Revert of Support impl-side painting in Mandoline.

components/html_viewer/discardable_memory_allocator.cc

 // Copyright 2015 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.
 
 #include "components/html_viewer/discardable_memory_allocator.h"
 
 #include "base/memory/discardable_memory.h"
+#include "base/memory/weak_ptr.h"
 #include "base/stl_util.h"
 
 namespace html_viewer {
 
-// Interface to the rest of the program. These objects are owned outside of the
-// allocator.
-class DiscardableMemoryAllocator::DiscardableMemoryChunkImpl
-    : public base::DiscardableMemory {
+// Represents an actual memory chunk. This is an object owned by
+// DiscardableMemoryAllocator. DiscardableMemoryChunkImpl are passed to the
+// rest of the program, and access this memory through a weak ptr.
+class DiscardableMemoryAllocator::OwnedMemoryChunk {
  public:
-  DiscardableMemoryChunkImpl(size_t size, DiscardableMemoryAllocator* allocator)
+  OwnedMemoryChunk(size_t size, DiscardableMemoryAllocator* allocator)
       : is_locked_(true),
         size_(size),
         data_(new uint8_t[size]),
-        allocator_(allocator) {}
+        allocator_(allocator),
+        weak_factory_(this) {}
+  ~OwnedMemoryChunk() {}
 
-  ~DiscardableMemoryChunkImpl() override {
-    // Either the memory is discarded or the memory chunk is unlocked.
-    DCHECK(data_ || !is_locked_);
-    if (!is_locked_ && data_)
-      allocator_->NotifyDestructed(unlocked_position_);
+  void Lock() {
+    DCHECK(!is_locked_);
+    is_locked_ = true;
+    allocator_->NotifyLocked(unlocked_position_);
   }
 
-  // Overridden from DiscardableMemoryChunk:
-  bool Lock() override {
-    DCHECK(!is_locked_);
-    if (!data_)
-      return false;
-
-    is_locked_ = true;
-    allocator_->NotifyLocked(unlocked_position_);
-    return true;
-  }
-
-  void Unlock() override {
+  void Unlock() {
     DCHECK(is_locked_);
-    DCHECK(data_);
     is_locked_ = false;
     unlocked_position_ = allocator_->NotifyUnlocked(this);
   }
 
-  void* data() const override {
-    if (data_) {
-      DCHECK(is_locked_);
-      return data_.get();
-    }
-    return nullptr;
+  bool is_locked() const { return is_locked_; }
+  size_t size() const { return size_; }
+  void* data() const {
+    DCHECK(is_locked_);
+    return data_.get();
   }
 
-  size_t size() const { return size_; }
-
-  void Discard() {
-    DCHECK(!is_locked_);
-    data_.reset();
+  base::WeakPtr<OwnedMemoryChunk> GetWeakPtr() {
+    return weak_factory_.GetWeakPtr();
   }
 
  private:
   bool is_locked_;
   size_t size_;
   scoped_ptr<uint8_t[]> data_;
   DiscardableMemoryAllocator* allocator_;
 
-  std::list<DiscardableMemoryChunkImpl*>::iterator unlocked_position_;
+  std::list<OwnedMemoryChunk*>::iterator unlocked_position_;
+
+  base::WeakPtrFactory<OwnedMemoryChunk> weak_factory_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(OwnedMemoryChunk);
+};
+
+namespace {
+
+// Interface to the rest of the program. These objects are owned outside of the
+// allocator and wrap a weak ptr.
+class DiscardableMemoryChunkImpl : public base::DiscardableMemory {
+ public:
+  explicit DiscardableMemoryChunkImpl(
+      base::WeakPtr<DiscardableMemoryAllocator::OwnedMemoryChunk> chunk)
+      : memory_chunk_(chunk) {}
+  ~DiscardableMemoryChunkImpl() override {
+    // Either the memory chunk is invalid (because the backing has gone away),
+    // or the memory chunk is unlocked (because leaving the chunk locked once
+    // we deallocate means the chunk will never get cleaned up).
+    DCHECK(!memory_chunk_ || !memory_chunk_->is_locked());
+  }
+
+  // Overridden from DiscardableMemoryChunk:
+  bool Lock() override {
+    if (!memory_chunk_)
+      return false;
+
+    memory_chunk_->Lock();
+    return true;
+  }
+
+  void Unlock() override {
+    DCHECK(memory_chunk_);
+    memory_chunk_->Unlock();
+  }
+
+  void* data() const override {
+    if (memory_chunk_)
+      return memory_chunk_->data();
+    return nullptr;
+  }
+
+ private:
+  base::WeakPtr<DiscardableMemoryAllocator::OwnedMemoryChunk> memory_chunk_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(DiscardableMemoryChunkImpl);
 };
 
+}  // namespace
+
 DiscardableMemoryAllocator::DiscardableMemoryAllocator(
     size_t desired_max_memory)
     : desired_max_memory_(desired_max_memory),
       total_live_memory_(0u),
       locked_chunks_(0) {
 }
 
 DiscardableMemoryAllocator::~DiscardableMemoryAllocator() {
   DCHECK_EQ(0, locked_chunks_);
   STLDeleteElements(&live_unlocked_chunks_);
 }
 
 scoped_ptr<base::DiscardableMemory>
 DiscardableMemoryAllocator::AllocateLockedDiscardableMemory(size_t size) {
-  base::AutoLock lock(lock_);
-  scoped_ptr<DiscardableMemoryChunkImpl> chunk(
-      new DiscardableMemoryChunkImpl(size, this));
+  OwnedMemoryChunk* chunk = new OwnedMemoryChunk(size, this);
   total_live_memory_ += size;
   locked_chunks_++;
 
   // Go through the list of unlocked live chunks starting from the least
   // recently used, freeing as many as we can until we get our size under the
   // desired maximum.
   auto it = live_unlocked_chunks_.begin();
   while (total_live_memory_ > desired_max_memory_ &&
          it != live_unlocked_chunks_.end()) {
     total_live_memory_ -= (*it)->size();
-    (*it)->Discard();
+    delete *it;
     it = live_unlocked_chunks_.erase(it);
   }
 
-  return chunk.Pass();
+  return make_scoped_ptr(new DiscardableMemoryChunkImpl(chunk->GetWeakPtr()));
 }
 
-std::list<DiscardableMemoryAllocator::DiscardableMemoryChunkImpl*>::iterator
-DiscardableMemoryAllocator::NotifyUnlocked(DiscardableMemoryChunkImpl* chunk) {
-  base::AutoLock lock(lock_);
+std::list<DiscardableMemoryAllocator::OwnedMemoryChunk*>::iterator
+DiscardableMemoryAllocator::NotifyUnlocked(
+    DiscardableMemoryAllocator::OwnedMemoryChunk* chunk) {
   locked_chunks_--;
   return live_unlocked_chunks_.insert(live_unlocked_chunks_.end(), chunk);
 }
 
 void DiscardableMemoryAllocator::NotifyLocked(
-    std::list<DiscardableMemoryChunkImpl*>::iterator it) {
-  base::AutoLock lock(lock_);
+    std::list<OwnedMemoryChunk*>::iterator it) {
   locked_chunks_++;
   live_unlocked_chunks_.erase(it);
 }
 
-void DiscardableMemoryAllocator::NotifyDestructed(
-    std::list<DiscardableMemoryChunkImpl*>::iterator it) {
-  base::AutoLock lock(lock_);
-  live_unlocked_chunks_.erase(it);
-}
-
 }  // namespace html_viewer