runtime/runtime.go
func init() {
	http.HandleFunc("/_ah/background", handleBackground)

	sc := make(chan send)
	rc := make(chan recv)
	sendc, recvc = sc, rc
	go matchmaker(sc, rc)
}
func init() {
	http.HandleFunc("/_ah/background", handleBackground)

	sc := make(chan send)
	rc := make(chan recv)
	sendc, recvc = sc, rc
	go matchmaker(sc, rc)
}
/*
RunInBackground makes an API call that triggers an /_ah/background request.

There are two independent code paths that need to make contact:
the RunInBackground code, and the /_ah/background handler. The matchmaker
loop arranges for the two paths to meet. The RunInBackground code passes
a send to the matchmaker, the /_ah/background passes a recv to the matchmaker,
and the matchmaker hooks them up.
*/