[profiler] Implement POC Sampling Heap Profiler

src/heap/spaces.h

 // Copyright 2011 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_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include "src/allocation.h"
 #include "src/atomic-utils.h"
 #include "src/base/atomicops.h"
@@ skipping 2559 matching lines @@
 // -----------------------------------------------------------------------------
 // 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() {}
 
- private:
+  // 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;
 
-  // 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);
-      bytes_to_next_step_ = step_size_;
-    }
-  }
+  // 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);
 };
 
 // -----------------------------------------------------------------------------
 // The young generation space.
 //
 // The new space consists of a contiguous pair of semispaces.  It simply
 // forwards most functions to the appropriate semispace.
 
 class NewSpace : public Space {
@@ skipping 594 matching lines @@
     count = 0;
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SPACES_H_