context/derive.go
func OnClosedContext(p goprocess.Process) context.Context {
	return &procContext{
		done:  p.Closed(),
		which: closed,
	}
}
func OnClosedContext(p goprocess.Process) context.Context {
	return &procContext{
		done:  p.Closed(),
		which: closed,
	}
}
// OnClosedContext derives a context from a given goprocess that will
// be 'Done' when the process is closed