！无论怎样都不应该在接收端关闭channel,因为在接收端无法判断发送端是否还会向通道中发送元素值

！试图向已经关闭的channel发送数据会导致panic

！关闭已经关闭的channel会导致panic

 

https://blog.csdn.net/qq_33296108/article/details/82731686