MultiContext: Contexts with sibling relationship

multicontext.go

// MultiContext allows you to use multiple contexts for cancellation
// allowing for sibling relationship, as well as parent-child relationship.
// This is an experiment, and likely not a good approach.
type MultiContext struct {
	ctxs []context.Context
	done chan struct{}
	err  error
}

func NewMultiContext(ctxs []context.Context) *MultiContext {
	done := make(chan struct{})
	mc := &MultiContext{ctxs, done, nil}
	for _, ctx := range ctxs {
		go func(ctx context.Context) {
			<-ctx.Done()
			mc.err = ctx.Err()
			close(done)
		}(ctx)
	}
	return mc
}

func (mc *MultiContext) Done() <-chan struct{} {
	return mc.done
}

func (mc *MultiContext) Err() error {
	return mc.err
}

func (mc *MultiContext) Deadline() (deadline time.Time, ok bool) {
	for _, ctx := range mc.ctxs {
		dl, ok := ctx.Deadline()
		if ok {
			return dl, ok
		}
	}
	return time.Time{}, false
}

func (mc *Multicontext) Value(key interface{}) interface{} {
	for _, ctx := range mc.ctxs {
		if val := ctx.Value(key); val != nil {
			return val
		}
	}
	return nil
}