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/cancelable_callback.h"
+#include "base/macros.h"
+#include "base/lazy_instance.h"
+#include "base/single_thread_task_runner.h"
+#include "base/time/tick_clock.h"
+#include "base/time/time.h"
+#include "media/base/media_export.h"
+
+namespace media {
+class MediaServerCrashListener;
+
+class MEDIA_EXPORT MediaServiceThrottler {
+ 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();
+
+  // Returns the delay to wait until a new client is allowed to be created.
+  base::TimeDelta GetDelayForClientCreation();
+
+  void SetTickClockForTesting(base::TickClock* clock);

[DaleCurtis, 2016/11/11 23:32:16]

Usually I'd put these as a single block with a comment "// Test only methods."
to delineate the API a bit more clearly.

[tguilbert, 2016/11/14 23:18:08]

Done.

+
+  void ResetInternalStateForTesting();
+
+  base::TimeDelta GetBaseThrottlingRateForTesting();
+
+  bool IsCrashListenerAliveForTesting();
+
+  void SetCrashListenerTaskRunnerForTesting(
+      scoped_refptr<base::SingleThreadTaskRunner> crash_listener_task_runner);
+
+ private:
+  friend struct base::DefaultLazyInstanceTraits<MediaServiceThrottler>;
+  friend class MediaServiceThrottlerTest;

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

Is adding tests as a friend class frowned upon? sandersd@, you mentioned having
a subclass redefining certain things as public. Is this the preferred way to go?

[sandersd (OOO until July 31), 2016/11/11 18:55:14]

Friend classes are fine for testing, and common in Chromium.

Note though that the friendship is with the base test class, not the test cases,
so you have to forward everything through your own methods anyway. In many such
cases I find that subclassing is cleaner, and is more likely to eliminate
ForTesting() methods (which are an anti-pattern, even if they are popular in
Chromium).

+
+  MediaServiceThrottler();
+  virtual ~MediaServiceThrottler();
+
+  // Called by the |crash_listener_| whenever a crash is detected.
+  void OnMediaServerCrash();
+
+  // 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();
+
+  // Frees up the resources used by |crash_listener_|;
+  void ReleaseCrashListener();
+
+  // Gets the delay for ScheduleClientCreation(), which grows exponentially
+  // based on |current_crashes_|.
+  base::TimeDelta GetThrottlingDelayFromServerCrashes();
+
+  std::unique_ptr<base::TickClock> clock_;
+
+  // Effective number of media server crashes.

[DaleCurtis, 2016/11/11 23:32:16]

Explain why it's a double.

[tguilbert, 2016/11/14 23:18:08]

Done.

+  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_current_crash_update_time_;
+
+  // Last time ScheduleClientCreation() was called.
+  base::TimeTicks last_schedule_call_;
+
+  // Callbacks used to release |crash_listener_| after 60s of inactivity.
+  base::Closure release_crash_listener_cb_;
+  base::CancelableClosure cancelable_release_crash_listener_cb_;
+
+  // Listener that verifies
+  std::unique_ptr<MediaServerCrashListener> crash_listener_;
+
+  scoped_refptr<base::SingleThreadTaskRunner> crash_listener_task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaServiceThrottler);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_ANDROID_MEDIA_SERVICE_THROTTLER_H_