Oilpan: Introduce memory pool for CallbackStacks

third_party/WebKit/Source/platform/heap/CallbackStack.h

 // Copyright 2014 The Chromium 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 CallbackStack_h
 #define CallbackStack_h
 
 #include "platform/heap/BlinkGC.h"
 #include "wtf/Allocator.h"
 #include "wtf/Assertions.h"
+#include "wtf/Threading.h"
+#include "wtf/ThreadingPrimitives.h"
 
 namespace blink {
 
 // The CallbackStack contains all the visitor callbacks used to trace and mark
 // objects. A specific CallbackStack instance contains at most bufferSize elements.
 // If more space is needed a new CallbackStack instance is created and chained
 // together with the former instance. I.e. a logical CallbackStack can be made of
 // multiple chained CallbackStack object instances.
 class CallbackStack final {
     USING_FAST_MALLOC(CallbackStack);
 public:
     class Item {
         DISALLOW_NEW();
     public:
         Item() { }
         Item(void* object, VisitorCallback callback)
             : m_object(object)
             , m_callback(callback)
         {
         }
         void* object() { return m_object; }
         VisitorCallback callback() { return m_callback; }
         void call(Visitor* visitor) { m_callback(visitor, m_object); }
 
     private:
         void* m_object;
         VisitorCallback m_callback;
     };
 
-    explicit CallbackStack(size_t blockSize = kDefaultBlockSize);
+    static std::unique_ptr<CallbackStack> create();
     ~CallbackStack();
 
-    void clear();
+    void commit();
     void decommit();
 
     Item* allocateEntry();
     Item* pop();
 
     bool isEmpty() const;
 
     void invokeEphemeronCallbacks(Visitor*);
 
 #if ENABLE(ASSERT)
     bool hasCallbackForObject(const void*);
 #endif
+    bool hasJustOneBlock() const;
 
     static const size_t kMinimalBlockSize;
     static const size_t kDefaultBlockSize = (1 << 13);
 
 private:
     class Block {
         USING_FAST_MALLOC(Block);
     public:
-        Block(Block* next, size_t blockSize);
+        explicit Block(Block* next);
         ~Block();
 
 #if ENABLE(ASSERT)
         void clear();
 #endif
-        void reset();
-        void decommit();
-
         Block* next() const { return m_next; }
         void setNext(Block* next) { m_next = next; }
 
         bool isEmptyBlock() const
         {
             return m_current == &(m_buffer[0]);
         }
 
         size_t blockSize() const { return m_blockSize; }
 
@@ skipping 19 matching lines @@
 
     private:
         size_t m_blockSize;
 
         Item* m_buffer;
         Item* m_limit;
         Item* m_current;
         Block* m_next;
     };
 
+    CallbackStack();
     Item* popSlow();
     Item* allocateEntrySlow();
     void invokeOldestCallbacks(Block*, Block*, Visitor*);
-    bool hasJustOneBlock() const;
 
     Block* m_first;
     Block* m_last;
 };
 
+class CallbackStackMemoryPool final {
+    USING_FAST_MALLOC(CallbackStackMemoryPool);
+public:
+    // 2048 * 8 * sizeof(Item) = 256 KB (64bit) is pre-allocated for the
+    // underlying buffer of CallbackStacks.
+    static const size_t kBlockSize = 2048;
+    static const size_t kPooledBlockCount = 8;
+    static const size_t kBlockBytes = kBlockSize * sizeof(CallbackStack::Item);
+
+    static CallbackStackMemoryPool& instance();
+
+    void initialize();
+    void shutdown();
+    CallbackStack::Item* allocate();
+    void free(CallbackStack::Item*);
+
+private:
+    Mutex m_mutex;
+    int m_freeListFirst;
+    int m_freeListNext[kPooledBlockCount];
+    CallbackStack::Item* m_pooledMemory;
+};
+
 ALWAYS_INLINE CallbackStack::Item* CallbackStack::allocateEntry()
 {
+    DCHECK(m_first);
     Item* item = m_first->allocateEntry();
     if (LIKELY(!!item))
         return item;
 
     return allocateEntrySlow();
 }
 
 ALWAYS_INLINE CallbackStack::Item* CallbackStack::pop()
 {
     Item* item = m_first->pop();
     if (LIKELY(!!item))
         return item;
 
     return popSlow();
 }
 
 } // namespace blink
 
 #endif // CallbackStack_h