Make stream closing atomic

[henry118]

Fixes: #8930

closeWithError() is not atomic, which may result in a race situation where the recv channel is closed right before we write to the channel, but after checking recvErr is nil.

[dmcgowan]

Another option could be instead of creating a mutex, never close recv and instead have a recvClose channel. Whenever a select is used on recv, check for the recvClose channel instead of checking if recv is closed. I know it looks a little uglier, but it is less likely to deadlock. Using a lock here has the risk of getting in a recv/close deadlock (consumer of recv channel is trying to close).

[henry118]

Got it. I'll close this PR then.