Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_emulated.cc

+// Copyright 2013 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 "base/memory/discardable_memory.h"
+
+#include "base/memory/discardable_memory_provider.h"
+
+using base::internal::DiscardableMemoryProvider;
+
+namespace base {
+namespace {
+
+class DiscardableMemoryEmulated : public DiscardableMemory {
+ public:
+  explicit DiscardableMemoryEmulated(size_t size) : is_locked_(false) {
+    DiscardableMemoryProvider::GetInstance()->Register(this, size);
+  }
+
+  virtual ~DiscardableMemoryEmulated() {
+    if (is_locked_)
+      Unlock();
+    DiscardableMemoryProvider::GetInstance()->Unregister(this);
+  }
+
+  // DiscardableMemory:
+  virtual LockDiscardableMemoryStatus Lock() OVERRIDE {
+    DCHECK(!is_locked_);
+
+    bool purged = false;
+    memory_ = DiscardableMemoryProvider::GetInstance()->Acquire(this, &purged);
+    if (!memory_)
+      return DISCARDABLE_MEMORY_FAILED;
+
+    is_locked_ = true;
+    return purged ? DISCARDABLE_MEMORY_PURGED : DISCARDABLE_MEMORY_SUCCESS;
+  }
+
+  virtual void Unlock() OVERRIDE {
+    DCHECK(is_locked_);
+    DiscardableMemoryProvider::GetInstance()->Release(this, memory_.Pass());
+    is_locked_ = false;
+  }
+
+  virtual void* Memory() const OVERRIDE {
+    DCHECK(memory_);
+    return memory_.get();
+  }
+
+ private:
+  scoped_ptr<uint8, FreeDeleter> memory_;
+  bool is_locked_;
+
+  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryEmulated);
+};
+
+}  // namespace
+
+// static
+bool DiscardableMemory::SupportedNatively() {
+  return false;
+}
+
+// static
+scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemory(
+    size_t size) {
+  scoped_ptr<DiscardableMemory> memory(new DiscardableMemoryEmulated(size));
+  if (!memory)
+    return scoped_ptr<DiscardableMemory>();
+  if (memory->Lock() != DISCARDABLE_MEMORY_PURGED)

[Philippe, 2013/11/05 12:41:39]

I was playing on Linux with discardable memory (thanks to this CL :)) and came
across this line. Is the use of DISCARDABLE_MEMORY_PURGED here (instead of
DISCARDABLE_MEMORY_SUCCESS) intentional?

+    return scoped_ptr<DiscardableMemory>();
+  return memory.Pass();
+}
+
+// static
+bool DiscardableMemory::PurgeForTestingSupported() {
+  return true;
+}
+
+// static
+void DiscardableMemory::PurgeForTesting() {
+  DiscardableMemoryProvider::GetInstance()->PurgeAll();
+}
+
+}  // namespace base