[profiler] Implement POC Sampling Heap Profiler

src/profiler/heap-profiler.h

Index: src/profiler/heap-profiler.h
diff --git a/src/profiler/heap-profiler.h b/src/profiler/heap-profiler.h
index 9a04e83af4b0ca2f3725f8a10fcdabd322ba41b7..f43832c68cb05704744cfdc43810c50de9533f6e 100644
--- a/src/profiler/heap-profiler.h
+++ b/src/profiler/heap-profiler.h
@@ -5,6 +5,7 @@
 #ifndef V8_PROFILER_HEAP_PROFILER_H_
 #define V8_PROFILER_HEAP_PROFILER_H_
 
+#include "include/v8-util.h"
 #include "src/base/smart-pointers.h"
 #include "src/isolate.h"
 #include "src/list.h"
@@ -16,6 +17,7 @@ namespace internal {
 class AllocationTracker;
 class HeapObjectsMap;
 class HeapSnapshot;
+class SamplingHeapProfiler;
 class StringsStorage;
 
 class HeapProfiler {
@@ -29,6 +31,10 @@ class HeapProfiler {
       v8::ActivityControl* control,
       v8::HeapProfiler::ObjectNameResolver* resolver);
 
+  bool StartSamplingHeapProfiler(uint64_t sample_interval, int stack_depth);
+  void StopSamplingHeapProfiler();
+  void GetHeapSample(OutputStream* stream);
+
   void StartHeapObjectsTracking(bool track_allocations);
   void StopHeapObjectsTracking();
   AllocationTracker* allocation_tracker() const {
@@ -79,6 +85,103 @@ class HeapProfiler {
   base::SmartPointer<AllocationTracker> allocation_tracker_;
   bool is_tracking_object_moves_;
   base::Mutex profiler_mutex_;
+  base::SmartPointer<SamplingHeapProfiler> sampling_heap_profiler_;
+};
+
+template <int bytes>
+struct MaxDecimalDigitsIn;
+template <>
+struct MaxDecimalDigitsIn<4> {
+  static const int kSigned = 11;
+  static const int kUnsigned = 10;
+};
+template <>
+struct MaxDecimalDigitsIn<8> {
+  static const int kSigned = 20;
+  static const int kUnsigned = 20;
+};
+
+class OutputStreamWriter {
+ public:
+  explicit OutputStreamWriter(v8::OutputStream* stream)
+      : stream_(stream),
+        chunk_size_(stream->GetChunkSize()),
+        chunk_(chunk_size_),
+        chunk_pos_(0),
+        aborted_(false) {
+    DCHECK(chunk_size_ > 0);
+  }
+  bool aborted() { return aborted_; }
+  void AddCharacter(char c) {
+    DCHECK(c != '\0');
+    DCHECK(chunk_pos_ < chunk_size_);
+    chunk_[chunk_pos_++] = c;
+    MaybeWriteChunk();
+  }
+  void AddString(const char* s) { AddSubstring(s, StrLength(s)); }
+  void AddSubstring(const char* s, int n) {
+    if (n <= 0) return;
+    DCHECK(static_cast<size_t>(n) <= strlen(s));
+    const char* s_end = s + n;
+    while (s < s_end) {
+      int s_chunk_size =
+          Min(chunk_size_ - chunk_pos_, static_cast<int>(s_end - s));
+      DCHECK(s_chunk_size > 0);
+      MemCopy(chunk_.start() + chunk_pos_, s, s_chunk_size);
+      s += s_chunk_size;
+      chunk_pos_ += s_chunk_size;
+      MaybeWriteChunk();
+    }
+  }
+  void AddNumber(unsigned n) { AddNumberImpl<unsigned>(n, "%u"); }
+  void Finalize() {
+    if (aborted_) return;
+    DCHECK(chunk_pos_ < chunk_size_);
+    if (chunk_pos_ != 0) {
+      WriteChunk();
+    }
+    stream_->EndOfStream();
+  }
+
+ private:
+  template <typename T>
+  void AddNumberImpl(T n, const char* format) {
+    // Buffer for the longest value plus trailing \0
+    static const int kMaxNumberSize =
+        MaxDecimalDigitsIn<sizeof(T)>::kUnsigned + 1;
+    if (chunk_size_ - chunk_pos_ >= kMaxNumberSize) {
+      int result =
+          SNPrintF(chunk_.SubVector(chunk_pos_, chunk_size_), format, n);
+      DCHECK(result != -1);
+      chunk_pos_ += result;
+      MaybeWriteChunk();
+    } else {
+      EmbeddedVector<char, kMaxNumberSize> buffer;
+      int result = SNPrintF(buffer, format, n);
+      USE(result);
+      DCHECK(result != -1);
+      AddString(buffer.start());
+    }
+  }
+  void MaybeWriteChunk() {
+    DCHECK(chunk_pos_ <= chunk_size_);
+    if (chunk_pos_ == chunk_size_) {
+      WriteChunk();
+    }
+  }
+  void WriteChunk() {
+    if (aborted_) return;
+    if (stream_->WriteAsciiChunk(chunk_.start(), chunk_pos_) ==
+        v8::OutputStream::kAbort)
+      aborted_ = true;
+    chunk_pos_ = 0;
+  }
+
+  v8::OutputStream* stream_;
+  int chunk_size_;
+  ScopedVector<char> chunk_;
+  int chunk_pos_;
+  bool aborted_;
 };
 
 }  // namespace internal