1 // Copyright 2011 The Chromium Authors 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 <stdint.h> 11 12 #include "base/memory/raw_ptr.h" 13 #include "net/base/net_export.h" 14 #include "net/disk_cache/blockfile/disk_format_base.h" 15 16 namespace disk_cache { 17 18 // This class implements a file lock that lives on the header of a memory mapped 19 // file. This is NOT a thread related lock, it is a lock to detect corruption 20 // of the file when the process crashes in the middle of an update. 21 // The lock is acquired on the constructor and released on the destructor. 22 // The typical use of the class is: 23 // { 24 // BlockFileHeader* header = GetFileHeader(); 25 // FileLock lock(header); 26 // header->max_entries = num_entries; 27 // // At this point the destructor is going to release the lock. 28 // } 29 // It is important to perform Lock() and Unlock() operations in the right order, 30 // because otherwise the desired effect of the "lock" will not be achieved. If 31 // the operations are inlined / optimized, the "locked" operations can happen 32 // outside the lock. 33 class NET_EXPORT_PRIVATE FileLock { 34 public: 35 explicit FileLock(BlockFileHeader* header); 36 virtual ~FileLock(); 37 38 // Virtual to make sure the compiler never inlines the calls. 39 virtual void Lock(); 40 virtual void Unlock(); 41 private: 42 bool acquired_; 43 raw_ptr<volatile int32_t> updating_; 44 }; 45 46 } // namespace disk_cache 47 48 #endif // NET_DISK_CACHE_BLOCKFILE_FILE_LOCK_H_ 49