Sampling heap profiler: remove empty nodes from profile.

src/profiler/sampling-heap-profiler.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/profiler/sampling-heap-profiler.h"
 
 #include <stdint.h>
 #include <memory>
 #include "src/api.h"
 #include "src/base/utils/random-number-generator.h"
@@ skipping 40 matching lines @@
                                            uint64_t rate, int stack_depth)
     : isolate_(heap->isolate()),
       heap_(heap),
       new_space_observer_(new SamplingAllocationObserver(
           heap_, static_cast<intptr_t>(rate), rate, this,
           heap->isolate()->random_number_generator())),
       other_spaces_observer_(new SamplingAllocationObserver(
           heap_, static_cast<intptr_t>(rate), rate, this,
           heap->isolate()->random_number_generator())),
       names_(names),
-      profile_root_("(root)", v8::UnboundScript::kNoScriptId, 0),
+      profile_root_(nullptr, "(root)", v8::UnboundScript::kNoScriptId, 0),
       samples_(),
       stack_depth_(stack_depth),
       rate_(rate) {
   CHECK_GT(rate_, 0);
   heap->new_space()->AddAllocationObserver(new_space_observer_.get());
   AllSpaces spaces(heap);
-  for (Space* space = spaces.next(); space != NULL; space = spaces.next()) {
+  for (Space* space = spaces.next(); space != nullptr; space = spaces.next()) {
     if (space != heap->new_space()) {
       space->AddAllocationObserver(other_spaces_observer_.get());
     }
   }
 }
 
 
 SamplingHeapProfiler::~SamplingHeapProfiler() {
   heap_->new_space()->RemoveAllocationObserver(new_space_observer_.get());
   AllSpaces spaces(heap_);
-  for (Space* space = spaces.next(); space != NULL; space = spaces.next()) {
+  for (Space* space = spaces.next(); space != nullptr; space = spaces.next()) {
     if (space != heap_->new_space()) {
       space->RemoveAllocationObserver(other_spaces_observer_.get());
     }
   }
 
   for (auto sample : samples_) {
     delete sample;
   }
   std::set<Sample*> empty;
   samples_.swap(empty);
@@ skipping 22 matching lines @@
 }
 
 void SamplingHeapProfiler::OnWeakCallback(
     const WeakCallbackInfo<Sample>& data) {
   Sample* sample = data.GetParameter();
   AllocationNode* node = sample->owner;
   DCHECK(node->allocations_[sample->size] > 0);
   node->allocations_[sample->size]--;
   if (node->allocations_[sample->size] == 0) {
     node->allocations_.erase(sample->size);
+    while (node->allocations_.empty() && node->children_.empty() &&
+           node->parent_ && !node->parent_->pinned_) {
+      AllocationNode* parent = node->parent_;
+      parent->children_.erase(
+          std::find(parent->children_.begin(), parent->children_.end(), node));
+      delete node;
+      node = parent;
+    }
   }
   sample->profiler->samples_.erase(sample);
   delete sample;
 }
 
 SamplingHeapProfiler::AllocationNode* SamplingHeapProfiler::FindOrAddChildNode(
     AllocationNode* parent, const char* name, int script_id,
     int start_position) {
   for (AllocationNode* child : parent->children_) {
     if (child->script_id_ == script_id &&
         child->script_position_ == start_position &&
         strcmp(child->name_, name) == 0) {
       return child;
     }
   }
-  AllocationNode* child = new AllocationNode(name, script_id, start_position);
+  AllocationNode* child =
+      new AllocationNode(parent, name, script_id, start_position);
   parent->children_.push_back(child);
   return child;
 }
 
 SamplingHeapProfiler::AllocationNode* SamplingHeapProfiler::AddStack() {
   AllocationNode* node = &profile_root_;
 
   std::vector<SharedFunctionInfo*> stack;
   StackTraceFrameIterator it(isolate_);
   int frames_captured = 0;
@@ skipping 42 matching lines @@
       script_id = script->id();
     }
     node = FindOrAddChildNode(node, name, script_id, shared->start_position());
   }
   return node;
 }
 
 v8::AllocationProfile::Node* SamplingHeapProfiler::TranslateAllocationNode(
     AllocationProfile* profile, SamplingHeapProfiler::AllocationNode* node,
     const std::map<int, Handle<Script>>& scripts) {
+  // By pinning the node we make sure its children won't get disposed if
+  // a GC kicks in during the tree retrieval.
+  node->pinned_ = true;
   Local<v8::String> script_name =
       ToApiHandle<v8::String>(isolate_->factory()->InternalizeUtf8String(""));
   int line = v8::AllocationProfile::kNoLineNumberInfo;
   int column = v8::AllocationProfile::kNoColumnNumberInfo;
   std::vector<v8::AllocationProfile::Allocation> allocations;
   allocations.reserve(node->allocations_.size());
   if (node->script_id_ != v8::UnboundScript::kNoScriptId &&
       scripts.find(node->script_id_) != scripts.end()) {
     // Cannot use std::map<T>::at because it is not available on android.
     auto non_const_scripts =
@@ skipping 22 matching lines @@
   size_t child_len = node->children_.size();
   // The children vector may have nodes appended to it during translation
   // because the translation may allocate strings on the JS heap that have
   // the potential to be sampled. We cache the length of the vector before
   // iteration so that nodes appended to the vector during iteration are
   // not processed.
   for (size_t i = 0; i < child_len; i++) {
     current->children.push_back(
         TranslateAllocationNode(profile, node->children_[i], scripts));
   }
+  node->pinned_ = false;
   return current;
 }
 
 v8::AllocationProfile* SamplingHeapProfiler::GetAllocationProfile() {
   // To resolve positions to line/column numbers, we will need to look up
   // scripts. Build a map to allow fast mapping from script id to script.
   std::map<int, Handle<Script>> scripts;
   {
     Script::Iterator iterator(isolate_);
     while (Script* script = iterator.Next()) {
       scripts[script->id()] = handle(script);
     }
   }
   auto profile = new v8::internal::AllocationProfile();
   TranslateAllocationNode(profile, &profile_root_, scripts);
   return profile;
 }
 
 
 }  // namespace internal
 }  // namespace v8