[Go - Note] Channel 阻塞deadlock和panic情况，以及close channel

阻塞：

发生一直阻塞时，会报如下deadlock错误：

fatal error: all goroutines are asleep - deadlock!

无缓存channel：

1. 通道中无数据，但执行读通道。
2. 通道中无数据，向通道写数据，但无协程读取。

有缓存channel：

1. 通道的缓存无数据，但执行读通道。
2. 通道的缓存已经占满，向通道写数据，但无协程读。

Panic：

1.向已经关闭的channel写。

2.关闭已经关闭的channel。

close channel：

You needn't close every channel when you've finished with it. It's only necessary to close a channel when it is important to tell the receiving goroutines that all data have been sent.

Note that it is only necessary to close a channel if the receiver is looking for a close. Closing the channel is a control signal on the channel indicating that no more data follows.

It's OK to leave a Go channel open forever and never close it. When the channel is no longer used, it will be garbage collected.