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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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