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1 // Copyright (c) 2012 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 #include "net/disk_cache/blockfile/file_lock.h"
6 
7 #include "base/atomicops.h"
8 
9 namespace {
10 
Barrier()11 void Barrier() {
12 #if !defined(COMPILER_MSVC)
13   // VS uses memory barrier semantics for volatiles.
14   base::subtle::MemoryBarrier();
15 #endif
16 }
17 
18 }  // namespace
19 
20 namespace disk_cache {
21 
FileLock(BlockFileHeader * header)22 FileLock::FileLock(BlockFileHeader* header) {
23   updating_ = &header->updating;
24   (*updating_)++;
25   Barrier();
26   acquired_ = true;
27 }
28 
~FileLock()29 FileLock::~FileLock() {
30   Unlock();
31 }
32 
Lock()33 void FileLock::Lock() {
34   if (acquired_)
35     return;
36   (*updating_)++;
37   Barrier();
38 }
39 
Unlock()40 void FileLock::Unlock() {
41   if (!acquired_)
42     return;
43   Barrier();
44   (*updating_)--;
45 }
46 
47 }  // namespace disk_cache
48