Synchronized on `String#intern` is a bad practice, interning a string will make it a global object .Which means if you synchronized the same interned strings in different parts of your code , some shit'll happen ,eg : deadlock

https://github.com/alibaba/dubbo/blob/9cf27a36848c22fbfd00877449fbe0eaf53e040c/dubbo-rpc/dubbo-rpc-default/src/main/java/com/alibaba/dubbo/rpc/protocol/dubbo/DubboProtocol.java#L333
ReferenceCountExchangeClient client = referenceClientMap.get(key);
        if (client != null) {
            if (!client.isClosed()) {
                client.incrementAndGetCount();
                return client;
            } else {
                referenceClientMap.remove(key);
            }
        }
        synchronized (key.intern()) {
            ExchangeClient exchangeClient = initClient(url);
            client = new ReferenceCountExchangeClient(exchangeClient, ghostClientMap);
            referenceClientMap.put(key, client);
            ghostClientMap.remove(key);
            return client;
        }
    }
    /**
     * Create new connection
     */
    private ExchangeClient initClient(URL url) {
        
        String str = url.getParameter(Constants.CLIENT_KEY, url.getParameter(Constants.SERVER_KEY, Constants.DEFAULT_REMOTING_CLIENT));
        url = url.addParameter(Constants.CODEC_KEY, DubboCodec.NAME);
        
        url = url.addParameterIfAbsent(Constants.HEARTBEAT_KEY, String.valueOf(Constants.DEFAULT_HEARTBEAT));
        
        if (str != null && str.length() > 0 && !ExtensionLoader.getExtensionLoader(Transporter.class).hasExtension(str)) {
            throw new RpcException("Unsupported client type: " + str + "," +
                    " supported client type is " + StringUtils.join(ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions(), " "));