[profiler] Implement POC Sampling Heap Profiler

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 549dfdd440501da2929cd7940538aa8084d12b60..4a8a9bb1f6ae03257ebe66c091fcc7658d1c183b 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -470,6 +470,7 @@ class GCTracer;
 class HeapObjectsFilter;
 class HeapStats;
 class HistogramTimer;
+class InlineAllocationObserver;
 class Isolate;
 class MemoryReducer;
 class ObjectStats;
@@ -2755,6 +2756,60 @@ class PathTracer : public ObjectVisitor {
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
+
+// -----------------------------------------------------------------------------
+// Allows observation of inline allocation in the new space.
+class InlineAllocationObserver {
+ public:
+  explicit InlineAllocationObserver(intptr_t step_size)
+      : step_size_(step_size), bytes_to_next_step_(step_size) {
+    DCHECK(step_size >= kPointerSize);
+  }
+  virtual ~InlineAllocationObserver() {}
+
+  // Called each time the new space does an inline allocation step. This may be
+  // more frequently than the step_size we are monitoring (e.g. when there are
+  // multiple observers, or when page or space boundary is encountered.)
+  void InlineAllocationStep(int bytes_allocated, Address soon_object,
+                            size_t size) {
+    bytes_to_next_step_ -= bytes_allocated;
+    if (bytes_to_next_step_ <= 0) {
+      Step(static_cast<int>(step_size_ - bytes_to_next_step_), soon_object,
+           size);
+      step_size_ = GetNextStepSize();
+      bytes_to_next_step_ = step_size_;
+    }
+  }
+
+ protected:
+  intptr_t step_size() const { return step_size_; }
+  intptr_t bytes_to_next_step() const { return bytes_to_next_step_; }
+
+  // Pure virtual method provided by the subclasses that gets called when at
+  // least step_size bytes have been allocated. soon_object is the address just
+  // allocated (but not yet initialized.) size is the size of the object as
+  // requested (i.e. w/o the alignment fillers). Some complexities to be aware
+  // of:
+  // 1) soon_object will be nullptr in cases where we end up observing an
+  //    allocation that happens to be a filler space (e.g. page boundaries.)
+  // 2) size is the requested size at the time of allocation. Right-trimming
+  //    may change the object size dynamically.
+  // 3) soon_object may actually be the first object in an allocation-folding
+  //    group. In such a case size is the size of the group rather than the
+  //    first object.
+  virtual void Step(int bytes_allocated, Address soon_object, size_t size) = 0;
+
+  // Subclasses can override this method to make step size dynamic.
+  virtual intptr_t GetNextStepSize() { return step_size_; }
+
+  intptr_t step_size_;
+  intptr_t bytes_to_next_step_;
+
+ private:
+  friend class NewSpace;
+  DISALLOW_COPY_AND_ASSIGN(InlineAllocationObserver);
+};
+
 }  // namespace internal
 }  // namespace v8