net/disk_cache/blockfile/file_lock.cc

   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
  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
  22 FileLock::FileLock(BlockFileHeader* header) {
  23   updating_ = &header->updating;
  24   (*updating_)++;
  25   Barrier();
  26   acquired_ = true;
  27 }
  28
  29 FileLock::~FileLock() {
  30   Unlock();
  31 }
  32
  33 void FileLock::Lock() {
  34   if (acquired_)
  35     return;
  36   (*updating_)++;
  37   Barrier();
  38 }
  39
  40 void FileLock::Unlock() {
  41   if (!acquired_)
  42     return;
  43   Barrier();
  44   (*updating_)--;
  45 }
  46
  47 }  // namespace disk_cache