RingBuffer<T, N> utility with unit test; use for GC history.

runtime/vm/pages.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_PAGES_H_
 #define VM_PAGES_H_
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
+#include "vm/ring_buffer.h"
 #include "vm/spaces.h"
 #include "vm/virtual_memory.h"
 
 namespace dart {
 
 DECLARE_FLAG(bool, collect_code);
 DECLARE_FLAG(bool, log_code_drop);
 DECLARE_FLAG(bool, always_drop_code);
 
 // Forward declarations.
@@ skipping 61 matching lines @@
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(HeapPage);
 };
 
 
 // The history holds the timing information of the last garbage collection
 // runs.
 class PageSpaceGarbageCollectionHistory {
  public:
-  PageSpaceGarbageCollectionHistory();
+  PageSpaceGarbageCollectionHistory() {}
   ~PageSpaceGarbageCollectionHistory() {}
 
   void AddGarbageCollectionTime(int64_t start, int64_t end);
 
   int GarbageCollectionTimeFraction();
 
  private:
+  struct Entry {
+    int64_t start;
+    int64_t end;
+  };
   static const intptr_t kHistoryLength = 4;
-  int64_t start_[kHistoryLength];
-  int64_t end_[kHistoryLength];
-  intptr_t index_;
+  RingBuffer<Entry, kHistoryLength> history_;
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(PageSpaceGarbageCollectionHistory);
 };
 
 
 // If GC is able to reclaim more than heap_growth_ratio (in percent) memory
 // and if the relative GC time is below a given threshold,
 // then the heap is not grown when the next GC decision is made.
 // PageSpaceController controls the heap size.
@@ skipping 209 matching lines @@
   intptr_t collections_;
 
   friend class PageSpaceController;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_