readChan and unGetChan?

[Simon Marlow]

Li, Peng wrote:
> Suppose the following happens:
> 
> (1) Thread A calls readChan on an empty channel and waits
> (2) Thread B puts something to the read-end of the channel using unGetChan
> 
> When a GHC program does this, both threads are blocked! Is it the
> behaviour we really want for unGetChan, or should we fix the
> implementation for Control.Concurrent.Chan?

Good point.  Can you think of a good fix?

Interestingly, the STM TChan works perfectly in this respect.  Draw your 
own conclusion :)

Cheers,
	Simon