src/FileLock.h

   1 //
   2 // This file is part of the aMule Project.
   3 //
   4 // Copyright (c) 2006-2008 Mikkel Schubert ( xaignar@users.sourceforge.net )
   5 // Copyright (c) 2006-2008 aMule Team ( admin@amule.org / http://www.amule.org )
   6 //
   7 // Any parts of this program derived from the xMule, lMule or eMule project,
   8 // or contributed by third-party developers are copyrighted by their
   9 // respective authors.
  10 //
  11 // This program is free software; you can redistribute it and/or modify
  12 // it under the terms of the GNU General Public License as published by
  13 // the Free Software Foundation; either version 2 of the License, or
  14 // (at your option) any later version.
  15 //
  16 // This program is distributed in the hope that it will be useful,
  17 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 // GNU General Public License for more details.
  20 //
  21 // You should have received a copy of the GNU General Public License
  22 // along with this program; if not, write to the Free Software
  23 // Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA
  24 //
  25
  26 #ifndef FILELOCK_H
  27 #define FILELOCK_H
  28
  29 #include <fcntl.h>
  30 #include <cerrno>
  31 #ifndef _MSC_VER
  32 #include <unistd.h> // Do_not_auto_remove (Needed for OpenBSD)
  33 #endif
  34 #include <string> // Do_not_auto_remove (g++-4.0.1 except win32)
  35
  36
  37 /**
  38  * This class provides an easy way to lock non-critical
  39  * files used by multiple applications. However, since
  40  * the implementation relies on fcntl, it may not work
  41  * on all filesystems (NFS) and thus locking is not
  42  * certain.
  43  *
  44  * Currently, this lock holds an exclusive lock on the
  45  * file in question. It is assumed that the file will
  46  * be read/written by all users.
  47  *
  48  */
  49 class CFileLock
  50 {
  51 public:
  52         /**
  53          * Locks the lock-file for the specified file.
  54          *
  55          * The lock-file is a file named file + "_lock", and
  56          * will be created if it does not already exist. This
  57          * file is not removed afterwards.
  58          */
  59         CFileLock(const std::string& file)
  60 #if defined(__WIN32__) || defined(_MSC_VER)
  61         {
  62         }
  63 #else
  64                 : m_fd(-1),
  65                   m_ok(false)
  66         {
  67                 // File must be open with O_WRONLY to be able to set write-locks.
  68                 m_fd = ::open((file + "_lock").c_str(), O_CREAT | O_WRONLY, 0600);
  69                 if (m_fd != -1) {
  70                         m_ok = SetLock(true);
  71                 }
  72         }
  73
  74         /** Releases the lock, if any is held. */
  75         ~CFileLock() {
  76                 if (m_ok) {
  77                         SetLock(false);
  78                 }
  79
  80                 if (m_fd != -1) {
  81                         close(m_fd);
  82                 }
  83         }
  84
  85 private:
  86         //! Not copyable.
  87         CFileLock(const CFileLock&);
  88         //! Not assignable.
  89         CFileLock& operator=(const CFileLock&);
  90
  91         /** Locks or unlocks the lock-file, returning true on success. */
  92         bool SetLock(bool doLock) {
  93                 struct flock lock;
  94                 lock.l_type = (doLock ? F_WRLCK : F_UNLCK);
  95
  96                 // Lock the entire file
  97                 lock.l_whence = SEEK_SET;
  98                 lock.l_start = 0;
  99                 lock.l_len = 0;
 100
 101                 // Keep trying if interrupted by a signal.
 102                 while (true) {
 103                         if (fcntl(m_fd, F_SETLKW, &lock) == 0) {
 104                                 return true;
 105                         } else if ((errno != EACCES) and (errno != EAGAIN) and (errno != EINTR)) {
 106                                 // Not an error we can recover from.
 107                                 break;
 108                         }
 109                 }
 110
 111                 return false;
 112         }
 113
 114
 115         //! Desribtor of the file being locked.
 116         int m_fd;
 117
 118         //! Specifies if the file-lock was aquired.
 119         bool m_ok;
 120 #endif
 121 };
 122
 123 #endif
 124 // File_checked_for_headers