Fix private DNS not working due to getConnectCounter() stuck am: 3c07ec67 am: 31e07936

DnsTlsTransport::Response DnsTlsDispatcher::query(const DnsTlsServer& server, unsigned mark,

                                                  const Slice query, const Slice ans, int* resplen,

                                                  bool* connectTriggered) {

    int connectCounter;

    // TODO: This can cause the resolver to create multiple connections to the same DoT server

    // merely due to different mark, such as the bit explicitlySelected unset.

    // See if we can save them and just create one connection for one DoT server.

            xport = it->second.get();

        }

        ++xport->useCount;

        connectCounter = xport->transport.getConnectCounter();

    }

    // Don't call this function and hold sLock at the same time because of the following reason:

    // TLS handshake requires a lock which is also needed by this function, if the handshake gets

    // stuck, this function also gets blocked.

    const int connectCounter = xport->transport.getConnectCounter();

    LOG(DEBUG) << "Sending query of length " << query.size();

    auto res = xport->transport.query(query);

    LOG(DEBUG) << "Awaiting response";

    const auto& result = res.get();

    *connectTriggered = (xport->transport.getConnectCounter() > connectCounter);

    DnsTlsTransport::Response code = result.code;

    if (code == DnsTlsTransport::Response::success) {

        if (result.response.size() > ans.size()) {

    auto now = std::chrono::steady_clock::now();

    {

        std::lock_guard guard(sLock);

        *connectTriggered = (xport->transport.getConnectCounter() > connectCounter);

        --xport->useCount;

        xport->lastUsed = now;

        cleanup(now);