[Sync] Make syncer commands avoid posting tasks on threads with no work to do

chrome/browser/sync/sessions/sync_session.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 representing an attempt to synchronize the local syncable data
 // store with a sync server. A SyncSession instance is passed as a stateful
 // bundle to and from various SyncerCommands with the goal of converging the
 // client view of data with that of the server. The commands twiddle with
 // session status in response to events and hiccups along the way, set and
 // query session progress with regards to conflict resolution and applying
 // server updates, and access the SyncSessionContext for the current session
 // via SyncSession instances.
 
 #ifndef CHROME_BROWSER_SYNC_SESSIONS_SYNC_SESSION_H_
 #define CHROME_BROWSER_SYNC_SESSIONS_SYNC_SESSION_H_
 #pragma once
 
 #include <map>
+#include <set>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time.h"
 #include "chrome/browser/sync/engine/model_safe_worker.h"
 #include "chrome/browser/sync/sessions/ordered_commit_set.h"
 #include "chrome/browser/sync/sessions/session_state.h"
@@ skipping 83 matching lines @@
   // with corresponding state in |this|, leaving |s| unchanged.  Allows |this|
   // to take on the responsibilities |s| had (e.g. certain data types) in the
   // next SyncShare operation using |this|, rather than needed two separate
   // sessions.
   void Coalesce(const SyncSession& session);
 
   // Compares the routing_info_, workers and payload map with the passed in
   // session. Purges types from the above 3 which are not in session. Useful
   // to update the sync session when the user has disabled some types from
   // syncing.
-  void RebaseRoutingInfoWithLatest(SyncSession* session);
+  void RebaseRoutingInfoWithLatest(const SyncSession& session);
 
   // Should be called any time |this| is being re-used in a new call to
   // SyncShare (e.g., HasMoreToSync returned true).
   void ResetTransientState();
 
   // TODO(akalin): Split this into context() and mutable_context().
   SyncSessionContext* context() const { return context_; }
   Delegate* delegate() const { return delegate_; }
   syncable::WriteTransaction* write_transaction() { return write_transaction_; }
   const StatusController& status_controller() const {
@@ skipping 12 matching lines @@
 
   // Volatile reader for the source member of the sync session object.  The
   // value is set to the SYNC_CYCLE_CONTINUATION value to signal that it has
   // been read.
   SyncSourceInfo TestAndSetSource();
 
   const std::vector<ModelSafeWorker*>& workers() const { return workers_; }
   const ModelSafeRoutingInfo& routing_info() const { return routing_info_; }
   const SyncSourceInfo& source() const { return source_; }
 
+  // Returns the set of groups which have enabled types.
+  const std::set<ModelSafeGroup>& GetEnabledGroups() const;
+
+  // Returns the set of enabled groups that have conflicts.
+  std::set<ModelSafeGroup> GetEnabledGroupsWithConflicts() const;
+
  private:
   // Extend the encapsulation boundary to utilities for internal member
   // assignments. This way, the scope of these actions is explicit, they can't
   // be overridden, and assigning is always accompanied by unassigning.
   friend class ScopedSetSessionWriteTransaction;
 
   // The context for this session, guaranteed to outlive |this|.
   SyncSessionContext* const context_;
 
   // The source for initiating this sync session.
   SyncSourceInfo source_;
 
   // Information about extensions activity since the last successful commit.
   ExtensionsActivityMonitor::Records extensions_activity_;
 
   // Used to allow various steps to share a transaction. Can be NULL.
   syncable::WriteTransaction* write_transaction_;
 
   // The delegate for this session, must never be NULL.
-  Delegate* delegate_;
+  Delegate* const delegate_;
 
   // Our controller for various status and error counters.
   scoped_ptr<StatusController> status_controller_;
 
   // The set of active ModelSafeWorkers for the duration of this session.
   // This can change if this session is Coalesce()'d with another.
   std::vector<ModelSafeWorker*> workers_;
 
   // The routing info for the duration of this session, dictating which
   // datatypes should be synced and which workers should be used when working
   // on those datatypes.
   ModelSafeRoutingInfo routing_info_;
 
+  // The set of groups with enabled types.  Computed from
+  // |routing_info_|.
+  std::set<ModelSafeGroup> enabled_groups_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncSession);
 };
 
 // Installs a WriteTransaction to a given session and later clears it when the
 // utility falls out of scope. Transactions are not nestable, so it is an error
 // to try and use one of these if the session already has a transaction.
 class ScopedSetSessionWriteTransaction {
  public:
   ScopedSetSessionWriteTransaction(SyncSession* session,
                                    syncable::WriteTransaction* trans)
       : session_(session) {
     DCHECK(!session_->write_transaction_);
     session_->write_transaction_ = trans;
   }
   ~ScopedSetSessionWriteTransaction() { session_->write_transaction_ = NULL; }
 
  private:
   SyncSession* session_;
   DISALLOW_COPY_AND_ASSIGN(ScopedSetSessionWriteTransaction);
 };
 
 }  // namespace sessions
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_SESSIONS_SYNC_SESSION_H_