[heap] Move slots buffer into a separate file.

src/heap/slots-buffer.h

+// Copyright 2015 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_SLOTS_BUFFER_H_
+#define V8_SLOTS_BUFFER_H_
+
+#include "src/objects.h"
+
+namespace v8 {
+namespace internal {
+
+// Forward declarations.
+class SlotsBuffer;
+
+
+class SlotsBufferAllocator {
+ public:
+  SlotsBuffer* AllocateBuffer(SlotsBuffer* next_buffer);
+  void DeallocateBuffer(SlotsBuffer* buffer);
+
+  void DeallocateChain(SlotsBuffer** buffer_address);
+};
+
+
+// SlotsBuffer records a sequence of slots that has to be updated
+// after live objects were relocated from evacuation candidates.
+// All slots are either untyped or typed:
+//    - Untyped slots are expected to contain a tagged object pointer.
+//      They are recorded by an address.
+//    - Typed slots are expected to contain an encoded pointer to a heap
+//      object where the way of encoding depends on the type of the slot.
+//      They are recorded as a pair (SlotType, slot address).
+// We assume that zero-page is never mapped this allows us to distinguish
+// untyped slots from typed slots during iteration by a simple comparison:
+// if element of slots buffer is less than NUMBER_OF_SLOT_TYPES then it
+// is the first element of typed slot's pair.
+class SlotsBuffer {
+ public:
+  typedef Object** ObjectSlot;
+
+  explicit SlotsBuffer(SlotsBuffer* next_buffer)
+      : idx_(0), chain_length_(1), next_(next_buffer) {
+    if (next_ != NULL) {
+      chain_length_ = next_->chain_length_ + 1;
+    }
+  }
+
+  ~SlotsBuffer() {}
+
+  void Add(ObjectSlot slot) {
+    DCHECK(0 <= idx_ && idx_ < kNumberOfElements);
+#ifdef DEBUG
+    if (slot >= reinterpret_cast<ObjectSlot>(NUMBER_OF_SLOT_TYPES)) {
+      DCHECK_NOT_NULL(*slot);
+    }
+#endif
+    slots_[idx_++] = slot;
+  }
+
+  ObjectSlot Get(intptr_t i) {
+    DCHECK(i >= 0 && i < kNumberOfElements);
+    return slots_[i];
+  }
+
+  size_t Size() {
+    DCHECK(idx_ <= kNumberOfElements);
+    return idx_;
+  }
+
+  enum SlotType {
+    EMBEDDED_OBJECT_SLOT,
+    OBJECT_SLOT,
+    RELOCATED_CODE_OBJECT,
+    CELL_TARGET_SLOT,
+    CODE_TARGET_SLOT,
+    CODE_ENTRY_SLOT,
+    DEBUG_TARGET_SLOT,
+    NUMBER_OF_SLOT_TYPES
+  };
+
+  static const char* SlotTypeToString(SlotType type) {
+    switch (type) {
+      case EMBEDDED_OBJECT_SLOT:
+        return "EMBEDDED_OBJECT_SLOT";
+      case OBJECT_SLOT:
+        return "OBJECT_SLOT";
+      case RELOCATED_CODE_OBJECT:
+        return "RELOCATED_CODE_OBJECT";
+      case CELL_TARGET_SLOT:
+        return "CELL_TARGET_SLOT";
+      case CODE_TARGET_SLOT:
+        return "CODE_TARGET_SLOT";
+      case CODE_ENTRY_SLOT:
+        return "CODE_ENTRY_SLOT";
+      case DEBUG_TARGET_SLOT:
+        return "DEBUG_TARGET_SLOT";
+      case NUMBER_OF_SLOT_TYPES:
+        return "NUMBER_OF_SLOT_TYPES";
+    }
+    return "UNKNOWN SlotType";
+  }
+
+  SlotsBuffer* next() { return next_; }
+
+  static int SizeOfChain(SlotsBuffer* buffer) {
+    if (buffer == NULL) return 0;
+    return static_cast<int>(buffer->idx_ +
+                            (buffer->chain_length_ - 1) * kNumberOfElements);
+  }
+
+  inline bool IsFull() { return idx_ == kNumberOfElements; }
+
+  inline bool HasSpaceForTypedSlot() { return idx_ < kNumberOfElements - 1; }
+
+  enum AdditionMode { FAIL_ON_OVERFLOW, IGNORE_OVERFLOW };
+
+  static bool ChainLengthThresholdReached(SlotsBuffer* buffer) {
+    return buffer != NULL && buffer->chain_length_ >= kChainLengthThreshold;
+  }
+
+  INLINE(static bool AddToSynchronized(SlotsBufferAllocator* allocator,
+                                       SlotsBuffer** buffer_address,
+                                       base::Mutex* buffer_mutex,
+                                       ObjectSlot slot, AdditionMode mode)) {
+    base::LockGuard<base::Mutex> lock_guard(buffer_mutex);
+    return AddTo(allocator, buffer_address, slot, mode);
+  }
+
+  INLINE(static bool AddTo(SlotsBufferAllocator* allocator,
+                           SlotsBuffer** buffer_address, ObjectSlot slot,
+                           AdditionMode mode)) {
+    SlotsBuffer* buffer = *buffer_address;
+    if (buffer == NULL || buffer->IsFull()) {
+      if (mode == FAIL_ON_OVERFLOW && ChainLengthThresholdReached(buffer)) {
+        allocator->DeallocateChain(buffer_address);
+        return false;
+      }
+      buffer = allocator->AllocateBuffer(buffer);
+      *buffer_address = buffer;
+    }
+    buffer->Add(slot);
+    return true;
+  }
+
+  static bool IsTypedSlot(ObjectSlot slot);
+
+  static bool AddToSynchronized(SlotsBufferAllocator* allocator,
+                                SlotsBuffer** buffer_address,
+                                base::Mutex* buffer_mutex, SlotType type,
+                                Address addr, AdditionMode mode);
+
+  static bool AddTo(SlotsBufferAllocator* allocator,
+                    SlotsBuffer** buffer_address, SlotType type, Address addr,
+                    AdditionMode mode);
+
+  // Eliminates all stale entries from the slots buffer, i.e., slots that
+  // are not part of live objects anymore. This method must be called after
+  // marking, when the whole transitive closure is known and must be called
+  // before sweeping when mark bits are still intact.
+  static void RemoveInvalidSlots(Heap* heap, SlotsBuffer* buffer);
+
+  // Eliminate all slots that are within the given address range.
+  static void RemoveObjectSlots(Heap* heap, SlotsBuffer* buffer,
+                                Address start_slot, Address end_slot);
+
+  // Ensures that there are no invalid slots in the chain of slots buffers.
+  static void VerifySlots(Heap* heap, SlotsBuffer* buffer);
+
+  static const int kNumberOfElements = 1021;
+
+ private:
+  static const int kChainLengthThreshold = 15;
+
+  intptr_t idx_;
+  intptr_t chain_length_;
+  SlotsBuffer* next_;
+  ObjectSlot slots_[kNumberOfElements];
+};
+
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_SLOTS_BUFFER_H_