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