Add SyncScheduler for scheduling CryptAuth enrollments and syncing devices.

components/proximity_auth/cryptauth/sync_scheduler_impl.cc

Index: components/proximity_auth/cryptauth/sync_scheduler_impl.cc
diff --git a/components/proximity_auth/cryptauth/sync_scheduler_impl.cc b/components/proximity_auth/cryptauth/sync_scheduler_impl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..42aa704391bba86ee88afad04c16d9ff9b8f9895
--- /dev/null
+++ b/components/proximity_auth/cryptauth/sync_scheduler_impl.cc
@@ -0,0 +1,186 @@
+// 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 "components/proximity_auth/cryptauth/sync_scheduler_impl.h"
+
+#include <algorithm>
+#include <cmath>
+#include <limits>
+
+#include "base/bind.h"
+#include "base/numerics/safe_conversions.h"
+#include "base/rand_util.h"
+#include "base/strings/stringprintf.h"
+#include "components/proximity_auth/logging/logging.h"
+
+namespace proximity_auth {
+
+namespace {
+
+// Returns a human readable string given a |time_delta|.
+std::string TimeDeltaToString(const base::TimeDelta& time_delta) {
+  if (time_delta.InDays() > 0)
+    return base::StringPrintf("%d days", time_delta.InDays());
+
+  if (time_delta.InHours() > 0)
+    return base::StringPrintf("%d hours", time_delta.InHours());
+
+  if (time_delta.InMinutes() > 0)
+    return base::StringPrintf("%d minutes", time_delta.InMinutes());
+
+  return base::StringPrintf("%d seconds",
+                            base::saturated_cast<int>(time_delta.InSeconds()));
+}
+
+}  // namespace
+
+SyncSchedulerImpl::SyncSchedulerImpl(Delegate* delegate,
+                                     base::TimeDelta refresh_period,
+                                     base::TimeDelta base_recovery_period,
+                                     double max_jitter_percentage,
+                                     const std::string& scheduler_name)
+    : delegate_(delegate),
+      refresh_period_(refresh_period),
+      base_recovery_period_(base_recovery_period),
+      max_jitter_percentage_(max_jitter_percentage),
+      scheduler_name_(scheduler_name),
+      state_(State::NOT_STARTED),
+      weak_ptr_factory_(this) {
+}
+
+SyncSchedulerImpl::~SyncSchedulerImpl() {
+}
+
+void SyncSchedulerImpl::Start(
+    const base::TimeDelta& elapsed_time_since_last_sync,
+    bool is_aggressive_recovery) {
+  state_ = is_aggressive_recovery ? State::AGGRESSIVE_RECOVERY
+                                  : State::PERIODIC_REFRESH;
+  // We reset the failure backoff when the scheduler is started again, as
+  // most likely the configuration that caused the previous attempts to fail
+  // most likely won't be present after a restart.

[Ilya Sherman, 2015/05/18 23:25:38]

nit: Double "most likely"

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

Done.

+  if (is_aggressive_recovery)
+    failure_count_ = 1;

[Ilya Sherman, 2015/05/18 23:25:38]

Why 1 and not 0?

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

This is so the backoff is calculated properly, as in failures, the
AGGRESSIVE_RECOVERY state has failure_count == 1.

+
+  // To take into account the time waited when the system is powered off, we
+  // subtract the time elapsed with a normal sync period to the initial time
+  // to wait.
+  base::TimeDelta sync_delta =
+      GetJitteredPeriod() - elapsed_time_since_last_sync;
+  if (sync_delta < base::TimeDelta::FromSeconds(0))
+    sync_delta = base::TimeDelta::FromSeconds(0);
+
+  ScheduleNextSync(sync_delta);
+}
+
+void SyncSchedulerImpl::ForceSync() {
+  OnTimerFired();
+}
+
+base::TimeDelta SyncSchedulerImpl::GetTimeToNextSync() const {
+  if (!timer_)
+    return base::TimeDelta::FromSeconds(0);
+  return timer_->GetCurrentDelay();
+}
+
+SyncScheduler::State SyncSchedulerImpl::GetState() const {
+  return state_;
+}
+
+void SyncSchedulerImpl::OnTimerFired() {
+  timer_.reset();
+  if (state_ == State::PERIODIC_REFRESH) {
+    PA_LOG(INFO) << "Timer fired for periodic refresh, making request...";
+    state_ = State::SYNCING_FOR_PERIODIC_REFRESH;
+  } else if (state_ == State::AGGRESSIVE_RECOVERY) {
+    PA_LOG(INFO) << "Timer fired for aggressive recovery, making request...";
+    state_ = State::SYNCING_FOR_AGGRESSIVE_RECOVERY;
+  } else {
+    PA_LOG(ERROR) << "Timer fired for unexpected state: "
+                  << static_cast<int>(state_);
+    return;
+  }
+
+  delegate_->OnSyncRequested(make_scoped_ptr(
+      new SyncRequest(weak_ptr_factory_.GetWeakPtr(),
+                      state_ == State::SYNCING_FOR_AGGRESSIVE_RECOVERY)));
+}
+
+scoped_ptr<base::Timer> SyncSchedulerImpl::CreateTimer() {
+  bool retain_user_task = false;
+  bool is_repeating = false;
+  return make_scoped_ptr(new base::Timer(retain_user_task, is_repeating));
+}
+
+void SyncSchedulerImpl::ScheduleNextSync(const base::TimeDelta& sync_delta) {
+  if (state_ != State::PERIODIC_REFRESH &&
+      state_ != State::AGGRESSIVE_RECOVERY) {
+    PA_LOG(ERROR) << "Unexpected state when scheduling next sync: state="
+                  << static_cast<int>(state_);
+  }
+
+  bool is_aggressive_recovery = (state_ == State::AGGRESSIVE_RECOVERY);
+  PA_LOG(INFO) << "Scheduling next sync for " << scheduler_name_ << ":\r\n"

[Ilya Sherman, 2015/05/18 23:25:38]

nit: Why "\r"?

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

I think this looks a bit more readable in the logs.

[Ilya Sherman, 2015/05/19 22:46:55]

Sorry, maybe my question wasn't clear enough.  Could "\r\n" be written as simply
"\n" or "\n\n" if you want two newlines?  "\r\n" is a Windows-ism that's
surprising to see in this context.

[Tim Song, 2015/05/20 00:13:22]

Done.

+               << "    Strategy: " << (is_aggressive_recovery
+                                           ? "Aggressive Recovery"
+                                           : "Periodic Refresh") << "\r\n"
+               << "    Time Delta: " << TimeDeltaToString(sync_delta)
+               << (is_aggressive_recovery
+                       ? base::StringPrintf("\r\n    Previous Failures: %d",
+                                            failure_count_)
+                       : "");
+
+  timer_ = CreateTimer();
+  timer_->Start(FROM_HERE, sync_delta,
+                base::Bind(&SyncSchedulerImpl::OnTimerFired,
+                           weak_ptr_factory_.GetWeakPtr()));
+}
+
+void SyncSchedulerImpl::OnSyncCompleted(bool success) {
+  if (state_ != State::SYNCING_FOR_PERIODIC_REFRESH &&
+      state_ != State::SYNCING_FOR_AGGRESSIVE_RECOVERY) {
+    PA_LOG(ERROR) << "Unexpected state when sync completed: state="
+                  << static_cast<int>(state_);
+    return;
+  }
+
+  if (success) {
+    state_ = State::PERIODIC_REFRESH;
+    failure_count_ = 0;
+  } else {
+    state_ = State::AGGRESSIVE_RECOVERY;
+    failure_count_++;

[Ilya Sherman, 2015/05/18 23:25:38]

nit: ++failure_count_

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

Done.

+  }
+
+  ScheduleNextSync(GetJitteredPeriod());
+}
+
+base::TimeDelta SyncSchedulerImpl::GetJitteredPeriod() {
+  double jitter = 2 * max_jitter_percentage_ * (base::RandDouble() - 0.5);
+  base::TimeDelta period = GetPeriod();
+  base::TimeDelta jittered_time_delta = period + (period * jitter);

[Ilya Sherman, 2015/05/18 23:25:38]

nit: It looks like "max_jitter_percentage_" is actually a simple ratio, not a
percentage (which is 100x a normal ratio).  Let's rename the variable for
clarity.

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

Done.

+  if (jittered_time_delta.InMilliseconds() < 0)
+    jittered_time_delta = base::TimeDelta::FromMilliseconds(0);
+  return jittered_time_delta;
+}
+
+base::TimeDelta SyncSchedulerImpl::GetPeriod() {
+  if (state_ == State::PERIODIC_REFRESH) {
+    return refresh_period_;
+  } else if (state_ == State::AGGRESSIVE_RECOVERY && failure_count_ > 0) {
+    // The backoff for each consecutive failure is exponentially doubled until
+    // it is equal to the normal refresh period.
+    // Note: |backoff_factor| may evaulate to INF if |failure_count_| is large,
+    // but multiplication operations for TimeDelta objects are saturated.
+    double backoff_factor = pow(2, failure_count_ - 1);
+    base::TimeDelta backoff_period = base_recovery_period_ * backoff_factor;
+    return backoff_period < refresh_period_ ? backoff_period : refresh_period_;
+  } else {
+    PA_LOG(ERROR) << "Error getting period in state: "
+                  << static_cast<int>(state_);
+    return base::TimeDelta();
+  }
+}
+
+}  // namespace proximity_auth