Just to be clear, goroutines aren't threads (although they are multiplexed onto threads), and they're only pre-empted at certain points in the go runtime (function calls are the big ones.)

If your request spins in a for-loop doing lots of work without function calls, other goroutines on the same thread won't get a chance to run, and you'll be limited to GOMAXPROCS simultaneous requests. In practice this never really happens though.