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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef COMPONENTS_SYNC_DRIVER_CHANGE_PROCESSOR_H_
      6 #define COMPONENTS_SYNC_DRIVER_CHANGE_PROCESSOR_H_
      7 
      8 #include "components/sync_driver/data_type_error_handler.h"
      9 #include "sync/internal_api/public/base_transaction.h"
     10 #include "sync/internal_api/public/change_record.h"
     11 #include "sync/internal_api/public/user_share.h"
     12 
     13 namespace syncer {
     14 class UnrecoverableErrorHandler;
     15 }  // namespace syncer
     16 
     17 namespace browser_sync {
     18 
     19 class ModelAssociator;
     20 
     21 // An interface used to apply changes from the sync model to the browser's
     22 // native model.  This does not currently distinguish between model data types.
     23 class ChangeProcessor {
     24  public:
     25   explicit ChangeProcessor(DataTypeErrorHandler* error_handler);
     26   virtual ~ChangeProcessor();
     27 
     28   // Call when the processor should accept changes from either provided model
     29   // and apply them to the other.  Both the native model and sync_api are
     30   // expected to be initialized and loaded.  You must have set a valid
     31   // ModelAssociator and UnrecoverableErrorHandler before using this method, and
     32   // the two models should be associated w.r.t the ModelAssociator provided.
     33   void Start(syncer::UserShare* share_handle);
     34 
     35   // Changes have been applied to the backend model and are ready to be
     36   // applied to the frontend model.
     37   virtual void ApplyChangesFromSyncModel(
     38       const syncer::BaseTransaction* trans,
     39       int64 model_version,
     40       const syncer::ImmutableChangeRecordList& changes) = 0;
     41 
     42   // The changes found in ApplyChangesFromSyncModel may be too slow to be
     43   // performed while holding a [Read/Write]Transaction lock or may interact
     44   // with another thread, which might itself be waiting on the transaction lock,
     45   // putting us at risk of deadlock.
     46   // This function is called once the transactional lock is released and it is
     47   // safe to perform inter-thread or slow I/O operations. Note that not all
     48   // datatypes need this, so we provide an empty default version.
     49   virtual void CommitChangesFromSyncModel();
     50 
     51   // This ensures that startobserving gets called after stopobserving even
     52   // if there is an early return in the function.
     53   template <class T>
     54   class ScopedStopObserving {
     55    public:
     56     explicit ScopedStopObserving(T* processor)
     57         : processor_(processor) {
     58       processor_->StopObserving();
     59     }
     60     ~ScopedStopObserving() {
     61       processor_->StartObserving();
     62     }
     63 
     64    private:
     65     ScopedStopObserving() {}
     66     T* processor_;
     67   };
     68 
     69  protected:
     70   // These methods are invoked by Start() and Stop() to do
     71   // implementation-specific work.
     72   virtual void StartImpl() = 0;
     73 
     74   DataTypeErrorHandler* error_handler() const;
     75   virtual syncer::UserShare* share_handle() const;
     76 
     77  private:
     78   DataTypeErrorHandler* error_handler_;  // Guaranteed to outlive us.
     79 
     80   // The sync model we are processing changes from.
     81   syncer::UserShare* share_handle_;
     82 
     83   DISALLOW_COPY_AND_ASSIGN(ChangeProcessor);
     84 };
     85 
     86 }  // namespace browser_sync
     87 
     88 #endif  // COMPONENTS_SYNC_DRIVER_CHANGE_PROCESSOR_H_
     89