private final ConcurrentMap<String, Object> locks = new ConcurrentHashMap<>();

    private List<ReferenceCountExchangeClient> getSharedClient(URL url, int connectNum) {
        String key = url.getAddress();
        // 略去无关代码

        // 【1】
        locks.putIfAbsent(key, new Object());

       // 【2】
        synchronized (locks.get(key)) {
            clients = referenceClientMap.get(key);
            if (checkClientCanUse(clients)) {
                batchClientRefIncr(clients);
                return clients;
            }
            connectNum = Math.max(connectNum, 1);
            if (CollectionUtils.isEmpty(clients)) {
                clients = buildReferenceCountExchangeClientList(url, connectNum);
                referenceClientMap.put(key, clients);
            } else {
                for (int i = 0; i < clients.size(); i++) {
                    ReferenceCountExchangeClient referenceCountExchangeClient = clients.get(i);
                    if (referenceCountExchangeClient == null || referenceCountExchangeClient.isClosed()) {
                        clients.set(i, buildReferenceCountExchangeClient(url));
                        continue;
                    }
                    referenceCountExchangeClient.incrementAndGetCount();
                }
            }

            // 【3】
            locks.remove(key);
            return clients;
        }
    }