1// Copyright (c) 2011 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// See net/disk_cache/disk_cache.h for the public interface of the cache.
6
7#ifndef NET_DISK_CACHE_BLOCKFILE_FILE_LOCK_H_
8#define NET_DISK_CACHE_BLOCKFILE_FILE_LOCK_H_
9
10#include "net/base/net_export.h"
11#include "net/disk_cache/blockfile/disk_format_base.h"
12
13namespace disk_cache {
14
15// This class implements a file lock that lives on the header of a memory mapped
16// file. This is NOT a thread related lock, it is a lock to detect corruption
17// of the file when the process crashes in the middle of an update.
18// The lock is acquired on the constructor and released on the destructor.
19// The typical use of the class is:
20//    {
21//      BlockFileHeader* header = GetFileHeader();
22//      FileLock lock(header);
23//      header->max_entries = num_entries;
24//      // At this point the destructor is going to release the lock.
25//    }
26// It is important to perform Lock() and Unlock() operations in the right order,
27// because otherwise the desired effect of the "lock" will not be achieved. If
28// the operations are inlined / optimized, the "locked" operations can happen
29// outside the lock.
30class NET_EXPORT_PRIVATE FileLock {
31 public:
32  explicit FileLock(BlockFileHeader* header);
33  virtual ~FileLock();
34
35  // Virtual to make sure the compiler never inlines the calls.
36  virtual void Lock();
37  virtual void Unlock();
38 private:
39  bool acquired_;
40  volatile int32* updating_;
41};
42
43}  // namespace disk_cache
44
45#endif  // NET_DISK_CACHE_BLOCKFILE_FILE_LOCK_H_
46