Add MemoryPurgeController

Source/platform/MemoryPurgeController.h

Index: Source/platform/MemoryPurgeController.h
diff --git a/Source/platform/MemoryPurgeController.h b/Source/platform/MemoryPurgeController.h
new file mode 100644
index 0000000000000000000000000000000000000000..86c7de3ba402252bfda812d156be63b906adec76
--- /dev/null
+++ b/Source/platform/MemoryPurgeController.h
@@ -0,0 +1,72 @@
+// 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.
+
+#ifndef MemoryPurgeController_h
+#define MemoryPurgeController_h
+
+#include "platform/PlatformExport.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+enum class MemoryPurgeMode {
+    // The tab contains the webview went to background
+    InactiveTab,
+    // TODO(bashi): Add more modes as needed.
+};
+
+enum class DeviceKind {
+    NotSpecified,
+    LowEnd,
+};
+
+// Classes which have discardable/reducible memory can implement this
+// interface to be informed when they should reduce memory consumption.
+class MemoryPurgeClient : public WillBeGarbageCollectedMixin {
+public:
+    virtual ~MemoryPurgeClient() { }
+
+    // MemoryPurgeController invokes this callback when a memory purge event
+    // has occurred.
+    virtual void purgeMemory(MemoryPurgeMode, DeviceKind) = 0;
+
+    DECLARE_TRACE();
+};
+
+// MemoryPurgeController listens to some events which could be opportunities
+// for reducing memory consumption and notifies its clients.
+// Since we want to controll memory per tab, MemoryPurgeController is owned by

[haraken, 2015/08/25 03:46:08]

control

[bashi, 2015/08/25 04:52:58]

Done.

+// Page.
+class PLATFORM_EXPORT MemoryPurgeController {
+public:
+    MemoryPurgeController();
+
+    void registerClient(MemoryPurgeClient* client)

[tkent, 2015/08/25 03:45:59]

Is it ok to call registerClient/unregisterClient from non-main threads?

[bashi, 2015/08/25 04:52:58]

Added ASSERT(isMainThead())

+    {
+        ASSERT(client);

[haraken, 2015/08/25 03:46:08]

Add ASSERT(!m_clients.contains(client)).

[bashi, 2015/08/25 04:52:58]

Done.

+        m_clients.add(client);
+    }
+
+    void unregisterClient(MemoryPurgeClient* client)

[tkent, 2015/08/25 03:45:59]

How to call unregisterClient() for an object which is already GarbageCollected?

[haraken, 2015/08/25 03:47:03]

This will be used only when we want to explicitly unregister the client from the
controller.

[tkent, 2015/08/25 03:50:19]

m_clients consists of raw pointers now (!ENABLE(OILPAN)).  So, if a
GarbageCollected object implements MemoryPurgeClient, it needs to unregister
itself when it's destructed.

[haraken, 2015/08/25 03:52:35]

Yes, I'm assuming the following use case.

class X : public RefCountedWillBeGarbageCollected<X>, public MemoryPurgeClient {
  ~X() {
#if !ENABLE(OILPAN)
    unregisterClient(this);
#endif
  }

  void someDisposal() {
    unregisterClient(this);
  }
};

[tkent, 2015/08/25 04:58:08]

I'm asking about GarbageCollected(Finalized) cases, not WillBe.

+    {
+        ASSERT(m_clients.contains(client));
+        m_clients.remove(client);
+    }
+
+    // Called when page visibility changed.
+    void pageBecameVisible();
+    void pageBecameHidden();
+
+    DECLARE_TRACE();
+
+private:
+    void purgeMemory(MemoryPurgeMode);
+
+    WillBeHeapHashSet<RawPtrWillBeWeakMember<MemoryPurgeClient>> m_clients;
+    DeviceKind m_deviceKind;
+};
+
+} // namespace blink
+
+#endif // MemoryPurgeController_h