Implement lossy pref behavior for JsonPrefStore.

base/files/important_file_writer.h

 // Copyright (c) 2012 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 BASE_FILES_IMPORTANT_FILE_WRITER_H_
 #define BASE_FILES_IMPORTANT_FILE_WRITER_H_
 
 #include <string>
 
 #include "base/base_export.h"
@@ skipping 21 matching lines @@
 // end up with a broken file.
 //
 // To be safe, we don't start with writing directly to F. Instead, we write to
 // to a temporary file. Only after that write is successful, we rename the
 // temporary file to target filename.
 //
 // If you want to know more about this approach and ext3/ext4 fsync issues, see
 // http://valhenson.livejournal.com/37921.html
 class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
  public:
-  // Used by ScheduleSave to lazily provide the data to be saved. Allows us
-  // to also batch data serializations.
+  // Used to lazily provide the data to be saved. Allows us to also batch data
+  // serializations.
   class BASE_EXPORT DataSerializer {
    public:
     // Should put serialized string in |data| and return true on successful
     // serialization. Will be called on the same thread on which
     // ImportantFileWriter has been created.
     virtual bool SerializeData(std::string* data) = 0;
 
    protected:
     virtual ~DataSerializer() {}
   };
 
-  // Save |data| to |path| in an atomic manner (see the class comment above).
-  // Blocks and writes data on the current thread.
-  static bool WriteFileAtomically(const FilePath& path,
-                                  const std::string& data);
-
-  // Initialize the writer.
-  // |path| is the name of file to write.
-  // |task_runner| is the SequencedTaskRunner instance where on which we will
-  // execute file I/O operations.
-  // All non-const methods, ctor and dtor must be called on the same thread.
-  ImportantFileWriter(
-      const FilePath& path,
-      const scoped_refptr<base::SequencedTaskRunner>& task_runner);
-
-  // You have to ensure that there are no pending writes at the moment
-  // of destruction.
-  ~ImportantFileWriter();
-
-  const FilePath& path() const { return path_; }
+  virtual ~ImportantFileWriter() {}
 
   // Returns true if there is a scheduled write pending which has not yet
   // been started.
-  bool HasPendingWrite() const;
+  virtual bool HasPendingWrite() const = 0;
 
   // Save |data| to target filename. Does not block. If there is a pending write
   // scheduled by ScheduleWrite, it is cancelled.
-  void WriteNow(scoped_ptr<std::string> data);
+  virtual void WriteNow(scoped_ptr<std::string> data) = 0;
 
   // Schedule a save to target filename. Data will be serialized and saved
   // to disk after the commit interval. If another ScheduleWrite is issued
   // before that, only one serialization and write to disk will happen, and
   // the most recent |serializer| will be used. This operation does not block.
   // |serializer| should remain valid through the lifetime of
   // ImportantFileWriter.
-  void ScheduleWrite(DataSerializer* serializer);
+  virtual void ScheduleWrite(DataSerializer* serializer) = 0;
 
   // Serialize data pending to be saved and execute write on backend thread.
-  void DoScheduledWrite();
+  virtual void DoScheduledWrite() = 0;
 
   // Registers |on_next_successful_write| to be called once, on the next
   // successful write event. Only one callback can be set at once.
+  virtual void RegisterOnNextSuccessfulWriteCallback(
+      const base::Closure& on_next_successful_write) = 0;
+
+  // Returns the time delta after which scheduled data will be written to disk.
+  virtual TimeDelta CommitInterval() const = 0;
+};
+
+class BASE_EXPORT ImportantFileWriterImpl : public ImportantFileWriter {
+ public:
+  // Save |data| to |path| in an atomic manner (see the class comment above).
+  // Blocks and writes data on the current thread.
+  static bool WriteFileAtomically(const FilePath& path,
+                                  const std::string& data);
+
+  // Initialize the writer.
+  // |path| is the name of file to write.
+  // |task_runner| is the SequencedTaskRunner instance where on which we will
+  // execute file I/O operations.
+  // All non-const methods, ctor and dtor must be called on the same thread.
+  ImportantFileWriterImpl(
+      const FilePath& path,
+      const scoped_refptr<base::SequencedTaskRunner>& task_runner);
+
+  // You have to ensure that there are no pending writes at the moment
+  // of destruction.
+  ~ImportantFileWriterImpl() override;
+
+  const FilePath& path() const { return path_; }
+
+  // ImportantFileWriter overrides.
+  bool HasPendingWrite() const override;
+  void WriteNow(scoped_ptr<std::string> data) override;
+  void ScheduleWrite(DataSerializer* serializer) override;
+  void DoScheduledWrite() override;
   void RegisterOnNextSuccessfulWriteCallback(
-      const base::Closure& on_next_successful_write);
-
-  TimeDelta commit_interval() const {
-    return commit_interval_;
-  }
+      const base::Closure& on_next_successful_write) override;
+  TimeDelta CommitInterval() const override;
 
   void set_commit_interval(const TimeDelta& interval) {
     commit_interval_ = interval;
   }
 
  private:
   // Helper method for WriteNow().
   bool PostWriteTask(const Callback<bool()>& task);
 
   // If |result| is true and |on_next_successful_write_| is set, invokes
   // |on_successful_write_| and then resets it; no-ops otherwise.
   void ForwardSuccessfulWrite(bool result);
 
   // Invoked once and then reset on the next successful write event.
   base::Closure on_next_successful_write_;
 
   // Path being written to.
   const FilePath path_;
 
   // TaskRunner for the thread on which file I/O can be done.
   const scoped_refptr<base::SequencedTaskRunner> task_runner_;
 
   // Timer used to schedule commit after ScheduleWrite.
-  OneShotTimer<ImportantFileWriter> timer_;
+  OneShotTimer<ImportantFileWriterImpl> timer_;
 
   // Serializer which will provide the data to be saved.
   DataSerializer* serializer_;
 
   // Time delta after which scheduled data will be written to disk.
   TimeDelta commit_interval_;
 
-  WeakPtrFactory<ImportantFileWriter> weak_factory_;
+  WeakPtrFactory<ImportantFileWriterImpl> weak_factory_;
 
-  DISALLOW_COPY_AND_ASSIGN(ImportantFileWriter);
+  DISALLOW_COPY_AND_ASSIGN(ImportantFileWriterImpl);
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_IMPORTANT_FILE_WRITER_H_