src/IO/FileTransaction.hpp

   1 /*
   2 Copyright_License {
   3
   4   XCSoar Glide Computer - http://www.xcsoar.org/
   5   Copyright (C) 2000-2013 The XCSoar Project
   6   A detailed list of copyright holders can be found in the file "AUTHORS".
   7
   8   This program is free software; you can redistribute it and/or
   9   modify it under the terms of the GNU General Public License
  10   as published by the Free Software Foundation; either version 2
  11   of the License, or (at your option) any later version.
  12
  13   This program is distributed in the hope that it will be useful,
  14   but WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16   GNU General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with this program; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  21 }
  22 */
  23
  24 #ifndef XCSOAR_FILE_TRANSACTION_HPP
  25 #define XCSOAR_FILE_TRANSACTION_HPP
  26
  27 #include "Util/StaticString.hpp"
  28 #include "Compiler.h"
  29
  30 #include <windef.h> /* for MAX_PATH */
  31 #include <tchar.h>
  32
  33 /**
  34  * Write to a temporary file, and then replace the old file
  35  * atomically.  If something fails in between, the old file remains in
  36  * place (or none, if it doesn't exist previously).
  37  *
  38  * To use this class, create an instance and write to the file
  39  * specified by GetTemporaryPath().  After the file is finished, call
  40  * Commit().  The destructor will automatically delete the temporary
  41  * file if you decide not to call Commit().
  42  */
  43 class FileTransaction {
  44   StaticString<MAX_PATH> final_path;
  45   StaticString<MAX_PATH> temporary_path;
  46
  47 public:
  48   FileTransaction(const TCHAR *_path);
  49
  50   /**
  51    * The destructor auto-rolls back the transaction (i.e. deletes the
  52    * temporary file) unless Commit() has been called.
  53    */
  54   ~FileTransaction();
  55
  56   /**
  57    * Returns the temporary path.  This is the path that shall be used
  58    * by the caller to write the file.
  59    */
  60   const TCHAR *GetTemporaryPath() const {
  61     return temporary_path.c_str();
  62   }
  63
  64   /**
  65    * Replace the file with the contents of the temporary file.
  66    *
  67    * @return true on success
  68    */
  69   bool Commit();
  70
  71   /**
  72    * Abandon the transaction, i.e. close it, but don't clean up the
  73    * temporary file.
  74    */
  75   void Abandon();
  76 };
  77
  78 #endif