Oilpan: Introduce memory pool for CallbackStacks

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

Index: third_party/WebKit/Source/platform/heap/CallbackStack.h
diff --git a/third_party/WebKit/Source/platform/heap/CallbackStack.h b/third_party/WebKit/Source/platform/heap/CallbackStack.h
index 97fe8280fb357a70a77daa5f07fe4929bc74cded..5b835800750a7e4039e05615535319deb02baf95 100644
--- a/third_party/WebKit/Source/platform/heap/CallbackStack.h
+++ b/third_party/WebKit/Source/platform/heap/CallbackStack.h
@@ -8,6 +8,8 @@
 #include "platform/heap/BlinkGC.h"
 #include "wtf/Allocator.h"
 #include "wtf/Assertions.h"
+#include "wtf/Threading.h"
+#include "wtf/ThreadingPrimitives.h"
 
 namespace blink {
 
@@ -37,10 +39,10 @@ public:
         VisitorCallback m_callback;
     };
 
-    explicit CallbackStack(size_t blockSize = kDefaultBlockSize);
+    static std::unique_ptr<CallbackStack> create();
     ~CallbackStack();
 
-    void clear();
+    void commit();
     void decommit();
 
     Item* allocateEntry();
@@ -53,6 +55,7 @@ public:
 #if ENABLE(ASSERT)
     bool hasCallbackForObject(const void*);
 #endif
+    bool hasJustOneBlock() const;
 
     static const size_t kMinimalBlockSize;
     static const size_t kDefaultBlockSize = (1 << 13);
@@ -61,15 +64,12 @@ 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; }
 
@@ -109,17 +109,41 @@ private:
         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;