Refactor preference syncing.

chrome/browser/sync/glue/change_processor.h

-// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
+// 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.
 
 #ifndef CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_
 #define CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_
 #pragma once
 
 #include "chrome/browser/sync/engine/syncapi.h"
 #include "chrome/browser/sync/glue/sync_backend_host.h"
 
 class Profile;
 
 namespace browser_sync {
 
 class ModelAssociator;
 class UnrecoverableErrorHandler;
 
 // An interface used to apply changes from the sync model to the browser's
 // native model.  This does not currently distinguish between model data types.
 class ChangeProcessor {
  public:
-  explicit ChangeProcessor(UnrecoverableErrorHandler* error_handler)
-      : running_(false), error_handler_(error_handler), share_handle_(NULL) {}
+  explicit ChangeProcessor(UnrecoverableErrorHandler* error_handler);
   virtual ~ChangeProcessor();
 
   // Call when the processor should accept changes from either provided model
   // and apply them to the other.  Both the chrome model and sync_api are
   // expected to be initialized and loaded.  You must have set a valid
   // ModelAssociator and UnrecoverableErrorHandler before using this method,
   // and the two models should be associated w.r.t the ModelAssociator provided.
   // It is safe to call Start again after previously Stop()ing the processor.
   // Subclasses can extract their associated chrome model from |profile| in
   // |StartImpl|.
   void Start(Profile* profile, sync_api::UserShare* share_handle);
   void Stop();
   virtual bool IsRunning() const;
 
   // Changes have been applied to the backend model and are ready to be
   // applied to the frontend model. See syncapi.h for detailed instructions on
   // how to interpret and process |changes|.
   virtual void ApplyChangesFromSyncModel(
       const sync_api::BaseTransaction* trans,
       const sync_api::SyncManager::ChangeRecord* changes,
       int change_count) = 0;
 
   // The changes found in ApplyChangesFromSyncModel may be too slow to be
-  // performed while holding a [Read/Write]Transaction lock. This function
-  // is called once the lock is released and performs any slow I/O operations
-  // without unnecessarily slowing the UI. Note that not all datatypes need
-  // this, so we provide an empty default version.
-  virtual void CommitChangesFromSyncModel() { }
+  // performed while holding a [Read/Write]Transaction lock or may interact
+  // with another thread, which might itself be waiting on the transaction lock,
+  // putting us at risk of deadlock.
+  // This function is called once the transactional lock is released and it is
+  // safe to perform inter-thread or slow I/O operations. Note that not all
+  // datatypes need this, so we provide an empty default version.
+  virtual void CommitChangesFromSyncModel();
 
  protected:
   // These methods are invoked by Start() and Stop() to do
   // implementation-specific work.
   virtual void StartImpl(Profile* profile) = 0;
   virtual void StopImpl() = 0;
 
   bool running() { return running_; }
-  UnrecoverableErrorHandler* error_handler() { return error_handler_; }
-  sync_api::UserShare* share_handle() { return share_handle_; }
+  UnrecoverableErrorHandler* error_handler();
+  sync_api::UserShare* share_handle();
 
  private:
   bool running_;  // True if we have been told it is safe to process changes.
   UnrecoverableErrorHandler* error_handler_;  // Guaranteed to outlive us.
 
   // The sync model we are processing changes from. Non-NULL when |running_| is
   // true.
   sync_api::UserShare* share_handle_;
 
   DISALLOW_COPY_AND_ASSIGN(ChangeProcessor);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_