sync: beginnings of MessageLoop based SyncerThread

chrome/browser/sync/engine/syncer_thread2.h

+// Copyright (c) 2011 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.
+//
+// A class to run the syncer on a thread.
+#ifndef CHROME_BROWSER_SYNC_ENGINE_SYNCER_THREAD2_H_
+#define CHROME_BROWSER_SYNC_ENGINE_SYNCER_THREAD2_H_
+#pragma once
+
+#include "base/linked_ptr.h"
+#include "base/observer_list.h"
+#include "base/task.h"
+#include "base/threading/thread.h"
+#include "base/time.h"
+#include "base/timer.h"
+#include "chrome/browser/sync/engine/nudge_source.h"
+#include "chrome/browser/sync/engine/polling_constants.h"
+#include "chrome/browser/sync/sessions/sync_session.h"
+#include "chrome/browser/sync/sessions/sync_session_context.h"
+
+namespace browser_sync {
+
+struct ServerConnectionEvent;
+class Syncer;
+
+namespace s3 {
+
+class SyncerThread : public sessions::SyncSession::Delegate {
+ public:
+  enum Mode {
+    // In this mode, the thread only performs configuration tasks.  This is
+    // designed to make the case where we want to download updates for a
+    // specific type only, and not continue syncing until we are moved into
+    // normal mode.
+    CONFIGURATION_MODE,
+    // Resumes polling and allows nudges, drops configuration tasks.  Runs
+    // through entire sync cycle.
+    NORMAL_MODE,
+  };
+
+  // Takes ownership of both |context| and |syncer|.
+  SyncerThread(sessions::SyncSessionContext* context, Syncer* syncer);
+  virtual ~SyncerThread();
+
+  // Change the mode of operation.
+  // We don't use a lock when changing modes, so we won't cause currently
+  // scheduled jobs to adhere to the new mode.  We could protect it, but it
+  // doesn't buy very much as a) a session could already be in progress and it
+  // will continue no matter what, b) the scheduled sessions already contain
+  // all their required state and won't be affected by potential change at
+  // higher levels (i.e. the registrar), and c) we service tasks FIFO, so once
+  // the mode changes all future jobs will be run against the updated mode.
+  void Start(Mode mode);
+
+  // Joins on the thread as soon as possible (currently running session
+  // completes).
+  void Stop();
+
+  // The meat and potatoes.
+  void ScheduleNudge(const base::TimeDelta& delay, NudgeSource source,
+                     const syncable::ModelTypeBitSet& types);
+  void ScheduleConfig(const base::TimeDelta& delay,
+                      const syncable::ModelTypeBitSet& types);
+
+  // Change status of notifications in the SyncSessionContext.
+  void set_notifications_enabled(bool notifications_enabled);
+
+  // DDOS avoidance function.  Calculates how long we should wait before trying
+  // again after a failed sync attempt, where the last delay was |base_delay|.
+  // TODO(tim): Look at URLRequestThrottlerEntryInterface.
+  static base::TimeDelta GetRecommendedDelay(const base::TimeDelta& base_delay);
+
+  // SyncSession::Delegate implementation.
+  virtual void OnSilencedUntil(const base::TimeTicks& silenced_until);
+  virtual bool IsSyncingCurrentlySilenced();
+  virtual void OnReceivedShortPollIntervalUpdate(
+      const base::TimeDelta& new_interval);
+  virtual void OnReceivedLongPollIntervalUpdate(
+      const base::TimeDelta& new_interval);
+  virtual void OnShouldStopSyncingPermanently();
+
+ private:
+  friend class SyncerThread2Test;
+
+  // State pertaining to exponential backoff or throttling periods.
+  struct WaitInterval {
+    enum Mode {
+      // A wait interval whose duration has been affected by exponential
+      // backoff.
+      // EXPONENTIAL_BACKOFF intervals are nudge-rate limited to 1 per interval.
+      EXPONENTIAL_BACKOFF,
+      // A server-initiated throttled interval.  We do not allow any syncing
+      // during such an interval.
+      THROTTLED,
+    };
+    Mode mode;
+
+    // This bool is set to true if we have observed a nudge during this
+    // interval and mode == EXPONENTIAL_BACKOFF.
+    bool had_nudge;
+    base::TimeDelta length;
+    base::OneShotTimer<SyncerThread> timer;
+    WaitInterval(Mode mode, base::TimeDelta length);
+  };
+
+  // Internal state for every sync task that is scheduled.
+  struct SyncSessionJob {
+    // An enum used to describe jobs for scheduling purposes.
+    enum Purpose {
+      // Our poll timer schedules POLL jobs periodically based on a server
+      // assigned poll interval.
+      POLL,
+      // A nudge task can come from a variety of components needing to force
+      // a sync.  The source is inferable from |session.source()|.
+      NUDGE,
+      // Typically used for fetching updates for a subset of the enabled types
+      // during initial sync or reconfiguration.  We don't run all steps of
+      // the sync cycle for these (e.g. CleanupDisabledTypes is skipped).
+      CONFIGURATION,
+    };
+
+    Purpose purpose;
+    base::TimeTicks scheduled_start;
+    linked_ptr<sessions::SyncSession> session;
+  };
+
+  // A component used to get time delays associated with exponential backoff.
+  // Encapsulated into a class to facilitate testing.
+  class DelayProvider {
+   public:
+    DelayProvider();
+    virtual base::TimeDelta GetDelay(const base::TimeDelta& last_delay);
+    virtual ~DelayProvider();
+   private:
+    DISALLOW_COPY_AND_ASSIGN(DelayProvider);
+  };
+
+  // Helper to assemble a job and post a delayed task to sync.
+  void ScheduleSyncSessionJob(const base::TimeDelta& delay,
+                              SyncSessionJob::Purpose purpose,
+                              sessions::SyncSession* session);
+
+  // Invoke the Syncer to perform a sync.
+  void DoSyncSessionJob(const SyncSessionJob& job);
+
+  // Called after the Syncer has performed the sync represented by |job|, to
+  // reset our state.
+  void FinishSyncSessionJob(const SyncSessionJob& job);
+
+  // Helper to FinishSyncSessionJob to schedule the next sync operation.
+  void ScheduleNextSync(const SyncSessionJob& old_job);
+
+  // Helper to configure polling intervals. Used by Start and ScheduleNextSync.
+  void AdjustPolling(const SyncSessionJob* old_job);
+
+  // Helper to ScheduleNextSync in case of consecutive sync errors.
+  void HandleConsecutiveContinuationError(const SyncSessionJob& old_job);
+
+  // Determines if it is legal to run a sync job for |purpose| at
+  // |scheduled_start|.  This checks current operational mode, backoff or
+  // throttling, freshness (so we don't make redundant syncs), and connection.
+  bool ShouldRunJob(SyncSessionJob::Purpose purpose,
+                    const base::TimeTicks& scheduled_start);
+
+  // 'Impl' here refers to real implementation of public functions, running on
+  // |thread_|.
+  void StartImpl(Mode mode);
+  void ScheduleNudgeImpl(const base::TimeDelta& delay,
+                         NudgeSource source,
+                         const syncable::ModelTypeBitSet& model_types);
+  void ScheduleConfigImpl(const base::TimeDelta& delay,
+                          const ModelSafeRoutingInfo& routing_info,
+                          const std::vector<ModelSafeWorker*>& workers);
+
+  // Returns true if the client is currently in exponential backoff.
+  bool IsBackingOff() const;
+
+  // Helper to signal all listeners registered with |session_context_|.
+  void Notify(SyncEngineEvent::EventCause cause);
+
+  // ServerConnectionEventListener implementation.
+  // TODO(tim): schedule a nudge when valid connection detected? in 1 minute?
+  virtual void OnServerConnectionEvent(const ServerConnectionEvent& event);
+
+  // Callback to change backoff state.
+  void DoCanaryJob();
+  void Unthrottle();
+
+  // Creates a session for a poll and performs the sync.
+  void PollTimerCallback();
+
+  base::Thread thread_;
+
+  // Modifiable versions of kDefaultLongPollIntervalSeconds which can be
+  // updated by the server.
+  base::TimeDelta syncer_short_poll_interval_seconds_;
+  base::TimeDelta syncer_long_poll_interval_seconds_;
+
+  // Periodic timer for polling.  See AdjustPolling.
+  base::RepeatingTimer<SyncerThread> poll_timer_;
+
+  // The mode of operation. We don't use a lock, see Start(...) comment.
+  Mode mode_;
+
+  // TODO(tim): Bug 26339. This needs to track more than just time I think,
+  // since the nudges could be for different types. Current impl doesn't care.
+  base::TimeTicks last_sync_session_end_time_;
+
+  // Have we observed a valid server connection?
+  bool server_connection_ok_;
+
+  // Tracks in-flight nudges so we can coalesce.
+  scoped_ptr<SyncSessionJob> pending_nudge_;
+
+  // Current wait state.  Null if we're not in backoff and not throttled.
+  scoped_ptr<WaitInterval> wait_interval_;
+
+  scoped_ptr<DelayProvider> delay_provider_;
+
+  // Invoked to run through the sync cycle.
+  scoped_ptr<Syncer> syncer_;
+
+  scoped_ptr<sessions::SyncSessionContext> session_context_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncerThread);
+};
+
+// The SyncerThread manages its own internal thread and thus outlives it. We
+// don't need refcounting for posting tasks to this internal thread.
+DISABLE_RUNNABLE_METHOD_REFCOUNT(SyncerThread);
+
+}  // namespace s3
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_ENGINE_SYNCER_THREAD2_H_