You're right that sync/atomic could've taken care of this, I wasn't aware of that package and figured channels were the way to go in Go.
As for making the waiting chan buffered, the reason I wanted to keep track of pending connections and active connections is because I'd like to proxy from a high-power server to a low-power server such as a Raspberry Pi. I agree with you that it could have done without though.
The demo doesn't seem to work on Chrome 25.0.1364.152 m. I'm getting this error whenever I try any of the shortcuts (or when I select a command from the drop down):
Uncaught TypeError: Cannot set property 'curOrigin' of undefined (infer.js:489)
For example you can put 10 in A1 and then put "=sum=0;for(i=0;i<A1;i++)sum+=i" in A2 to get the sum from 0 to 10. I really like this.