boost的读写锁的使用

boost::shared_mutex _access;
void reader()
{
  // get shared access
  boost::shared_lock<boost::shared_mutex> lock(_access);
  // now we have shared access
}
void writer()
{
  // get upgradable access
  boost::upgrade_lock<boost::shared_mutex> lock(_access);
  // get exclusive access
  boost::upgrade_to_unique_lock<boost::shared_mutex> uniqueLock(lock);
  // now we have exclusive access
}