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

阻塞：

發生一直阻塞時，會報以下deadlock錯誤：

fatal error: all goroutines are asleep - deadlock!

無緩存channel：

1. 通道中無數據，但執行讀通道。
2. 通道中無數據，向通道寫數據，但無協程讀取。

有緩存channel：

1. 通道的緩存無數據，但執行讀通道。
2. 通道的緩存已經佔滿，向通道寫數據，但無協程讀。

Panic：

1.向已經關閉的channel寫。
2.關閉已經關閉的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.