util: fractional context

util/ctx/fracctx.go

+package ctxutil
+
+import (
+	"time"
+
+	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
+)
+
+func WithDeadlineFraction(ctx context.Context, fraction float64) (context.Context, context.CancelFunc) {
+	d, found := ctx.Deadline()
+	if !found { // no deadline
+		return context.WithCancel(ctx)
+	}
+
+	left := d.Sub(time.Now())
+	if left < 0 { // already passed...
+		return context.WithCancel(ctx)
+	}
+
+	left = time.Duration(float64(left) * fraction)
+	return context.WithTimeout(ctx, left)
+}

util/ctx/fracctx_test.go

+package ctxutil
+
+import (
+	"testing"
+	"time"
+
+	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
+)
+
+// this test is on the context tool itself, not our stuff. it's for sanity on ours.
+func TestDeadline(t *testing.T) {
+	ctx, _ := context.WithTimeout(context.Background(), 5*time.Millisecond)
+
+	select {
+	case <-ctx.Done():
+		t.Fatal("ended too early")
+	default:
+	}
+
+	<-time.After(6 * time.Millisecond)
+
+	select {
+	case <-ctx.Done():
+	default:
+		t.Fatal("ended too late")
+	}
+}
+
+func TestDeadlineFractionForever(t *testing.T) {
+
+	ctx, _ := WithDeadlineFraction(context.Background(), 0.5)
+
+	_, found := ctx.Deadline()
+	if found {
+		t.Fatal("should last forever")
+	}
+}
+
+func TestDeadlineFractionHalf(t *testing.T) {
+
+	ctx1, _ := context.WithTimeout(context.Background(), 10*time.Millisecond)
+	ctx2, _ := WithDeadlineFraction(ctx1, 0.5)
+
+	select {
+	case <-ctx1.Done():
+		t.Fatal("ctx1 ended too early")
+	case <-ctx2.Done():
+		t.Fatal("ctx2 ended too early")
+	default:
+	}
+
+	<-time.After(2 * time.Millisecond)
+
+	select {
+	case <-ctx1.Done():
+		t.Fatal("ctx1 ended too early")
+	case <-ctx2.Done():
+		t.Fatal("ctx2 ended too early")
+	default:
+	}
+
+	<-time.After(4 * time.Millisecond)
+
+	select {
+	case <-ctx1.Done():
+		t.Fatal("ctx1 ended too early")
+	case <-ctx2.Done():
+	default:
+		t.Fatal("ctx2 ended too late")
+	}
+
+	<-time.After(6 * time.Millisecond)
+
+	select {
+	case <-ctx1.Done():
+	default:
+		t.Fatal("ctx1 ended too late")
+	}
+
+}
+
+func TestDeadlineFractionCancel(t *testing.T) {
+
+	ctx1, cancel1 := context.WithTimeout(context.Background(), 10*time.Millisecond)
+	ctx2, cancel2 := WithDeadlineFraction(ctx1, 0.5)
+
+	select {
+	case <-ctx1.Done():
+		t.Fatal("ctx1 ended too early")
+	case <-ctx2.Done():
+		t.Fatal("ctx2 ended too early")
+	default:
+	}
+
+	cancel2()
+
+	select {
+	case <-ctx1.Done():
+		t.Fatal("ctx1 should NOT be cancelled")
+	case <-ctx2.Done():
+	default:
+		t.Fatal("ctx2 should be cancelled")
+	}
+
+	cancel1()
+
+	select {
+	case <-ctx1.Done():
+	case <-ctx2.Done():
+	default:
+		t.Fatal("ctx1 should be cancelled")
+	}
+
+}
+
+func TestDeadlineFractionObeysParent(t *testing.T) {
+
+	ctx1, cancel1 := context.WithTimeout(context.Background(), 10*time.Millisecond)
+	ctx2, _ := WithDeadlineFraction(ctx1, 0.5)
+
+	select {
+	case <-ctx1.Done():
+		t.Fatal("ctx1 ended too early")
+	case <-ctx2.Done():
+		t.Fatal("ctx2 ended too early")
+	default:
+	}
+
+	cancel1()
+
+	select {
+	case <-ctx2.Done():
+	default:
+		t.Fatal("ctx2 should be cancelled")
+	}
+
+}