[profiler] Implement POC Sampling Heap Profiler

src/profiler/sampling-heap-profiler.h

+// 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.
+
+#ifndef V8_PROFILER_SAMPLING_HEAP_PROFILER_H_
+#define V8_PROFILER_SAMPLING_HEAP_PROFILER_H_
+
+#include <set>
+#include "src/base/utils/random-number-generator.h"
+#include "src/profiler/allocation-tracker.h"
+
+namespace v8 {
+namespace internal {
+
+class SamplingHeapProfiler : public InlineAllocationObserver {
+ public:
+  SamplingHeapProfiler(Heap* heap, StringsStorage* names, uint64_t rate,
+                       int stack_depth);
+  ~SamplingHeapProfiler();
+
+  void GetHeapSample(OutputStream* stream);
+
+  void Step(int bytes_allocated, Address soon_object, size_t size) override;
+  intptr_t GetNextStepSize() override {
+    return GetNextSampleInterval(random_, rate_);
+  }
+
+  StringsStorage* names() const { return names_; }
+
+  struct FunctionInfo {
+    FunctionInfo(SharedFunctionInfo* shared, StringsStorage* names);
+
+    const char* const name;
+    const char* script_name;
+    int script_id;
+    int start_position;
+  };
+
+  class SampledAllocation {
+   public:
+    SampledAllocation(SamplingHeapProfiler* shp, Isolate* isolate,
+                      Local<Value> local, size_t size, int max_frames);
+    ~SampledAllocation() {
+      stack_.Iterate(&DeleteFunctionInfo);
+      global_.Reset();  // drop the reference.
+    }
+    size_t get_size() const { return size_; }
+    List<FunctionInfo*>& get_stack() { return stack_; }
+
+   private:
+    static void OnWeakCallback(const WeakCallbackInfo<SampledAllocation>& data);
+    static void DeleteFunctionInfo(FunctionInfo** infop) { delete *infop; }
+
+    SamplingHeapProfiler* const shp_;
+    Global<Value> global_;
+    List<FunctionInfo*> stack_;
+    const size_t size_;
+
+    DISALLOW_COPY_AND_ASSIGN(SampledAllocation);
+  };
+
+ private:
+  Heap* heap() const { return heap_; }
+
+  void SampleObject(Address soon_object, size_t size);
+
+  static intptr_t GetNextSampleInterval(base::RandomNumberGenerator* random,
+                                        uint64_t rate);
+
+  Isolate* const isolate_;
+  Heap* const heap_;
+  base::RandomNumberGenerator* const random_;
+  StringsStorage* const names_;
+  std::set<SampledAllocation*> samples_;
+  const uint64_t rate_;
+  const int stack_depth_;
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_PROFILER_SAMPLING_HEAP_PROFILER_H_