New Heap Profiler: add API method for finding a graph node by id.

TEST=cctest/test-heap-profiler/HeapSnapshotGetNodeById

Review URL: http://codereview.chromium.org/5537001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5914 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8-profiler.h

@@ -358,6 +358,9 @@ class V8EXPORT HeapSnapshot {
   /** Returns the root node of the heap graph. */
   const HeapGraphNode* GetRoot() const;
 
+  /** Returns a node by its id. */
+  const HeapGraphNode* GetNodeById(uint64_t id) const;
+
   /**
    * Returns a diff between this snapshot and another one. Only snapshots
    * of the same type can be compared.

src/api.cc

@@ -4872,6 +4872,13 @@ const HeapGraphNode* HeapSnapshot::GetRoot() const {
 }
 
 
+const HeapGraphNode* HeapSnapshot::GetNodeById(uint64_t id) const {
+  IsDeadCheck("v8::HeapSnapshot::GetNodeById");
+  return reinterpret_cast<const HeapGraphNode*>(
+      ToInternal(this)->GetEntryById(id));
+}
+
+
 const HeapSnapshotsDiff* HeapSnapshot::CompareWith(
     const HeapSnapshot* snapshot) const {
   IsDeadCheck("v8::HeapSnapshot::CompareWith");

src/profile-generator.cc

@@ -1544,6 +1544,29 @@ HeapSnapshotsDiff* HeapSnapshot::CompareWith(HeapSnapshot* snapshot) {
 }
 
 
+HeapEntry* HeapSnapshot::GetEntryById(uint64_t id) {
+  // GetSortedEntriesList is used in diff algorithm and sorts
+  // entries by their id.
+  List<HeapEntry*>* entries_by_id = GetSortedEntriesList();
+
+  // Perform a binary search by id.
+  int low = 0;
+  int high = entries_by_id->length() - 1;
+  while (low <= high) {
+    int mid =
+        (static_cast<unsigned int>(low) + static_cast<unsigned int>(high)) >> 1;
+    uint64_t mid_id = entries_by_id->at(mid)->id();
+    if (mid_id > id)
+      high = mid - 1;
+    else if (mid_id < id)
+      low = mid + 1;
+    else
+      return entries_by_id->at(mid);
+  }
+  return NULL;
+}
+
+
 List<HeapGraphPath*>* HeapSnapshot::GetRetainingPaths(HeapEntry* entry) {
   HashMap::Entry* p =
       retaining_paths_.Lookup(entry, HeapEntry::Hash(entry), true);

src/profile-generator.h

@@ -696,6 +696,7 @@ class HeapSnapshot {
   void ApproximateRetainedSizes();
   void ClearPaint();
   HeapSnapshotsDiff* CompareWith(HeapSnapshot* snapshot);
+  HeapEntry* GetEntryById(uint64_t id);
   List<HeapGraphPath*>* GetRetainingPaths(HeapEntry* entry);
   List<HeapEntry*>* GetSortedEntriesList();
   template<class Visitor>

test/cctest/test-heap-profiler.cc

@@ -1193,4 +1193,22 @@ TEST(AggregatedHeapSnapshotJSONSerialization) {
   CHECK_EQ(1, stream.eos_signaled());
 }
 
+
+TEST(HeapSnapshotGetNodeById) {
+  v8::HandleScope scope;
+  LocalContext env;
+
+  const v8::HeapSnapshot* snapshot =
+      v8::HeapProfiler::TakeSnapshot(v8::String::New("id"));
+  const v8::HeapGraphNode* root = snapshot->GetRoot();
+  CHECK_EQ(root, snapshot->GetNodeById(root->GetId()));
+  for (int i = 0, count = root->GetChildrenCount(); i < count; ++i) {
+    const v8::HeapGraphEdge* prop = root->GetChild(i);
+    CHECK_EQ(
+        prop->GetToNode(), snapshot->GetNodeById(prop->GetToNode()->GetId()));
+  }
+  // Check a big id, which should not exist yet.
+  CHECK_EQ(NULL, snapshot->GetNodeById(0x1000000UL));
+}
+
 #endif  // ENABLE_LOGGING_AND_PROFILING