使用tcp调试工具，三个客户端同时去给服务端发心跳，导致执行一半就执行下一条了

echo "===\n";
echo 1."\n";
echo 2."\n";

echo "===\n";
echo 3."\n";
echo 4."\n";

===
1
2
===
3
4

===
1
===
3
2
4