Provide renderers with memory pressure signals.

content/browser/memory/memory_pressure_controller_impl.h

 // 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_PRESSURE_CONTROLLER_H_
-#define CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_H_
+#ifndef CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_IMPL_H_
+#define CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_IMPL_H_
 
 #include <map>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/singleton.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 class BrowserChildProcessHost;
 class MemoryMessageFilter;
 class RenderProcessHost;
 
-class CONTENT_EXPORT MemoryPressureController {
+// Controller for memory pressure IPC messages. Each child process owns and
+// registers a MemoryMessageFilter, which can be used to both suppress and
+// simulate memory pressure messages across processes. This controller
+// coordinates suppressing and simulation of messages, as well as allows for
+// messages to be forwarded to individual processes. This allows the browser
+// process to control what memory pressure messages are seen in child processes.
+// For more details see content/browser/memory/memory_message_filter.h and
+// content/child/memory/child_memory_message_filter.h.
+class CONTENT_EXPORT MemoryPressureControllerImpl {
  public:
+  // This method can be called from any thread.
+  static MemoryPressureControllerImpl* GetInstance();
+
   // These methods must be called on the IO thread.
   void OnMemoryMessageFilterAdded(MemoryMessageFilter* filter);
   void OnMemoryMessageFilterRemoved(MemoryMessageFilter* filter);
 
   // These methods can be called from any thread.
+
+  // Suppresses all memory pressure messages from passing through all attached
+  // MemoryMessageFilters. Any messages sent through a "suppressed" filter will
+  // be ignored on the receiving end.
   void SetPressureNotificationsSuppressedInAllProcesses(bool suppressed);
+
+  // Simulates memory pressure in all processes by invoking
+  // SimulatePressureNotification on all attached MemoryMessageFilters. These
+  // messages will be received even if suppression is enabled.
   void SimulatePressureNotificationInAllProcesses(
       base::MemoryPressureListener::MemoryPressureLevel level);
+
+  // Sends a memory pressure notification to the specified browser child process
+  // via its attached MemoryMessageFilter.
   void SendPressureNotification(
       const BrowserChildProcessHost* child_process_host,
       base::MemoryPressureListener::MemoryPressureLevel level);
+
+  // Sends a memory pressure notification to the specified renderer process via
+  // its attached MemoryMessageFilter.
   void SendPressureNotification(
       const RenderProcessHost* render_process_host,
       base::MemoryPressureListener::MemoryPressureLevel level);
 
-  // This method can be called from any thread.
-  static MemoryPressureController* GetInstance();
-
  protected:
-  virtual ~MemoryPressureController();
+  virtual ~MemoryPressureControllerImpl();
 
  private:
-  friend struct base::DefaultSingletonTraits<MemoryPressureController>;
+  friend struct base::DefaultSingletonTraits<MemoryPressureControllerImpl>;
 
-  MemoryPressureController();
+  MemoryPressureControllerImpl();
 
   // Implementation of the various SendPressureNotification methods.
   void SendPressureNotificationImpl(
       const void* child_process_host,
       base::MemoryPressureListener::MemoryPressureLevel level);
 
   // Map from untyped process host pointers to the associated memory message
   // filters in the browser process. Always accessed on the IO thread.
   typedef std::map<const void*, scoped_refptr<MemoryMessageFilter>>
       MemoryMessageFilterMap;
   MemoryMessageFilterMap memory_message_filters_;
 
-  DISALLOW_COPY_AND_ASSIGN(MemoryPressureController);
+  DISALLOW_COPY_AND_ASSIGN(MemoryPressureControllerImpl);
 };
 
 }  // namespace content
 
-#endif  // CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_H_
+#endif  // CONTENT_BROWSER_MEMORY_MEMORY_PRESSURE_CONTROLLER_IMPL_H_