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_ 46