Refactored PathTracer in heap.cc.

This is so that it can be reused by LOL code later.

Patch by Mark Lam from Hewlett-Packard Development Company, LP

Review URL: http://codereview.chromium.org/6541044


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6886 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -5181,32 +5181,77 @@ void HeapIterator::reset() {
 }
 
 
-#ifdef DEBUG
+#if defined(DEBUG) || defined(LIVE_OBJECT_LIST)
+
+Object* const PathTracer::kAnyGlobalObject = reinterpret_cast<Object*>(NULL);
 
-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::VisitPointers(Object** start, Object** end) {
+  bool done = ((what_to_find_ == FIND_FIRST) && found_target_);
+  // Visit all HeapObject pointers in [start, end)
+  for (Object** p = start; !done && (p < end); p++) {
+    if ((*p)->IsHeapObject()) {
+      TracePathFrom(p);
+      done = ((what_to_find_ == FIND_FIRST) && found_target_);
+    }
+  }
+}
+
+
+void PathTracer::Reset() {
+  found_target_ = false;
+  object_stack_.Clear();
+}
+
+
+void PathTracer::TracePathFrom(Object** root) {
+  ASSERT((search_target_ == kAnyGlobalObject) ||
+         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 +5260,17 @@ static void MarkObjectRecursively(Object** p) {
 
   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_target_ == kAnyGlobalObject) && obj->IsJSGlobalObject()) ||
+      (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 +5278,30 @@ static void MarkObjectRecursively(Object** p) {
 
   obj->set_map(reinterpret_cast<Map*>(map_addr + kMarkTag));
 
-  MarkObjectRecursively(&map);
+  // Scan the object body.
+  if (is_global_context && (visit_mode_ == VISIT_ONLY_STRONG)) {
+    // 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 +5320,38 @@ static void UnmarkObjectRecursively(Object** p) {
 
   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, PathTracer::FIND_ALL, VISIT_ALL);
+  IterateRoots(&tracer, VISIT_ONLY_STRONG);
 }
 
 
@@ -5337,11 +5359,10 @@ void Heap::TracePathToObject(Object* target) {
 // 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(PathTracer::kAnyGlobalObject,
+                    PathTracer::FIND_ALL,
+                    VISIT_ALL);
+  IterateRoots(&tracer, VISIT_ONLY_STRONG);
 }
 #endif
 

src/heap.h

@@ -30,6 +30,8 @@
 
 #include <math.h>
 
+#include "globals.h"
+#include "list.h"
 #include "spaces.h"
 #include "splay-tree-inl.h"
 #include "v8-counters.h"
@@ -2152,6 +2154,65 @@ class WeakObjectRetainer {
 };
 
 
+#if defined(DEBUG) || defined(LIVE_OBJECT_LIST)
+// Helper class for tracing paths to a search target Object from all roots.
+// The TracePathFrom() method can be used to trace paths from a specific
+// object to the search target object.
+class PathTracer : public ObjectVisitor {
+ public:
+  enum WhatToFind {
+    FIND_ALL,   // Will find all matches.
+    FIND_FIRST  // Will stop the search after first match.
+  };
+
+  // For the WhatToFind arg, if FIND_FIRST is specified, tracing will stop
+  // after the first match.  If FIND_ALL is specified, then tracing will be
+  // done for all matches.
+  PathTracer(Object* search_target,
+             WhatToFind what_to_find,
+             VisitMode visit_mode)
+      : search_target_(search_target),
+        found_target_(false),
+        found_target_in_trace_(false),
+        what_to_find_(what_to_find),
+        visit_mode_(visit_mode),
+        object_stack_(20),
+        no_alloc() {}
+
+  virtual void VisitPointers(Object** start, Object** end);
+
+  void Reset();
+  void TracePathFrom(Object** root);
+
+  bool found() const { return found_target_; }
+
+  static Object* const kAnyGlobalObject;
+
+ protected:
+  class MarkVisitor;
+  class UnmarkVisitor;
+
+  void MarkRecursively(Object** p, MarkVisitor* mark_visitor);
+  void UnmarkRecursively(Object** p, UnmarkVisitor* unmark_visitor);
+  virtual void ProcessResults();
+
+  // Tags 0, 1, and 3 are used. Use 2 for marking visited HeapObject.
+  static const int kMarkTag = 2;
+
+  Object* search_target_;
+  bool found_target_;
+  bool found_target_in_trace_;
+  WhatToFind what_to_find_;
+  VisitMode visit_mode_;
+  List<Object*> object_stack_;
+
+  AssertNoAllocation no_alloc;  // i.e. no gc allowed.
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
+};
+#endif  // DEBUG || LIVE_OBJECT_LIST
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_