[Not for review] Discardable memory emulation

content/renderer/render_process_discardable_memory_provider.cc

+// Copyright (c) 2012 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 "content/renderer/render_process_discardable_memory_provider.h"
+
+namespace content {
+
+namespace {
+
+class EmulatedDiscardableMemory : public base::DiscardableMemory {
+ public:
+  EmulatedDiscardableMemory(RenderProcessDiscardableMemoryProvider* provider)
+      : provider_(provider) {
+  }
+
+  virtual ~EmulatedDiscardableMemory() {
+  }
+
+  virtual bool InitializeAndLock(size_t size) OVERRIDE {
+    if (provider_->Register(this, size))
+      return Lock() != base::DISCARDABLE_MEMORY_FAILED;
+    return false;
+  }
+
+  virtual base::LockDiscardableMemoryStatus Lock() OVERRIDE {
+    return provider_->Lock(this);
+  }
+
+  virtual void Unlock() OVERRIDE {
+    provider_->Unlock(this);
+  }
+
+  virtual void* Memory() const OVERRIDE {
+    return provider_->Memory(this);
+  }
+
+ private:
+  RenderProcessDiscardableMemoryProvider* provider_;
+
+  DISALLOW_COPY_AND_ASSIGN(EmulatedDiscardableMemory);
+};
+
+}  // namespace
+
+RenderProcessDiscardableMemoryProvider::
+    RenderProcessDiscardableMemoryProvider()
+    : visible_(false) {
+}
+
+RenderProcessDiscardableMemoryProvider::
+    ~RenderProcessDiscardableMemoryProvider() {
+  AllocationMap::iterator it = allocations_.begin();
+  for (; it != allocations_.end(); ++it)
+    if (it->second.memory != NULL)
+      free(it->second.memory);
+}
+
+void RenderProcessDiscardableMemoryProvider::RenderProcessVisibilityChanged(
+    bool visible) {
+  visible_ = visible;
+  EnforcePolicy();
+}
+
+bool RenderProcessDiscardableMemoryProvider::Register(
+    const base::DiscardableMemory* discardable, size_t size) {
+  Unregister(discardable);
+  AllocatedMemory allocation = { NULL, false, size };
+  allocation.memory = malloc(size * sizeof(char));
+  if (allocation.memory == NULL)
+    return false;
+  allocations_[discardable] = allocation;
+  return true;
+}
+
+void RenderProcessDiscardableMemoryProvider::Unregister(
+    const base::DiscardableMemory* discardable) {
+  AllocationMap::iterator it = allocations_.find(discardable);
+  if (it == allocations_.end())
+    return;
+  DCHECK(!it->second.locked);
+  if (it->second.memory != NULL)
+    free(it->second.memory);
+  allocations_.erase(it);
+}
+
+base::LockDiscardableMemoryStatus RenderProcessDiscardableMemoryProvider::Lock(
+    const base::DiscardableMemory* discardable) {
+  AllocationMap::iterator it = allocations_.find(discardable);
+  if (it == allocations_.end())
+    return base::DISCARDABLE_MEMORY_FAILED;
+
+  it->second.locked = true;
+  if (it->second.memory != NULL)
+    return base::DISCARDABLE_MEMORY_SUCCESS;
+
+  it->second.memory = malloc(it->second.size * sizeof(char));
+  return base::DISCARDABLE_MEMORY_PURGED;
+}
+
+void RenderProcessDiscardableMemoryProvider::Unlock(
+    const base::DiscardableMemory* discardable) {
+  AllocationMap::iterator it = allocations_.find(discardable);
+  if (it == allocations_.end())
+    return;
+  it->second.locked = false;
+}
+
+void* RenderProcessDiscardableMemoryProvider::Memory(
+    const base::DiscardableMemory* discardable) const {
+  AllocationMap::const_iterator it = allocations_.find(discardable);
+  DCHECK(it->second.locked);
+  if (it == allocations_.end())
+    return NULL;
+  return it->second.memory;
+}
+
+base::DiscardableMemory* RenderProcessDiscardableMemoryProvider::
+    CreateDiscardableMemory() {
+  return new EmulatedDiscardableMemory(this);
+}
+
+bool RenderProcessDiscardableMemoryProvider::PurgeForTestingSupported() const {
+  return true;
+}
+
+void RenderProcessDiscardableMemoryProvider::PurgeForTesting() {
+  Purge();
+}
+
+void RenderProcessDiscardableMemoryProvider::Purge() {
+  AllocationMap::iterator it = allocations_.begin();
+  for (; it != allocations_.end(); ++it) {
+    if (it->second.memory != NULL && !it->second.locked) {
+      free(it->second.memory);
+      it->second.memory = NULL;
+    }
+  }
+}
+
+// We could be smarter here and use a MRU scheme and memory limits. Instead,
+// we'll just purge everything when the process is no longer visible.
+void RenderProcessDiscardableMemoryProvider::EnforcePolicy() {
+  if (!visible_)
+    Purge();
+}
+
+}  // namespace content