/**
* Delays completing of given future until the returned action is called.
**/
public static Tpl <Future <A>, Action> delayUntilSignal <A>(this Future <A> future)
{
Promise <Unit> signalP;
var f = future.zip(Future <Unit> .async(out signalP), (a, _) => a);
Action act = () => signalP.tryComplete(F.unit);
return(F.t(f, act));
}
