nodejs response.end（）在客户端挂起

Question

我尝试使用nodejs建立聊天并使用长轮询技术表达， 我为每个客户端保存名称和响应，以便在收到消息时结束它，下面是nodejs代码：

var q = parseQuery(req);
if (q.u){
    client = {};
    client.u = q.u;
    client.res = res;

    clients[q.u] = client;
    clientsLastMessagesMap[q.u] = 0;
}

但是当客户端收到消息时，我会尝试在服务器端和浏览器中发送保存在客户端对象中的响应，我发现它从未收到：

 for(var i in clients){
        var messages = "";
        while (clientsLastMessagesMap[clients[i].u] < messagesHistory.length){
            messages += messagesHistory[clientsLastMessagesMap[clients[i].u] ] + ",";
            clientsLastMessagesMap[clients[i].u]++;
        }
        if (messages !== ""){
            console.log( clients[i].u +  " should receive response ");
            clients[i].res.writeHead(200, {'Content-Type': 'text/plain'});
            clients[i].res.end();
        }
    }