这通常是底层套接字的结果被关闭。 一把手，是因为文件中的底层C code使用的文件编号处理来识别手柄。该插座可以被你被关闭，但安全性异常，片状网络，它也可能被关闭等。

This is usually the result of the underlying socket being closed. The "number" is because file handles in the underlying C code use file numbers to identify handles. The socket may be closed by you, but it may also be closed by security exceptions, flaky network, etc.