Thread-local store buffers, v2

runtime/vm/store_buffer.h

 // Copyright (c) 2012, 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_STORE_BUFFER_H_
 #define VM_STORE_BUFFER_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 
 namespace dart {
 
 // Forward declarations.
 class Isolate;
+class Mutex;
 class RawObject;
 
 class StoreBufferBlock {
  public:
-  // Each block contains kSize pointers.
+  // Each full block contains kSize pointers.
   static const int32_t kSize = 1024;
 
-  explicit StoreBufferBlock(StoreBufferBlock* next) : next_(next), top_(0) {}
-
   void Reset() { top_ = 0; }
 
+  // TODO(koda): Make private after adding visitor interface to StoreBuffer.
   StoreBufferBlock* next() const { return next_; }
 
   intptr_t Count() const { return top_; }
+  bool IsFull() const { return Count() == kSize; }
+
+  void Add(RawObject* obj) {
+    ASSERT(!IsFull());
+    pointers_[top_++] = obj;
+  }
 
   RawObject* At(intptr_t i) const {
     ASSERT(i >= 0);
     ASSERT(i < top_);
     return pointers_[i];
   }
 
+#if defined(TESTING)
+  bool Contains(RawObject* obj) const {
+    for (intptr_t i = 0; i < Count(); i++) {
+      if (At(i) == obj) {
+        return true;
+      }
+    }
+    return false;
+  }
+#endif  // TESTING
+
   static intptr_t top_offset() { return OFFSET_OF(StoreBufferBlock, top_); }
   static intptr_t pointers_offset() {
     return OFFSET_OF(StoreBufferBlock, pointers_);
   }
 
  private:
+  StoreBufferBlock() : next_(NULL), top_(0) {}
+
   StoreBufferBlock* next_;
   int32_t top_;
   RawObject* pointers_[kSize];
 
   friend class StoreBuffer;
 
   DISALLOW_COPY_AND_ASSIGN(StoreBufferBlock);
 };
 
 
 class StoreBuffer {
  public:
-  StoreBuffer() : blocks_(new StoreBufferBlock(NULL)), full_count_(0) {}
-  explicit StoreBuffer(bool shallow_copy) : blocks_(NULL), full_count_(0) {
-    // The value shallow_copy is only used to select this non-allocating
-    // constructor. It is always expected to be true.
-    ASSERT(shallow_copy);
-  }
+  StoreBuffer();
   ~StoreBuffer();
 
-  intptr_t Count() const {
-    return blocks_->Count() + (full_count_ * StoreBufferBlock::kSize);
-  }
+  // Adds and transfers ownership of the block to the buffer.
+  void PushBlock(StoreBufferBlock* block, bool check_threshold = true);
+  // Partially filled blocks can be reused, and there is an "inifite" supply
+  // of empty blocks (reused or newly allocated). In any case, the caller
+  // takes ownership of the returned block.
+  StoreBufferBlock* PopBlock();
+  StoreBufferBlock* PopEmptyBlock();
 
+  // Pops and returns all non-empty blocks as a linked list (owned by caller).
+  // TODO(koda): Replace with VisitObjectPointers.
+  StoreBufferBlock* Blocks();
+
+  // Discards the contents of this store buffer.
   void Reset();
 
-  void AddObject(RawObject* obj) {
-    StoreBufferBlock* block = blocks_;
-    ASSERT(block->top_ < StoreBufferBlock::kSize);
-    block->pointers_[block->top_++] = obj;
-    if (block->top_ == StoreBufferBlock::kSize) {
-      Expand(true);
-    }
-  }
+ private:
+  class List {
+   public:
+    List() : head_(NULL), length_(0) {}
+    ~List();
+    void Push(StoreBufferBlock* block);
+    StoreBufferBlock* Pop();
+    intptr_t length() const { return length_; }
+    bool IsEmpty() const { return head_ == NULL; }
+    StoreBufferBlock* PopAll();
+   private:
+    StoreBufferBlock* head_;
+    intptr_t length_;
+    DISALLOW_COPY_AND_ASSIGN(List);
+  };
 
-  void AddObjectGC(RawObject* obj) {
-    StoreBufferBlock* block = blocks_;
-    ASSERT(block->top_ < StoreBufferBlock::kSize);
-    block->pointers_[block->top_++] = obj;
-    if (block->top_ == StoreBufferBlock::kSize) {
-      Expand(false);
-    }
-  }
-
-  StoreBufferBlock* Blocks() {
-    StoreBufferBlock* result = blocks_;
-    blocks_ = new StoreBufferBlock(NULL);
-    full_count_ = 0;
-    return result;
-  }
-
-  // Expand the storage and optionally check whethe to schedule an interrupt.
-  void Expand(bool check);
-
-  bool Contains(RawObject* raw);
-
-  static int blocks_offset() { return OFFSET_OF(StoreBuffer, blocks_); }
-
- private:
   // Check if we run over the max number of deduplication sets.
   // If we did schedule an interrupt.
   void CheckThreshold();
 
-  StoreBufferBlock* blocks_;
-  intptr_t full_count_;
+  List full_;
+  List partial_;
+  // TODO(koda): static List empty_
+  Mutex* mutex_;
 
   DISALLOW_COPY_AND_ASSIGN(StoreBuffer);
 };
 
 }  // namespace dart
 
 #endif  // VM_STORE_BUFFER_H_