Architecture for cross-process memory notification suppressing

content/browser/memory/memory_message_filter.cc

Index: content/browser/memory/memory_message_filter.cc
diff --git a/content/browser/memory/memory_message_filter.cc b/content/browser/memory/memory_message_filter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4bee936c91365587e78fa28be679896e29285256
--- /dev/null
+++ b/content/browser/memory/memory_message_filter.cc
@@ -0,0 +1,47 @@
+// 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 "content/browser/memory/memory_message_filter.h"
+
+#include "content/browser/memory/memory_pressure_controller.h"
+#include "content/common/memory_messages.h"
+
+namespace content {
+namespace memory {
+
+MemoryMessageFilter::MemoryMessageFilter()
+    : BrowserMessageFilter(MemoryMsgStart) {}
+
+MemoryMessageFilter::~MemoryMessageFilter() {}
+
+void MemoryMessageFilter::OnFilterAdded(IPC::Sender* sender) {
+  MemoryPressureController::GetInstance()->OnMemoryMessageFilterAdded(this);
+}
+
+void MemoryMessageFilter::OnFilterRemoved() {
+  MemoryPressureController::GetInstance()->OnMemoryMessageFilterRemoved(this);
+}
+
+bool MemoryMessageFilter::OnMessageReceived(const IPC::Message& message) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(MemoryMessageFilter, message)
+    IPC_MESSAGE_HANDLER(MemoryHostMsg_SetPressureNotificationsSuppressedAck,
+                        OnSetPressureNotificationsSuppressedAck)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
+void MemoryMessageFilter::SendSetPressureNotificationsSuppressed(
+    bool suppressed) {
+  Send(new MemoryMsg_SetPressureNotificationsSuppressed(suppressed));
+}
+
+void MemoryMessageFilter::OnSetPressureNotificationsSuppressedAck() {

[Primiano Tucci (use gerrit), 2015/09/16 09:11:49]

This is probably unneeded (See my comment on the top of the cl)

[petrcermak, 2015/09/16 18:14:25]

As discussed offline, we will drop acks for the time being. The reason is that
there is currently no architecture to wait until memory pressure notifications
have been handled by all listeners. Even if we acked the request, the following
ordering of events would still be possible:


          BROWSER PROCESS                        CHILD PROCESS

                                          MemoryPressureListener::
                                        NotifyMemoryPressure(level) ===+
                                                                       |
                                                                       |
      MemoryPressureController::            IPC               PostTask |
  SetPressureNotificationsSuppressed -----------------+                |
    InAllProcesses(true, callback)                    :                |
                                                      :                |
                                                      V                |
                                           MemoryPressureListener::    |
                                      SetNotificationsSuppressed(true) |
                                                      :                |
                                                      :                |
           callback(true) <---------------------------+                |
                 :                       IPC (ACK)                     |
                 V                                                     |
     FALSE BELIEF THAT NO MEMORY                                       |
  PRESSURE HANDLING WILL OCCUR FROM                                    |
        THIS POINT ONWARDS                                             |
                                                                       |
                                          MemoryPressureListener:: <===+
                                                Notify(level)

Therefore, we will not support acks to avoid giving false
guarantees.

+  MemoryPressureController::GetInstance()
+      ->OnSetPressureNotificationsSuppressedResponse(this);
+}
+
+}  // namespace memory
+}  // namespace content