1/*
2 *  Copyright 2009 The WebRTC Project Authors. All rights reserved.
3 *
4 *  Use of this source code is governed by a BSD-style license
5 *  that can be found in the LICENSE file in the root of the source
6 *  tree. An additional intellectual property rights grant can be found
7 *  in the file PATENTS.  All contributing project authors may
8 *  be found in the AUTHORS file in the root of the source tree.
9 */
10
11#ifndef WEBRTC_BASE_FILELOCK_H_
12#define WEBRTC_BASE_FILELOCK_H_
13
14#include <string>
15
16#include "webrtc/base/constructormagic.h"
17#include "webrtc/base/scoped_ptr.h"
18
19namespace rtc {
20
21class FileStream;
22
23// Implements a very simple cross process lock based on a file.
24// When Lock(...) is called we try to open/create the file in read/write
25// mode without any sharing. (Or locking it with flock(...) on Unix)
26// If the process crash the OS will make sure that the file descriptor
27// is released and another process can accuire the lock.
28// This doesn't work on ancient OSX/Linux versions if used on NFS.
29// (Nfs-client before: ~2.6 and Linux Kernel < 2.6.)
30class FileLock {
31 public:
32  virtual ~FileLock();
33
34  // Attempts to lock the file. The caller owns the returned
35  // lock object. Returns NULL if the file already was locked.
36  static FileLock* TryLock(const std::string& path);
37  void Unlock();
38
39 protected:
40  FileLock(const std::string& path, FileStream* file);
41
42 private:
43  void MaybeUnlock();
44
45  std::string path_;
46  scoped_ptr<FileStream> file_;
47
48  DISALLOW_EVIL_CONSTRUCTORS(FileLock);
49};
50
51}  // namespace rtc
52
53#endif  // WEBRTC_BASE_FILELOCK_H_
54