Architecture for cross-process memory notification suppressing

content/browser/memory/memory_message_filter.h

Index: content/browser/memory/memory_message_filter.h
diff --git a/content/browser/memory/memory_message_filter.h b/content/browser/memory/memory_message_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..ac4cbb5a6cd87baa65d4fadd0aee7f1e636625af
--- /dev/null
+++ b/content/browser/memory/memory_message_filter.h
@@ -0,0 +1,38 @@
+// 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 CONTENT_BROWSER_MEMORY_MEMORY_MESSAGE_FILTER_H_
+#define CONTENT_BROWSER_MEMORY_MEMORY_MESSAGE_FILTER_H_
+
+#include "content/public/browser/browser_message_filter.h"
+
+namespace content {
+namespace memory {

[Primiano Tucci (use gerrit), 2015/09/16 09:11:50]

Probably this memory namespace is superfluous. At the end you have 3 classes
(which have all "Memory" in their names), doesn't really justify a namespace.
The other similar classes seem to just live in content.

[petrcermak, 2015/09/16 18:14:26]

Done.

+
+// This class sends and receives memory messages on the browser process.
+// See also: child_memory_message_filter.h
+class MemoryMessageFilter : public BrowserMessageFilter {
+ public:
+  MemoryMessageFilter();
+
+  // BrowserMessageFilter implementation.
+  void OnFilterAdded(IPC::Sender* sender) override;
+  void OnFilterRemoved() override;

[Primiano Tucci (use gerrit), 2015/09/16 09:11:50]

Plz doublecheck but I think you really want here is OnChannelConnected /
OnChannelClosing.
I don't think you can send messages between OnFilterAdded and
OnCHannelConnected, and similarly the IPC::Sender* becomes null between
OnChannelClosing and OnFilterRemoved (so if you try to send a message then you
get a nullptr)

[petrcermak, 2015/09/16 18:14:26]

I've searched through the Chromium source code and found the following:

ADD FILTER

OnChannelConnected(int32 peer_id)
does not guarantee that the sender has already been set. Consequently, the
initial message to suppress memory pressure notifications in a newly created
process could be dropped.

OnFilterAdded(IPC::Sender* sender)
is the right option here because it is called immediately after the sender is
set:
https://code.google.com/p/chromium/codesearch#chromium/src/content/public/bro....

REMOVE FILTER

OnChannelClosing()
is the right option because is called immediately after the sender is unset:
https://code.google.com/p/chromium/codesearch#chromium/src/content/public/bro....

OnFilterRemoved()
would work as well because it is guaranteed to be called immediately after
OnChannelClosing. Moreover, BrowserMessageFilter::Send() checks if the
underlying sender is null (so we could override this method even if it were
after the sender was unset).

SUMMARY

OnFilterAdded(IPC::Sender* sender) and OnChannelClosing() are the right methods
to override here.

+  bool OnMessageReceived(const IPC::Message& message) override;
+
+  void SendSetPressureNotificationsSuppressed(bool suppressed);
+
+ protected:
+  ~MemoryMessageFilter() override;
+
+  void OnSetPressureNotificationsSuppressedAck();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MemoryMessageFilter);
+};
+
+}  // namespace memory
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEMORY_MEMORY_MESSAGE_FILTER_H_