void ResourceDispatcherHostImpl::Shutdown() {
  DCHECK_CURRENTLY_ON(BrowserThread::UI);
  BrowserThread::PostTask(BrowserThread::IO,
                          FROM_HERE,
                          base::Bind(&ResourceDispatcherHostImpl::OnShutdown,
                                     base::Unretained(this)));
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.