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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 | |
13 namespace 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. | |
30 class 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_ | |
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