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48 lines
1.6 KiB
C++
48 lines
1.6 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// See net/disk_cache/disk_cache.h for the public interface of the cache.
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#ifndef NET_DISK_CACHE_BLOCKFILE_FILE_LOCK_H_
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#define NET_DISK_CACHE_BLOCKFILE_FILE_LOCK_H_
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#include <stdint.h>
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#include "net/base/net_export.h"
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#include "net/disk_cache/blockfile/disk_format_base.h"
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namespace disk_cache {
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// This class implements a file lock that lives on the header of a memory mapped
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// file. This is NOT a thread related lock, it is a lock to detect corruption
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// of the file when the process crashes in the middle of an update.
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// The lock is acquired on the constructor and released on the destructor.
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// The typical use of the class is:
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// {
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// BlockFileHeader* header = GetFileHeader();
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// FileLock lock(header);
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// header->max_entries = num_entries;
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// // At this point the destructor is going to release the lock.
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// }
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// It is important to perform Lock() and Unlock() operations in the right order,
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// because otherwise the desired effect of the "lock" will not be achieved. If
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// the operations are inlined / optimized, the "locked" operations can happen
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// outside the lock.
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class NET_EXPORT_PRIVATE FileLock {
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public:
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explicit FileLock(BlockFileHeader* header);
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virtual ~FileLock();
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// Virtual to make sure the compiler never inlines the calls.
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virtual void Lock();
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virtual void Unlock();
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private:
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bool acquired_;
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volatile int32_t* updating_;
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};
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} // namespace disk_cache
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#endif // NET_DISK_CACHE_BLOCKFILE_FILE_LOCK_H_
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