Add MediaServiceThrottler

media/base/android/media_service_throttler.h

+// Copyright 2016 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 MEDIA_BASE_ANDROID_MEDIA_SERVICE_THROTTLER_H_
+#define MEDIA_BASE_ANDROID_MEDIA_SERVICE_THROTTLER_H_
+
+#include <memory>
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/memory/singleton.h"
+#include "base/time/tick_clock.h"
+#include "base/time/time.h"
+
+namespace media {
+
+class MediaServiceThrottler {

[DaleCurtis, 2016/11/08 22:35:41]

MEDIA_EXPORT?

[tguilbert, 2016/11/11 03:50:29]

Done.

+ public:
+  // Called to get the singleton MediaServiceThrottler instance.
+  // The first thread on which GetInstance() is called is the thread on which
+  // calls to OnMediaServerCrash() will be signaled.
+  static MediaServiceThrottler* GetInstance();
+  virtual ~MediaServiceThrottler();

[sandersd (OOO until July 31), 2016/11/08 22:53:44]

Can the destructor be made protected? If you need it just for unit tests then a
subclass that redefines it as public would work for that.

[tguilbert, 2016/11/11 03:50:29]

Done.

+
+  // Returns the delay to wait until a new client is allowed to be created.
+  base::TimeDelta ScheduleClientCreation();

[sandersd (OOO until July 31), 2016/11/08 22:53:44]

This is misleading because the scheduling is only partial (a time is assigned
but nothing is actually configured to run at that time). I can't think of a more
clear name or a better factoring of the concerns, so probably just a more
detailed comment would be good.

[tguilbert, 2016/11/11 03:50:29]

Updated.

+
+  // Called by the MediaServerCrashListener whenever a crash is detected.
+  void OnMediaServerCrash();

[sandersd (OOO until July 31), 2016/11/08 22:53:44]

Should be protected or private.

[tguilbert, 2016/11/11 03:50:29]

Done.

+
+  void SetTickClockForTesting(base::TickClock* clock);
+
+  void ResetInternalStateForTesting();
+
+  base::TimeDelta GetBaseThrottlingRateForTesting();
+
+ private:
+  friend struct base::DefaultSingletonTraits<MediaServiceThrottler>;
+  MediaServiceThrottler();
+
+  // Updates |current_craches_| according to a linear decay function.
+  void UpdateServerCrashes();
+
+  // Ensures that the MediaServerCrashListener was properly started (can lead
+  // to OnMediaServerCrash() being called in the case it hasn't).
+  void EnsureCrashListenerStarted();
+
+  // Gets the delay for ScheduleClientCreation(), which grows exponentially
+  // based on |current_crashes_|.
+  base::TimeDelta GetThrottlingDelayFromServerCrashes();
+
+  std::unique_ptr<base::TickClock> clock_;
+  bool is_media_server_crash_listener_running_;
+
+  // Effective number of media server crashes.
+  double current_crashes_;
+
+  // Next time at which a client creation can be scheduled.
+  base::TimeTicks next_schedulable_slot_;
+
+  // Last media server crash time.
+  base::TimeTicks last_server_crash_;
+
+  // Last time UpdateServerCrashes() was called.
+  base::TimeTicks last_update_time_;

[sandersd (OOO until July 31), 2016/11/08 22:53:44]

Nit: add 'crash' to variable name for clarity.

[tguilbert, 2016/11/11 03:50:29]

Done.

+
+  // Last time ScheduleClientCreation() was called.
+  base::TimeTicks last_schedule_call_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaServiceThrottler);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_ANDROID_MEDIA_SERVICE_THROTTLER_H_