Move ImportantFileWriter to base/. It now has two consumers, base/prefs and chrome/.

chrome/common/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 CHROME_COMMON_IMPORTANT_FILE_WRITER_H_
-#define CHROME_COMMON_IMPORTANT_FILE_WRITER_H_
-
-#include <string>
-
-#include "base/basictypes.h"
-#include "base/file_path.h"
-#include "base/memory/ref_counted.h"
-#include "base/threading/non_thread_safe.h"
-#include "base/time.h"
-#include "base/timer.h"
-
-namespace base {
-class MessageLoopProxy;
-class Thread;
-}
-
-// Helper to ensure that a file won't be corrupted by the write (for example on
-// application crash). Consider a naive way to save an important file F:
-//
-// 1. Open F for writing, truncating it.
-// 2. Write new data to F.
-//
-// It's good when it works, but it gets very bad if step 2. doesn't complete.
-// It can be caused by a crash, a computer hang, or a weird I/O error. And you
-// 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 ImportantFileWriter : public base::NonThreadSafe {
- public:
-  // Used by ScheduleSave to lazily provide the data to be saved. Allows us
-  // to also batch data serializations.
-  class 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() {}
-  };
-
-  // Initialize the writer.
-  // |path| is the name of file to write.
-  // |file_message_loop_proxy| is the MessageLoopProxy for a thread on which
-  // file I/O can be done.
-  // All non-const methods, ctor and dtor must be called on the same thread.
-  ImportantFileWriter(const FilePath& path,
-                      base::MessageLoopProxy* file_message_loop_proxy);
-
-  // You have to ensure that there are no pending writes at the moment
-  // of destruction.
-  ~ImportantFileWriter();
-
-  const FilePath& path() const { return path_; }
-
-  // Returns true if there is a scheduled write pending which has not yet
-  // been started.
-  bool HasPendingWrite() const;
-
-  // Save |data| to target filename. Does not block. If there is a pending write
-  // scheduled by ScheduleWrite, it is cancelled.
-  void WriteNow(const std::string& data);
-
-  // 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);
-
-  // Serialize data pending to be saved and execute write on backend thread.
-  void DoScheduledWrite();
-
-  base::TimeDelta commit_interval() const {
-    return commit_interval_;
-  }
-
-  void set_commit_interval(const base::TimeDelta& interval) {
-    commit_interval_ = interval;
-  }
-
- private:
-  // Path being written to.
-  const FilePath path_;
-
-  // MessageLoopProxy for the thread on which file I/O can be done.
-  scoped_refptr<base::MessageLoopProxy> file_message_loop_proxy_;
-
-  // Timer used to schedule commit after ScheduleWrite.
-  base::OneShotTimer<ImportantFileWriter> timer_;
-
-  // Serializer which will provide the data to be saved.
-  DataSerializer* serializer_;
-
-  // Time delta after which scheduled data will be written to disk.
-  base::TimeDelta commit_interval_;
-
-  DISALLOW_COPY_AND_ASSIGN(ImportantFileWriter);
-};
-
-#endif  // CHROME_COMMON_IMPORTANT_FILE_WRITER_H_