Channel closing behavior in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens when you close a channel in Go?

Closing a channel means no more values can be sent on it. Receivers can still receive remaining values until the channel is empty, then they get the zero value.

beginner

Can you send values on a closed channel?

No. Sending on a closed channel causes a runtime panic (error).

intermediate

What does a receive operation return when the channel is closed and empty?

It returns the zero value of the channel's type and false for the second value if using the two-value receive form.

intermediate

How can you check if a channel is closed when receiving?

Use the two-value receive: v, ok := <-ch. If ok is false, the channel is closed and empty.

intermediate

Is it safe to close a channel from multiple goroutines?

No. Closing a channel multiple times causes a panic. Only one goroutine should close the channel.

What happens if you try to send a value on a closed channel?

A The program panics (runtime error).

B The value is silently ignored.

C The value is buffered until the channel reopens.

D The send blocks forever.

Sending on a closed channel causes a runtime panic in Go.

When receiving from a closed channel, what value do you get?

A The receive blocks forever.

B The last sent value again.

C An error is returned.

D The zero value of the channel's type.

After a channel is closed and emptied, receives return the zero value of the channel's type.

How do you detect if a channel is closed when receiving?

A Use a select statement with default case.

B Use the two-value receive: v, ok := <-ch.

C Check if the channel is nil.

D You cannot detect if a channel is closed.

The two-value receive form returns ok=false when the channel is closed and empty.

Who should close a channel?

A Any goroutine at any time.

B The receiver, when done receiving.

C The sender, when no more values will be sent.

D Channels do not need to be closed.

The sender should close the channel to signal no more values will be sent.

What happens if multiple goroutines close the same channel?

A The program panics at the second close.

B The channel closes safely once.

C The channel reopens automatically.

D The closes are ignored after the first.

Closing a channel more than once causes a panic.

Explain what happens when a Go channel is closed and how receivers behave afterwards.

Think about what sending and receiving do after closing.

Describe best practices for closing channels in concurrent Go programs.

Who should close and why?