Add SyncScheduler for scheduling CryptAuth enrollments and syncing devices.

components/proximity_auth/cryptauth/sync_scheduler_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 COMPONENTS_PROXIMITY_AUTH_CRYPTAUTH_CRYPTAUTH_SYNC_SCHEDULER_IMPL_H
+#define COMPONENTS_PROXIMITY_AUTH_CRYPTAUTH_CRYPTAUTH_SYNC_SCHEDULER_IMPL_H
+
+#include "base/timer/timer.h"
+#include "components/proximity_auth/cryptauth/sync_scheduler.h"
+
+namespace proximity_auth {
+
+// Implementation of SyncScheduler.
+class SyncSchedulerImpl : public SyncScheduler {
+ public:
+  // Creates the scheduler:
+  // |delegate|: Handles sync requests and must outlive the scheduler.
+  // |refresh_period|: The time to wait for the PERIODIC_REFRESH strategy.
+  // |base_recovery_period|: The initial time to wait for the
+  //    AGGRESSIVE_RECOVERY strategy. The time delta is increased for each
+  //    subsequent failure.
+  // |scheduler_name|: The name of the scheduler for debugging purposes.
+  SyncSchedulerImpl(Delegate* delegate,
+                    base::TimeDelta refresh_period,
+                    base::TimeDelta base_recovery_period,
+                    double max_jitter_percentage,
+                    const std::string& scheduler_name);

[Ilya Sherman, 2015/05/18 23:25:39]

nit: Please document the jitter percentage as well.

[Tim Song, 2015/05/19 22:13:19]

Done.

+
+  ~SyncSchedulerImpl() override;
+
+  // SyncScheduler:
+  void Start(const base::TimeDelta& elapsed_time_since_last_sync,
+             bool is_aggressive_recovery) override;

[Ilya Sherman, 2015/05/18 23:25:39]

Let's use an enum rather than a boolean for is_aggressive_recovery, so that call
sites are clearer.

[Tim Song, 2015/05/19 22:13:19]

Done.

+  void ForceSync() override;
+  base::TimeDelta GetTimeToNextSync() const override;
+  State GetState() const override;
+
+ protected:
+  // Creates and returns a base::Timer object. Exposed for testing.
+  virtual scoped_ptr<base::Timer> CreateTimer();
+
+ private:
+  // SyncScheduler:
+  void OnSyncCompleted(bool success) override;
+
+  // Called when |timer_| is fired.
+  void OnTimerFired();
+
+  // Schedules |timer_| for the next sync request.
+  void ScheduleNextSync(const base::TimeDelta& sync_delta);
+
+  // Randomly adds a random jitter to the value of GetPeriod(). The returned

[Ilya Sherman, 2015/05/18 23:25:39]

nit: "Randomly adds a random" -> "Adds a random"

[Tim Song, 2015/05/19 22:13:18]

Done.

+  // TimeDelta will be clamped to be non-negative.
+  base::TimeDelta GetJitteredPeriod();
+
+  // Returns the time to wait for the current strategy.
+  base::TimeDelta GetPeriod();
+
+  // The delegate handling sync requests when they are fired.
+  Delegate* const delegate_;
+
+  // The time to wait until the next refresh when the last sync attempt was
+  // successful.
+  const base::TimeDelta refresh_period_;
+
+  // The base recovery period for the AGGRESSIVE_RECOVERY strategy before
+  // backoffs are applied.
+  const base::TimeDelta base_recovery_period_;
+
+  // The maximum percentage (both positively and negatively) that the time to
+  // wait
+  // between each sync request is jittered. The jitter is randomly applied to
+  // each
+  // period so we can avoid deterministic behaviour.

[Ilya Sherman, 2015/05/18 23:25:39]

nit: Please re-wrap

[Ilya Sherman, 2015/05/18 23:25:39]

nit: We're not really trying to avoid deterministic behavior; we're just trying
to avoid lots of synchronized calls to the server -- right?

[Tim Song, 2015/05/19 22:13:19]

Done.

[Tim Song, 2015/05/19 22:13:19]

Done.

+  const double max_jitter_percentage_;
+
+  // The name of the scheduler used for debugging purposes.

[Ilya Sherman, 2015/05/18 23:25:39]

nit: "scheduler used" -> "scheduler, used"

[Tim Song, 2015/05/19 22:13:19]

Done.

+  const std::string scheduler_name_;
+
+  // The current state of the scheduler.
+  State state_;
+
+  // The number of failed syncs made in a row. Once a sync request succeeds,
+  // this counter is reset.
+  int failure_count_;

[Ilya Sherman, 2015/05/18 23:25:39]

nit: size_t?

[Tim Song, 2015/05/19 22:13:19]

Done.

+
+  // Timer firing for the next sync request.
+  scoped_ptr<base::Timer> timer_;
+
+  base::WeakPtrFactory<SyncSchedulerImpl> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncSchedulerImpl);
+};
+
+}  // namespace proximity_auth
+
+#endif  // COMPONENTS_PROXIMITY_CRYPTAUTH_CRYPTAUTH_SYNC_SCHEDULER_IMPL_H