>(map_p));
 
-  UnmarkObjectRecursively(reinterpret_cast<Object**>(&map_p));
+  UnmarkRecursively(reinterpret_cast<Object**>(&map_p), unmark_visitor);
 
   obj->IterateBody(Map::cast(map_p)->instance_type(),
                    obj->SizeFromMap(Map::cast(map_p)),
-                   &unmark_visitor);
+                   unmark_visitor);
 }
 
 
-static void MarkRootObjectRecursively(Object** root) {
-  if (search_for_any_global) {
-    ASSERT(search_target == NULL);
-  } else {
-    ASSERT(search_target->IsHeapObject());
-  }
-  found_target = false;
-  object_stack.Clear();
-
-  MarkObjectRecursively(root);
-  UnmarkObjectRecursively(root);
-
-  if (found_target) {
+void PathTracer::ProcessResults() {
+  if (found_target_) {
     PrintF("=====================================\n");
     PrintF("====        Path to object       ====\n");
     PrintF("=====================================\n\n");
 
-    ASSERT(!object_stack.is_empty());
-    for (int i = 0; i < object_stack.length(); i++) {
+    ASSERT(!object_stack_.is_empty());
+    for (int i = 0; i < object_stack_.length(); i++) {
       if (i > 0) PrintF("\n     |\n     |\n     V\n\n");
-      Object* obj = object_stack[i];
+      Object* obj = object_stack_[i];
       obj->Print();
     }
     PrintF("=====================================\n");
   }
 }
+#endif  // DEBUG || LIVE_OBJECT_LIST
 
 
-// Helper class for visiting HeapObjects recursively.
-class MarkRootVisitor: public ObjectVisitor {
- public:
-  void VisitPointers(Object** start, Object** end) {
-    // Visit all HeapObject pointers in [start, end)
-    for (Object** p = start; p < end; p++) {
-      if ((*p)->IsHeapObject())
-        MarkRootObjectRecursively(p);
-    }
-  }
-};
-
-
+#ifdef DEBUG
 // Triggers a depth-first traversal of reachable objects from roots
 // and finds a path to a specific heap object and prints it.
 void Heap::TracePathToObject(Object* target) {
-  search_target = target;
-  search_for_any_global = false;
-
-  MarkRootVisitor root_visitor;
-  IterateRoots(&root_visitor, VISIT_ONLY_STRONG);
+  PathTracer tracer(target, false, PathTracer::FIND_ALL, false);
+  IterateRoots(&tracer, VISIT_ONLY_STRONG);
 }
 
 
@@ -5337,11 +5342,8 @@
 // and finds a path to any global object and prints it. Useful for
 // determining the source for leaks of global objects.
 void Heap::TracePathToGlobal() {
-  search_target = NULL;
-  search_for_any_global = true;
-
-  MarkRootVisitor root_visitor;
-  IterateRoots(&root_visitor, VISIT_ONLY_STRONG);
+  PathTracer tracer(NULL, true, PathTracer::FIND_ALL, false);
+  IterateRoots(&tracer, VISIT_ONLY_STRONG);
 }
 #endif