make new syncer thread the default.

chrome/browser/sync/engine/syncer_thread.h

Index: chrome/browser/sync/engine/syncer_thread.h
diff --git a/chrome/browser/sync/engine/syncer_thread.h b/chrome/browser/sync/engine/syncer_thread.h
index d270f14000d127431ceff0ce7b804ec8a8acce0a..11fee167958b5f88dd7db4d1ce0c3f900d5aff5e 100644
--- a/chrome/browser/sync/engine/syncer_thread.h
+++ b/chrome/browser/sync/engine/syncer_thread.h
@@ -3,74 +3,175 @@
 // found in the LICENSE file.
 //
 // A class to run the syncer on a thread.
-// This is the default implementation of SyncerThread whose Stop implementation
-// does not support a timeout, but is greatly simplified.
 #ifndef CHROME_BROWSER_SYNC_ENGINE_SYNCER_THREAD_H_
 #define CHROME_BROWSER_SYNC_ENGINE_SYNCER_THREAD_H_
 #pragma once
 
-#include <list>
-#include <string>
-#include <vector>
-
-#include "base/basictypes.h"
-#include "base/gtest_prod_util.h"
-#include "base/memory/ref_counted.h"
+#include "base/callback.h"
+#include "base/memory/linked_ptr.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/synchronization/condition_variable.h"
+#include "base/observer_list.h"
+#include "base/task.h"
 #include "base/threading/thread.h"
 #include "base/time.h"
-#include "base/synchronization/waitable_event.h"
-#include "chrome/browser/sync/engine/syncer_types.h"
-#include "chrome/browser/sync/sessions/sync_session.h"
-#include "chrome/browser/sync/syncable/model_type.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/engine/syncer.h"
 #include "chrome/browser/sync/syncable/model_type_payload_map.h"
-#include "chrome/common/deprecated/event_sys-inl.h"
-
-#if defined(OS_LINUX)
-#include "chrome/browser/sync/engine/idle_query_linux.h"
-#endif
-
-class EventListenerHookup;
+#include "chrome/browser/sync/engine/net/server_connection_manager.h"
+#include "chrome/browser/sync/sessions/sync_session.h"
+#include "chrome/browser/sync/sessions/sync_session_context.h"
 
 namespace browser_sync {
 
-class ModelSafeWorker;
-class ServerConnectionManager;
-class Syncer;
-class URLFactory;
 struct ServerConnectionEvent;
 
-class SyncerThread : public base::RefCountedThreadSafe<SyncerThread>,
-                     public sessions::SyncSession::Delegate {
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadTest, CalculateSyncWaitTime);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadTest, CalculatePollingWaitTime);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, Polling);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, Nudge);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, NudgeWithDataTypes);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest,
-                           NudgeWithDataTypesCoalesced);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, NudgeWithPayloads);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest,
-                           NudgeWithPayloadsCoalesced);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, Throttling);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, AuthInvalid);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, Pause);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, StartWhenNotConnected);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, PauseWhenNotConnected);
-  FRIEND_TEST_ALL_PREFIXES(SyncerThreadWithSyncerTest, StopSyncPermanently);
-  friend class SyncerThreadWithSyncerTest;
-  friend class SyncerThreadFactory;
+class SyncerThread : public sessions::SyncSession::Delegate,
+                     public ServerConnectionEventListener {
  public:
-  // Encapsulates the parameters that make up an interval on which the
-  // syncer thread is sleeping.
+  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();
+
+  typedef Callback0::Type ModeChangeCallback;
+
+  // 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.
+  // If supplied, |callback| will be invoked when the mode has been
+  // changed to |mode| *from the SyncerThread*, and not from the caller
+  // thread.
+  void Start(Mode mode, ModeChangeCallback* callback);
+
+  // 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,
+                     const tracked_objects::Location& nudge_location);
+  void ScheduleNudgeWithPayloads(
+      const base::TimeDelta& delay, NudgeSource source,
+      const syncable::ModelTypePayloadMap& types_with_payloads,
+      const tracked_objects::Location& nudge_location);
+  void ScheduleConfig(const syncable::ModelTypeBitSet& types);
+  void ScheduleClearUserData();
+
+  // 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();
+
+  // ServerConnectionEventListener implementation.
+  // TODO(tim): schedule a nudge when valid connection detected? in 1 minute?
+  virtual void OnServerConnectionEvent(const ServerConnectionEvent2& event);
+
+ private:
+  enum JobProcessDecision {
+    // Indicates we should continue with the current job.
+    CONTINUE,
+    // Indicates that we should save it to be processed later.
+    SAVE,
+    // Indicates we should drop this job.
+    DROP,
+  };
+
+  struct SyncSessionJob {
+    // An enum used to describe jobs for scheduling purposes.
+    enum SyncSessionJobPurpose {
+      // 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,
+      // The user invoked a function in the UI to clear their entire account
+      // and stop syncing (globally).
+      CLEAR_USER_DATA,
+      // 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,
+    };
+    SyncSessionJob();
+    SyncSessionJob(SyncSessionJobPurpose purpose, base::TimeTicks start,
+        linked_ptr<sessions::SyncSession> session, bool is_canary_job,
+        const tracked_objects::Location& nudge_location);
+    ~SyncSessionJob();
+    SyncSessionJobPurpose purpose;
+    base::TimeTicks scheduled_start;
+    linked_ptr<sessions::SyncSession> session;
+    bool is_canary_job;
+
+    // This is the location the nudge came from. used for debugging purpose.
+    // In case of multiple nudges getting coalesced this stores the first nudge
+    // that came in.
+    tracked_objects::Location nudge_location;
+  };
+  friend class SyncerThread2Test;
+  friend class SyncerThread2WhiteboxTest;
+
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest,
+      DropNudgeWhileExponentialBackOff);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest, SaveNudge);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest, ContinueNudge);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest, DropPoll);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest, ContinuePoll);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest, ContinueConfiguration);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest,
+                           SaveConfigurationWhileThrottled);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest,
+                           SaveNudgeWhileThrottled);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest,
+                           ContinueClearUserDataUnderAllCircumstances);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest,
+                           ContinueCanaryJobConfig);
+  FRIEND_TEST_ALL_PREFIXES(SyncerThread2WhiteboxTest,
+      ContinueNudgeWhileExponentialBackOff);
+
+  // 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);
+  };
+
   struct WaitInterval {
     enum Mode {
-      // A wait interval whose duration has not been affected by exponential
-      // backoff.  The base case for exponential backoff falls in to this case
-      // (e.g when the exponent is 1).  So far, we don't need a separate case.
-      // NORMAL intervals are not nudge-rate limited.
-      NORMAL,
       // A wait interval whose duration has been affected by exponential
       // backoff.
       // EXPONENTIAL_BACKOFF intervals are nudge-rate limited to 1 per interval.
@@ -79,286 +180,162 @@ class SyncerThread : public base::RefCountedThreadSafe<SyncerThread>,
       // during such an interval.
       THROTTLED,
     };
+    WaitInterval();
+    ~WaitInterval();
 
     Mode mode;
-    // This bool is set to true if we have observed a nudge during during this
-    // interval and mode == EXPONENTIAL_BACKOFF.
-    bool had_nudge_during_backoff;
-    base::TimeDelta poll_delta;  // The wait duration until the next poll.
 
-    WaitInterval() : mode(NORMAL), had_nudge_during_backoff(false) { }
+    // 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;
+
+    // Configure jobs are saved only when backing off or throttling. So we
+    // expose the pointer here.
+    scoped_ptr<SyncSessionJob> pending_configure_job;
+    WaitInterval(Mode mode, base::TimeDelta length);
   };
 
-  enum NudgeSource {
-    kUnknown = 0,
-    kNotification,
-    kLocal,
-    kContinuation,
-    kClearPrivateData
-  };
-  // Server can overwrite these values via client commands.
-  // Standard short poll. This is used when XMPP is off.
-  static const int kDefaultShortPollIntervalSeconds;
-  // Long poll is used when XMPP is on.
-  static const int kDefaultLongPollIntervalSeconds;
-  // 30 minutes by default. If exponential backoff kicks in, this is the
-  // longest possible poll interval.
-  static const int kDefaultMaxPollIntervalMs;
-  // Maximum interval for exponential backoff.
-  static const int kMaxBackoffSeconds;
-
-  explicit SyncerThread(sessions::SyncSessionContext* context);
-  virtual ~SyncerThread();
+  // Helper to assemble a job and post a delayed task to sync.
+  void ScheduleSyncSessionJob(
+      const base::TimeDelta& delay,
+      SyncSessionJob::SyncSessionJobPurpose purpose,
+      sessions::SyncSession* session,
+      const tracked_objects::Location& nudge_location);
 
-  virtual void WatchConnectionManager(ServerConnectionManager* conn_mgr);
-
-  // Starts a syncer thread.
-  // Returns true if it creates a thread or if there's currently a thread
-  // running and false otherwise.
-  virtual bool Start();
-
-  // Stop processing. |max_wait| doesn't do anything in this version.
-  virtual bool Stop(int max_wait);
-
-  // Request that the thread pauses.  Returns false if the request can
-  // not be completed (e.g. the thread is not running).  When the
-  // thread actually pauses, a SyncEngineEvent::PAUSED event notification
-  // will be sent to the relay channel.
-  virtual bool RequestPause();
-
-  // Request that the thread resumes from pause.  Returns false if the
-  // request can not be completed (e.g. the thread is not running or
-  // is not currently paused).  When the thread actually resumes, a
-  // SyncEngineEvent::RESUMED event notification will be sent to the relay
-  // channel.
-  virtual bool RequestResume();
-
-  // Nudges the syncer to sync with a delay specified. This API is for access
-  // from the SyncerThread's controller and will cause a mutex lock.
-  virtual void NudgeSyncer(int milliseconds_from_now, NudgeSource source);
-
-  // Same as |NudgeSyncer|, but supports tracking the datatypes that caused
-  // the nudge to occur.
-  virtual void NudgeSyncerWithDataTypes(
-      int milliseconds_from_now,
-      NudgeSource source,
-      const syncable::ModelTypeBitSet& model_types);
-
-  // Same as |NudgeSyncer|, but supports including a payload for passing on to
-  // the download updates command. Datatypes with payloads are also considered
-  // to have caused a nudged to occur and treated accordingly.
-  virtual void NudgeSyncerWithPayloads(
-      int milliseconds_from_now,
-      NudgeSource source,
-      const syncable::ModelTypePayloadMap& model_types_with_payloads);
-
-  void SetNotificationsEnabled(bool notifications_enabled);
-
-  // Call this when a directory is opened
-  void CreateSyncer(const std::string& dirname);
-
-  // DDOS avoidance function.  The argument and return value is in seconds
-  static int GetRecommendedDelaySeconds(int base_delay_seconds);
-
- protected:
-  virtual void ThreadMain();
-  void ThreadMainLoop();
-
-  virtual void SetConnected(bool connected);
-
-  virtual void SetSyncerPollingInterval(base::TimeDelta interval);
-  virtual void SetSyncerShortPollInterval(base::TimeDelta interval);
-
-  // Needed to emulate the behavior of pthread_create, which synchronously
-  // started the thread and set the value of thread_running_ to true.
-  // We can't quite match that because we asynchronously post the task,
-  // which opens a window for Stop to get called before the task actually
-  // makes it.  To prevent this, we block Start() until we're sure it's ok.
-  base::WaitableEvent thread_main_started_;
-
-  // Handle of the running thread.
-  base::Thread thread_;
+  // Invoke the Syncer to perform a sync.
+  void DoSyncSessionJob(const SyncSessionJob& job);
 
-  // Fields that are modified / accessed by multiple threads go in this struct
-  // for clarity and explicitness.
-  struct ProtectedFields {
-    ProtectedFields();
-    ~ProtectedFields();
+  // Called after the Syncer has performed the sync represented by |job|, to
+  // reset our state.
+  void FinishSyncSessionJob(const SyncSessionJob& job);
 
-    // False when we want to stop the thread.
-    bool stop_syncer_thread_;
+  // Record important state that might be needed in future syncs, such as which
+  // data types may require cleanup.
+  void UpdateCarryoverSessionState(const SyncSessionJob& old_job);
 
-    // True when a pause was requested.
-    bool pause_requested_;
+  // Helper to FinishSyncSessionJob to schedule the next sync operation.
+  void ScheduleNextSync(const SyncSessionJob& old_job);
 
-    // True when the thread is paused.
-    bool paused_;
+  // Helper to configure polling intervals. Used by Start and ScheduleNextSync.
+  void AdjustPolling(const SyncSessionJob* old_job);
 
-    Syncer* syncer_;
+  // Helper to ScheduleNextSync in case of consecutive sync errors.
+  void HandleConsecutiveContinuationError(const SyncSessionJob& old_job);
 
-    // State of the server connection.
-    bool connected_;
+  // Determines if it is legal to run |job| by checking current
+  // operational mode, backoff or throttling, freshness
+  // (so we don't make redundant syncs), and connection.
+  bool ShouldRunJob(const SyncSessionJob& job);
 
-    // kUnknown if there is no pending nudge.  (Theoretically, there
-    // could be a pending nudge of type kUnknown, so it's better to
-    // check pending_nudge_time_.)
-    NudgeSource pending_nudge_source_;
+  // Decide whether we should CONTINUE, SAVE or DROP the job.
+  JobProcessDecision DecideOnJob(const SyncSessionJob& job);
 
-    // Map of all datatypes that are requesting a nudge. Can be union
-    // from multiple nudges that are coalesced. In addition, we
-    // optionally track a payload associated with each datatype (most recent
-    // payload overwrites old ones). These payloads are used by the download
-    // updates command and can contain datatype specific information the server
-    // might use.
-    syncable::ModelTypePayloadMap pending_nudge_types_;
+  // Decide on whether to CONTINUE, SAVE or DROP the job when we are in
+  // backoff mode.
+  JobProcessDecision DecideWhileInWaitInterval(const SyncSessionJob& job);
 
-    // null iff there is no pending nudge.
-    base::TimeTicks pending_nudge_time_;
+  // Saves the job for future execution. Note: It drops all the poll jobs.
+  void SaveJob(const SyncSessionJob& job);
 
-    // The wait interval for to the current iteration of our main loop.  This is
-    // only written to by the syncer thread, and since the only reader from a
-    // different thread (NudgeSync) is called at totally random times, we don't
-    // really need to access mutually exclusively as the data races that exist
-    // are intrinsic, but do so anyway and avoid using 'volatile'.
-    WaitInterval current_wait_interval_;
-  } vault_;
+  // Coalesces the current job with the pending nudge.
+  void InitOrCoalescePendingJob(const SyncSessionJob& job);
 
-  // Gets signaled whenever a thread outside of the syncer thread changes a
-  // protected field in the vault_.
-  base::ConditionVariable vault_field_changed_;
+  // 'Impl' here refers to real implementation of public functions, running on
+  // |thread_|.
+  void StartImpl(Mode mode, linked_ptr<ModeChangeCallback> callback);
+  void ScheduleNudgeImpl(
+      const base::TimeDelta& delay,
+      sync_pb::GetUpdatesCallerInfo::GetUpdatesSource source,
+      const syncable::ModelTypePayloadMap& types_with_payloads,
+      bool is_canary_job, const tracked_objects::Location& nudge_location);
+  void ScheduleConfigImpl(const ModelSafeRoutingInfo& routing_info,
+      const std::vector<ModelSafeWorker*>& workers,
+      const sync_pb::GetUpdatesCallerInfo::GetUpdatesSource source);
+  void ScheduleClearUserDataImpl();
 
-  // Used to lock everything in |vault_|.
-  base::Lock lock_;
+  // Returns true if the client is currently in exponential backoff.
+  bool IsBackingOff() const;
 
- private:
-  // Threshold multipler for how long before user should be considered idle.
-  static const int kPollBackoffThresholdMultiplier = 10;
+  // Helper to signal all listeners registered with |session_context_|.
+  void Notify(SyncEngineEvent::EventCause cause);
 
-  // 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();
+  // Callback to change backoff state.
+  void DoCanaryJob();
+  void Unthrottle();
 
-  void HandleServerConnectionEvent(const ServerConnectionEvent& event);
-
-  // Collect all local state required for a sync and build a SyncSession out of
-  // it, reset state for the next time, and performs the sync cycle.
-  // See |GetAndResetNudgeSource| for details on what 'reset' means.
-  // |was_nudged| is set to true if the session returned is fulfilling a nudge.
-  // Returns once the session is finished (HasMoreToSync returns false).  The
-  // caller owns the returned SyncSession.
-  sessions::SyncSession* SyncMain(Syncer* syncer,
-                                  bool was_throttled,
-                                  bool continue_sync_cycle,
-                                  bool* initial_sync_for_thread,
-                                  bool* was_nudged);
-
-  // Calculates the next sync wait time and exponential backoff state.
-  // last_poll_wait is the time duration of the previous polling timeout which
-  // was used. user_idle_milliseconds is updated by this method, and is a report
-  // of the full amount of time since the last period of activity for the user.
-  // The continue_sync_cycle parameter is used to determine whether or not we
-  // are calculating a polling wait time that is a continuation of an sync cycle
-  // which terminated while the syncer still had work to do. was_nudged is used
-  // in case of exponential backoff so we only allow one nudge per backoff
-  // interval.
-  WaitInterval CalculatePollingWaitTime(
-      int last_poll_wait,  // in s
-      int* user_idle_milliseconds,
-      bool* continue_sync_cycle,
-      bool was_nudged);
-
-  // Helper to above function, considers effect of user idle time.
-  virtual int CalculateSyncWaitTime(int last_wait, int user_idle_ms);
-
-  // Resets the source tracking state to a clean slate and returns the current
-  // state in a SyncSourceInfo.
-  // The initial sync boolean is updated if read as a sentinel.  The following
-  // two methods work in concert to achieve this goal.
-  // If |was_throttled| was true, this still discards elapsed nudges, but we
-  // treat the request as a periodic poll rather than a nudge from a source.
-  // Builds a SyncSourceInfo and returns whether a nudge occurred in the
-  // |was_nudged| parameter.
-  sessions::SyncSourceInfo GetAndResetNudgeSource(bool was_throttled,
-                                                  bool continue_sync_cycle,
-                                                  bool* initial_sync,
-                                                  bool* was_nudged);
-
-  sessions::SyncSourceInfo MakeSyncSourceInfo(
-      bool nudged,
-      NudgeSource nudge_source,
-      const syncable::ModelTypePayloadMap& model_types_with_payloads,
-      bool* initial_sync);
-
-  int UserIdleTime();
-
-  void WaitUntilConnectedOrQuit();
-
-  // The thread will remain in this method until a resume is requested
-  // or shutdown is started.
-  void PauseUntilResumedOrQuit();
-
-  void EnterPausedState();
-
-  void ExitPausedState();
-
-  // For unit tests only.
-  virtual void DisableIdleDetection();
-
-  // This sets all conditions for syncer thread termination but does not
-  // actually join threads.  It is expected that Stop will be called at some
-  // time after to fully stop and clean up.
-  void RequestSyncerExitAndSetThreadStopConditions();
+  // Executes the pending job. Called whenever an event occurs that may
+  // change conditions permitting a job to run. Like when network connection is
+  // re-established, mode changes etc.
+  void DoPendingJobIfPossible(bool is_canary_job);
 
-  void Notify(SyncEngineEvent::EventCause cause);
+  // The pointer is owned by the caller.
+  browser_sync::sessions::SyncSession* CreateSyncSession(
+      const browser_sync::sessions::SyncSourceInfo& info);
+
+  // Creates a session for a poll and performs the sync.
+  void PollTimerCallback();
+
+  // Assign |start| and |end| to appropriate SyncerStep values for the
+  // specified |purpose|.
+  void SetSyncerStepsForPurpose(SyncSessionJob::SyncSessionJobPurpose purpose,
+                                SyncerStep* start,
+                                SyncerStep* end);
 
-  scoped_ptr<EventListenerHookup> conn_mgr_hookup_;
+  // Initializes the hookup between the ServerConnectionManager and us.
+  void WatchConnectionManager();
+
+  // Used to update |server_connection_ok_|, see below.
+  void CheckServerConnectionManagerStatus(
+      HttpResponse::ServerConnectionCode code);
+
+  // Called once the first time thread_ is started to broadcast an initial
+  // session snapshot containing data like initial_sync_ended.  Important when
+  // the client starts up and does not need to perform an initial sync.
+  void SendInitialSnapshot();
+
+  base::Thread thread_;
 
   // Modifiable versions of kDefaultLongPollIntervalSeconds which can be
   // updated by the server.
-  int syncer_short_poll_interval_seconds_;
-  int syncer_long_poll_interval_seconds_;
-
-  // The time we wait between polls in seconds. This is used as lower bound on
-  // our wait time. Updated once per loop from the command line flag.
-  int syncer_polling_interval_;
-
-  // The upper bound on the nominal wait between polls in seconds. Note that
-  // this bounds the "nominal" poll interval, while the the actual interval
-  // also takes previous failures into account.
-  int syncer_max_interval_;
-
-  // This causes syncer to start syncing ASAP. If the rate of requests is too
-  // high the request will be silently dropped.  mutex_ should be held when
-  // this is called.
-  void NudgeSyncImpl(
-      int milliseconds_from_now,
-      NudgeSource source,
-      const syncable::ModelTypePayloadMap& model_types_with_payloads);
-
-#if defined(OS_LINUX)
-  // On Linux, we need this information in order to query idle time.
-  scoped_ptr<IdleQueryLinux> idle_query_;
-#endif
+  base::TimeDelta syncer_short_poll_interval_seconds_;
+  base::TimeDelta syncer_long_poll_interval_seconds_;
 
-  scoped_ptr<sessions::SyncSessionContext> session_context_;
+  // 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_;
 
-  // Set whenever the server instructs us to stop sending it requests until
-  // a specified time, and reset for each call to SyncShare. (Note that the
-  // WaitInterval::THROTTLED contract is such that we don't call SyncShare at
-  // all until the "silenced until" embargo expires.)
-  base::TimeTicks silenced_until_;
+  // Have we observed a valid server connection?
+  bool server_connection_ok_;
 
-  // Useful for unit tests
-  bool disable_idle_detection_;
+  // 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);
 };
 
+
 }  // namespace browser_sync
 
+// 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(browser_sync::SyncerThread);
+
 #endif  // CHROME_BROWSER_SYNC_ENGINE_SYNCER_THREAD_H_