context/context_test.go - net - Git at Google

 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // +build !go1.7

 package context

 import (
 	"fmt"
 	"math/rand"
 	"runtime"
 	"strings"
 	"sync"
 	"testing"
 	"time"
 )

 // otherContext is a Context that's not one of the types defined in context.go.
 // This lets us test code paths that differ based on the underlying type of the
 // Context.
 type otherContext struct {
 	Context
 }

 func TestBackground(t *testing.T) {
 	c := Background()
 	if c == nil {
 		t.Fatalf("Background returned nil")
 	}
 	select {
 	case x := <-c.Done():
 		t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
 	default:
 	}
 	if got, want := fmt.Sprint(c), "context.Background"; got != want {
 		t.Errorf("Background().String() = %q want %q", got, want)
 	}
 }

 func TestTODO(t *testing.T) {
 	c := TODO()
 	if c == nil {
 		t.Fatalf("TODO returned nil")
 	}
 	select {
 	case x := <-c.Done():
 		t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
 	default:
 	}
 	if got, want := fmt.Sprint(c), "context.TODO"; got != want {
 		t.Errorf("TODO().String() = %q want %q", got, want)
 	}
 }

 func TestWithCancel(t *testing.T) {
 	c1, cancel := WithCancel(Background())

 	if got, want := fmt.Sprint(c1), "context.Background.WithCancel"; got != want {
 		t.Errorf("c1.String() = %q want %q", got, want)
 	}

 	o := otherContext{c1}
 	c2, _ := WithCancel(o)
 	contexts := []Context{c1, o, c2}

 	for i, c := range contexts {
 		if d := c.Done(); d == nil {
 			t.Errorf("c[%d].Done() == %v want non-nil", i, d)
 		}
 		if e := c.Err(); e != nil {
 			t.Errorf("c[%d].Err() == %v want nil", i, e)
 		}

 		select {
 		case x := <-c.Done():
 			t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
 		default:
 		}
 	}

 	cancel()
 	time.Sleep(100 * time.Millisecond) // let cancelation propagate

 	for i, c := range contexts {
 		select {
 		case <-c.Done():
 		default:
 			t.Errorf("<-c[%d].Done() blocked, but shouldn't have", i)
 		}
 		if e := c.Err(); e != Canceled {
 			t.Errorf("c[%d].Err() == %v want %v", i, e, Canceled)
 		}
 	}
 }

 func TestParentFinishesChild(t *testing.T) {
 	// Context tree:
 	// parent -> cancelChild
 	// parent -> valueChild -> timerChild
 	parent, cancel := WithCancel(Background())
 	cancelChild, stop := WithCancel(parent)
 	defer stop()
 	valueChild := WithValue(parent, "key", "value")
 	timerChild, stop := WithTimeout(valueChild, 10000*time.Hour)
 	defer stop()

 	select {
 	case x := <-parent.Done():
 		t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
 	case x := <-cancelChild.Done():
 		t.Errorf("<-cancelChild.Done() == %v want nothing (it should block)", x)
 	case x := <-timerChild.Done():
 		t.Errorf("<-timerChild.Done() == %v want nothing (it should block)", x)
 	case x := <-valueChild.Done():
 		t.Errorf("<-valueChild.Done() == %v want nothing (it should block)", x)
 	default:
 	}

 	// The parent's children should contain the two cancelable children.
 	pc := parent.(*cancelCtx)
 	cc := cancelChild.(*cancelCtx)
 	tc := timerChild.(*timerCtx)
 	pc.mu.Lock()
 	if len(pc.children) != 2 || !pc.children[cc] || !pc.children[tc] {
 		t.Errorf("bad linkage: pc.children = %v, want %v and %v",
 			pc.children, cc, tc)
 	}
 	pc.mu.Unlock()

 	if p, ok := parentCancelCtx(cc.Context); !ok || p != pc {
 		t.Errorf("bad linkage: parentCancelCtx(cancelChild.Context) = %v, %v want %v, true", p, ok, pc)
 	}
 	if p, ok := parentCancelCtx(tc.Context); !ok || p != pc {
 		t.Errorf("bad linkage: parentCancelCtx(timerChild.Context) = %v, %v want %v, true", p, ok, pc)
 	}

 	cancel()

 	pc.mu.Lock()
 	if len(pc.children) != 0 {
 		t.Errorf("pc.cancel didn't clear pc.children = %v", pc.children)
 	}
 	pc.mu.Unlock()

 	// parent and children should all be finished.
 	check := func(ctx Context, name string) {
 		select {
 		case <-ctx.Done():
 		default:
 			t.Errorf("<-%s.Done() blocked, but shouldn't have", name)
 		}
 		if e := ctx.Err(); e != Canceled {
 			t.Errorf("%s.Err() == %v want %v", name, e, Canceled)
 		}
 	}
 	check(parent, "parent")
 	check(cancelChild, "cancelChild")
 	check(valueChild, "valueChild")
 	check(timerChild, "timerChild")

 	// WithCancel should return a canceled context on a canceled parent.
 	precanceledChild := WithValue(parent, "key", "value")
 	select {
 	case <-precanceledChild.Done():
 	default:
 		t.Errorf("<-precanceledChild.Done() blocked, but shouldn't have")
 	}
 	if e := precanceledChild.Err(); e != Canceled {
 		t.Errorf("precanceledChild.Err() == %v want %v", e, Canceled)
 	}
 }

 func TestChildFinishesFirst(t *testing.T) {
 	cancelable, stop := WithCancel(Background())
 	defer stop()
 	for _, parent := range []Context{Background(), cancelable} {
 		child, cancel := WithCancel(parent)

 		select {
 		case x := <-parent.Done():
 			t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
 		case x := <-child.Done():
 			t.Errorf("<-child.Done() == %v want nothing (it should block)", x)
 		default:
 		}

 		cc := child.(*cancelCtx)
 		pc, pcok := parent.(*cancelCtx) // pcok == false when parent == Background()
 		if p, ok := parentCancelCtx(cc.Context); ok != pcok || (ok && pc != p) {
 			t.Errorf("bad linkage: parentCancelCtx(cc.Context) = %v, %v want %v, %v", p, ok, pc, pcok)
 		}

 		if pcok {
 			pc.mu.Lock()
 			if len(pc.children) != 1 || !pc.children[cc] {
 				t.Errorf("bad linkage: pc.children = %v, cc = %v", pc.children, cc)
 			}
 			pc.mu.Unlock()
 		}

 		cancel()

 		if pcok {
 			pc.mu.Lock()
 			if len(pc.children) != 0 {
 				t.Errorf("child's cancel didn't remove self from pc.children = %v", pc.children)
 			}
 			pc.mu.Unlock()
 		}

 		// child should be finished.
 		select {
 		case <-child.Done():
 		default:
 			t.Errorf("<-child.Done() blocked, but shouldn't have")
 		}
 		if e := child.Err(); e != Canceled {
 			t.Errorf("child.Err() == %v want %v", e, Canceled)
 		}

 		// parent should not be finished.
 		select {
 		case x := <-parent.Done():
 			t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
 		default:
 		}
 		if e := parent.Err(); e != nil {
 			t.Errorf("parent.Err() == %v want nil", e)
 		}
 	}
 }

 func testDeadline(c Context, wait time.Duration, t *testing.T) {
 	select {
 	case <-time.After(wait):
 		t.Fatalf("context should have timed out")
 	case <-c.Done():
 	}
 	if e := c.Err(); e != DeadlineExceeded {
 		t.Errorf("c.Err() == %v want %v", e, DeadlineExceeded)
 	}
 }

 func TestDeadline(t *testing.T) {
 	t.Parallel()
 	const timeUnit = 500 * time.Millisecond
 	c, _ := WithDeadline(Background(), time.Now().Add(1*timeUnit))
 	if got, prefix := fmt.Sprint(c), "context.Background.WithDeadline("; !strings.HasPrefix(got, prefix) {
 		t.Errorf("c.String() = %q want prefix %q", got, prefix)
 	}
 	testDeadline(c, 2*timeUnit, t)

 	c, _ = WithDeadline(Background(), time.Now().Add(1*timeUnit))
 	o := otherContext{c}
 	testDeadline(o, 2*timeUnit, t)

 	c, _ = WithDeadline(Background(), time.Now().Add(1*timeUnit))
 	o = otherContext{c}
 	c, _ = WithDeadline(o, time.Now().Add(3*timeUnit))
 	testDeadline(c, 2*timeUnit, t)
 }

 func TestTimeout(t *testing.T) {
 	t.Parallel()
 	const timeUnit = 500 * time.Millisecond
 	c, _ := WithTimeout(Background(), 1*timeUnit)
 	if got, prefix := fmt.Sprint(c), "context.Background.WithDeadline("; !strings.HasPrefix(got, prefix) {
 		t.Errorf("c.String() = %q want prefix %q", got, prefix)
 	}
 	testDeadline(c, 2*timeUnit, t)

 	c, _ = WithTimeout(Background(), 1*timeUnit)
 	o := otherContext{c}
 	testDeadline(o, 2*timeUnit, t)

 	c, _ = WithTimeout(Background(), 1*timeUnit)
 	o = otherContext{c}
 	c, _ = WithTimeout(o, 3*timeUnit)
 	testDeadline(c, 2*timeUnit, t)
 }

 func TestCanceledTimeout(t *testing.T) {
 	t.Parallel()
 	const timeUnit = 500 * time.Millisecond
 	c, _ := WithTimeout(Background(), 2*timeUnit)
 	o := otherContext{c}
 	c, cancel := WithTimeout(o, 4*timeUnit)
 	cancel()
 	time.Sleep(1 * timeUnit) // let cancelation propagate
 	select {
 	case <-c.Done():
 	default:
 		t.Errorf("<-c.Done() blocked, but shouldn't have")
 	}
 	if e := c.Err(); e != Canceled {
 		t.Errorf("c.Err() == %v want %v", e, Canceled)
 	}
 }

 type key1 int
 type key2 int

 var k1 = key1(1)
 var k2 = key2(1) // same int as k1, different type
 var k3 = key2(3) // same type as k2, different int

 func TestValues(t *testing.T) {
 	check := func(c Context, nm, v1, v2, v3 string) {
 		if v, ok := c.Value(k1).(string); ok == (len(v1) == 0) || v != v1 {
 			t.Errorf(`%s.Value(k1).(string) = %q, %t want %q, %t`, nm, v, ok, v1, len(v1) != 0)
 		}
 		if v, ok := c.Value(k2).(string); ok == (len(v2) == 0) || v != v2 {
 			t.Errorf(`%s.Value(k2).(string) = %q, %t want %q, %t`, nm, v, ok, v2, len(v2) != 0)
 		}
 		if v, ok := c.Value(k3).(string); ok == (len(v3) == 0) || v != v3 {
 			t.Errorf(`%s.Value(k3).(string) = %q, %t want %q, %t`, nm, v, ok, v3, len(v3) != 0)
 		}
 	}

 	c0 := Background()
 	check(c0, "c0", "", "", "")

 	c1 := WithValue(Background(), k1, "c1k1")
 	check(c1, "c1", "c1k1", "", "")

 	if got, want := fmt.Sprint(c1), `context.Background.WithValue(1, "c1k1")`; got != want {
 		t.Errorf("c.String() = %q want %q", got, want)
 	}

 	c2 := WithValue(c1, k2, "c2k2")
 	check(c2, "c2", "c1k1", "c2k2", "")

 	c3 := WithValue(c2, k3, "c3k3")
 	check(c3, "c2", "c1k1", "c2k2", "c3k3")

 	c4 := WithValue(c3, k1, nil)
 	check(c4, "c4", "", "c2k2", "c3k3")

 	o0 := otherContext{Background()}
 	check(o0, "o0", "", "", "")

 	o1 := otherContext{WithValue(Background(), k1, "c1k1")}
 	check(o1, "o1", "c1k1", "", "")

 	o2 := WithValue(o1, k2, "o2k2")
 	check(o2, "o2", "c1k1", "o2k2", "")

 	o3 := otherContext{c4}
 	check(o3, "o3", "", "c2k2", "c3k3")

 	o4 := WithValue(o3, k3, nil)
 	check(o4, "o4", "", "c2k2", "")
 }

 func TestAllocs(t *testing.T) {
 	bg := Background()
 	for _, test := range []struct {
 		desc       string
 		f          func()
 		limit      float64
 		gccgoLimit float64
 	}{
 		{
 			desc:       "Background()",
 			f:          func() { Background() },
 			limit:      0,
 			gccgoLimit: 0,
 		},
 		{
 			desc: fmt.Sprintf("WithValue(bg, %v, nil)", k1),
 			f: func() {
 				c := WithValue(bg, k1, nil)
 				c.Value(k1)
 			},
 			limit:      3,
 			gccgoLimit: 3,
 		},
 		{
 			desc: "WithTimeout(bg, 15*time.Millisecond)",
 			f: func() {
 				c, _ := WithTimeout(bg, 15*time.Millisecond)
 				<-c.Done()
 			},
 			limit:      8,
 			gccgoLimit: 16,
 		},
 		{
 			desc: "WithCancel(bg)",
 			f: func() {
 				c, cancel := WithCancel(bg)
 				cancel()
 				<-c.Done()
 			},
 			limit:      5,
 			gccgoLimit: 8,
 		},
 		{
 			desc: "WithTimeout(bg, 100*time.Millisecond)",
 			f: func() {
 				c, cancel := WithTimeout(bg, 100*time.Millisecond)
 				cancel()
 				<-c.Done()
 			},
 			limit:      8,
 			gccgoLimit: 25,
 		},
 	} {
 		limit := test.limit
 		if runtime.Compiler == "gccgo" {
 			// gccgo does not yet do escape analysis.
 			// TODO(iant): Remove this when gccgo does do escape analysis.
 			limit = test.gccgoLimit
 		}
 		if n := testing.AllocsPerRun(100, test.f); n > limit {
 			t.Errorf("%s allocs = %f want %d", test.desc, n, int(limit))
 		}
 	}
 }

 func TestSimultaneousCancels(t *testing.T) {
 	root, cancel := WithCancel(Background())
 	m := map[Context]CancelFunc{root: cancel}
 	q := []Context{root}
 	// Create a tree of contexts.
 	for len(q) != 0 && len(m) < 100 {
 		parent := q[0]
 		q = q[1:]
 		for i := 0; i < 4; i++ {
 			ctx, cancel := WithCancel(parent)
 			m[ctx] = cancel
 			q = append(q, ctx)
 		}
 	}
 	// Start all the cancels in a random order.
 	var wg sync.WaitGroup
 	wg.Add(len(m))
 	for _, cancel := range m {
 		go func(cancel CancelFunc) {
 			cancel()
 			wg.Done()
 		}(cancel)
 	}
 	// Wait on all the contexts in a random order.
 	for ctx := range m {
 		select {
 		case <-ctx.Done():
 		case <-time.After(1 * time.Second):
 			buf := make([]byte, 10<<10)
 			n := runtime.Stack(buf, true)
 			t.Fatalf("timed out waiting for <-ctx.Done(); stacks:\n%s", buf[:n])
 		}
 	}
 	// Wait for all the cancel functions to return.
 	done := make(chan struct{})
 	go func() {
 		wg.Wait()
 		close(done)
 	}()
 	select {
 	case <-done:
 	case <-time.After(1 * time.Second):
 		buf := make([]byte, 10<<10)
 		n := runtime.Stack(buf, true)
 		t.Fatalf("timed out waiting for cancel functions; stacks:\n%s", buf[:n])
 	}
 }

 func TestInterlockedCancels(t *testing.T) {
 	parent, cancelParent := WithCancel(Background())
 	child, cancelChild := WithCancel(parent)
 	go func() {
 		parent.Done()
 		cancelChild()
 	}()
 	cancelParent()
 	select {
 	case <-child.Done():
 	case <-time.After(1 * time.Second):
 		buf := make([]byte, 10<<10)
 		n := runtime.Stack(buf, true)
 		t.Fatalf("timed out waiting for child.Done(); stacks:\n%s", buf[:n])
 	}
 }

 func TestLayersCancel(t *testing.T) {
 	testLayers(t, time.Now().UnixNano(), false)
 }

 func TestLayersTimeout(t *testing.T) {
 	testLayers(t, time.Now().UnixNano(), true)
 }

 func testLayers(t *testing.T, seed int64, testTimeout bool) {
 	rand.Seed(seed)
 	errorf := func(format string, a ...interface{}) {
 		t.Errorf(fmt.Sprintf("seed=%d: %s", seed, format), a...)
 	}
 	const (
 		timeout   = 200 * time.Millisecond
 		minLayers = 30
 	)
 	type value int
 	var (
 		vals      []*value
 		cancels   []CancelFunc
 		numTimers int
 		ctx       = Background()
 	)
 	for i := 0; i < minLayers || numTimers == 0 || len(cancels) == 0 || len(vals) == 0; i++ {
 		switch rand.Intn(3) {
 		case 0:
 			v := new(value)
 			ctx = WithValue(ctx, v, v)
 			vals = append(vals, v)
 		case 1:
 			var cancel CancelFunc
 			ctx, cancel = WithCancel(ctx)
 			cancels = append(cancels, cancel)
 		case 2:
 			var cancel CancelFunc
 			ctx, cancel = WithTimeout(ctx, timeout)
 			cancels = append(cancels, cancel)
 			numTimers++
 		}
 	}
 	checkValues := func(when string) {
 		for _, key := range vals {
 			if val := ctx.Value(key).(*value); key != val {
 				errorf("%s: ctx.Value(%p) = %p want %p", when, key, val, key)
 			}
 		}
 	}
 	select {
 	case <-ctx.Done():
 		errorf("ctx should not be canceled yet")
 	default:
 	}
 	if s, prefix := fmt.Sprint(ctx), "context.Background."; !strings.HasPrefix(s, prefix) {
 		t.Errorf("ctx.String() = %q want prefix %q", s, prefix)
 	}
 	t.Log(ctx)
 	checkValues("before cancel")
 	if testTimeout {
 		select {
 		case <-ctx.Done():
 		case <-time.After(timeout + 100*time.Millisecond):
 			errorf("ctx should have timed out")
 		}
 		checkValues("after timeout")
 	} else {
 		cancel := cancels[rand.Intn(len(cancels))]
 		cancel()
 		select {
 		case <-ctx.Done():
 		default:
 			errorf("ctx should be canceled")
 		}
 		checkValues("after cancel")
 	}
 }

 func TestCancelRemoves(t *testing.T) {
 	checkChildren := func(when string, ctx Context, want int) {
 		if got := len(ctx.(*cancelCtx).children); got != want {
 			t.Errorf("%s: context has %d children, want %d", when, got, want)
 		}
 	}

 	ctx, _ := WithCancel(Background())
 	checkChildren("after creation", ctx, 0)
 	_, cancel := WithCancel(ctx)
 	checkChildren("with WithCancel child ", ctx, 1)
 	cancel()
 	checkChildren("after cancelling WithCancel child", ctx, 0)

 	ctx, _ = WithCancel(Background())
 	checkChildren("after creation", ctx, 0)
 	_, cancel = WithTimeout(ctx, 60*time.Minute)
 	checkChildren("with WithTimeout child ", ctx, 1)
 	cancel()
 	checkChildren("after cancelling WithTimeout child", ctx, 0)
 }
	// Copyright 2014 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// +build !go1.7

	package context

	import (
	"fmt"
	"math/rand"
	"runtime"
	"strings"
	"sync"
	"testing"
	"time"
	)

	// otherContext is a Context that's not one of the types defined in context.go.
	// This lets us test code paths that differ based on the underlying type of the
	// Context.
	type otherContext struct {
	Context
	}

	func TestBackground(t *testing.T) {
	c := Background()
	if c == nil {
	t.Fatalf("Background returned nil")
	}
	select {
	case x := <-c.Done():
	t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
	default:
	}
	if got, want := fmt.Sprint(c), "context.Background"; got != want {
	t.Errorf("Background().String() = %q want %q", got, want)
	}
	}

	func TestTODO(t *testing.T) {
	c := TODO()
	if c == nil {
	t.Fatalf("TODO returned nil")
	}
	select {
	case x := <-c.Done():
	t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
	default:
	}
	if got, want := fmt.Sprint(c), "context.TODO"; got != want {
	t.Errorf("TODO().String() = %q want %q", got, want)
	}
	}

	func TestWithCancel(t *testing.T) {
	c1, cancel := WithCancel(Background())

	if got, want := fmt.Sprint(c1), "context.Background.WithCancel"; got != want {
	t.Errorf("c1.String() = %q want %q", got, want)
	}

	o := otherContext{c1}
	c2, _ := WithCancel(o)
	contexts := []Context{c1, o, c2}

	for i, c := range contexts {
	if d := c.Done(); d == nil {
	t.Errorf("c[%d].Done() == %v want non-nil", i, d)
	}
	if e := c.Err(); e != nil {
	t.Errorf("c[%d].Err() == %v want nil", i, e)
	}

	select {
	case x := <-c.Done():
	t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
	default:
	}
	}

	cancel()
	time.Sleep(100 * time.Millisecond) // let cancelation propagate

	for i, c := range contexts {
	select {
	case <-c.Done():
	default:
	t.Errorf("<-c[%d].Done() blocked, but shouldn't have", i)
	}
	if e := c.Err(); e != Canceled {
	t.Errorf("c[%d].Err() == %v want %v", i, e, Canceled)
	}
	}
	}

	func TestParentFinishesChild(t *testing.T) {
	// Context tree:
	// parent -> cancelChild
	// parent -> valueChild -> timerChild
	parent, cancel := WithCancel(Background())
	cancelChild, stop := WithCancel(parent)
	defer stop()
	valueChild := WithValue(parent, "key", "value")
	timerChild, stop := WithTimeout(valueChild, 10000*time.Hour)
	defer stop()

	select {
	case x := <-parent.Done():
	t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
	case x := <-cancelChild.Done():
	t.Errorf("<-cancelChild.Done() == %v want nothing (it should block)", x)
	case x := <-timerChild.Done():
	t.Errorf("<-timerChild.Done() == %v want nothing (it should block)", x)
	case x := <-valueChild.Done():
	t.Errorf("<-valueChild.Done() == %v want nothing (it should block)", x)
	default:
	}

	// The parent's children should contain the two cancelable children.
	pc := parent.(*cancelCtx)
	cc := cancelChild.(*cancelCtx)
	tc := timerChild.(*timerCtx)
	pc.mu.Lock()
	if len(pc.children) != 2 \|\| !pc.children[cc] \|\| !pc.children[tc] {
	t.Errorf("bad linkage: pc.children = %v, want %v and %v",
	pc.children, cc, tc)
	}
	pc.mu.Unlock()

	if p, ok := parentCancelCtx(cc.Context); !ok \|\| p != pc {
	t.Errorf("bad linkage: parentCancelCtx(cancelChild.Context) = %v, %v want %v, true", p, ok, pc)
	}
	if p, ok := parentCancelCtx(tc.Context); !ok \|\| p != pc {
	t.Errorf("bad linkage: parentCancelCtx(timerChild.Context) = %v, %v want %v, true", p, ok, pc)
	}

	cancel()

	pc.mu.Lock()
	if len(pc.children) != 0 {
	t.Errorf("pc.cancel didn't clear pc.children = %v", pc.children)
	}
	pc.mu.Unlock()

	// parent and children should all be finished.
	check := func(ctx Context, name string) {
	select {
	case <-ctx.Done():
	default:
	t.Errorf("<-%s.Done() blocked, but shouldn't have", name)
	}
	if e := ctx.Err(); e != Canceled {
	t.Errorf("%s.Err() == %v want %v", name, e, Canceled)
	}
	}
	check(parent, "parent")
	check(cancelChild, "cancelChild")
	check(valueChild, "valueChild")
	check(timerChild, "timerChild")

	// WithCancel should return a canceled context on a canceled parent.
	precanceledChild := WithValue(parent, "key", "value")
	select {
	case <-precanceledChild.Done():
	default:
	t.Errorf("<-precanceledChild.Done() blocked, but shouldn't have")
	}
	if e := precanceledChild.Err(); e != Canceled {
	t.Errorf("precanceledChild.Err() == %v want %v", e, Canceled)
	}
	}

	func TestChildFinishesFirst(t *testing.T) {
	cancelable, stop := WithCancel(Background())
	defer stop()
	for _, parent := range []Context{Background(), cancelable} {
	child, cancel := WithCancel(parent)

	select {
	case x := <-parent.Done():
	t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
	case x := <-child.Done():
	t.Errorf("<-child.Done() == %v want nothing (it should block)", x)
	default:
	}

	cc := child.(*cancelCtx)
	pc, pcok := parent.(*cancelCtx) // pcok == false when parent == Background()
	if p, ok := parentCancelCtx(cc.Context); ok != pcok \|\| (ok && pc != p) {
	t.Errorf("bad linkage: parentCancelCtx(cc.Context) = %v, %v want %v, %v", p, ok, pc, pcok)
	}

	if pcok {
	pc.mu.Lock()
	if len(pc.children) != 1 \|\| !pc.children[cc] {
	t.Errorf("bad linkage: pc.children = %v, cc = %v", pc.children, cc)
	}
	pc.mu.Unlock()
	}

	cancel()

	if pcok {
	pc.mu.Lock()
	if len(pc.children) != 0 {
	t.Errorf("child's cancel didn't remove self from pc.children = %v", pc.children)
	}
	pc.mu.Unlock()
	}

	// child should be finished.
	select {
	case <-child.Done():
	default:
	t.Errorf("<-child.Done() blocked, but shouldn't have")
	}
	if e := child.Err(); e != Canceled {
	t.Errorf("child.Err() == %v want %v", e, Canceled)
	}

	// parent should not be finished.
	select {
	case x := <-parent.Done():
	t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
	default:
	}
	if e := parent.Err(); e != nil {
	t.Errorf("parent.Err() == %v want nil", e)
	}
	}
	}

	func testDeadline(c Context, wait time.Duration, t *testing.T) {
	select {
	case <-time.After(wait):
	t.Fatalf("context should have timed out")
	case <-c.Done():
	}
	if e := c.Err(); e != DeadlineExceeded {
	t.Errorf("c.Err() == %v want %v", e, DeadlineExceeded)
	}
	}

	func TestDeadline(t *testing.T) {
	t.Parallel()
	const timeUnit = 500 * time.Millisecond
	c, _ := WithDeadline(Background(), time.Now().Add(1*timeUnit))
	if got, prefix := fmt.Sprint(c), "context.Background.WithDeadline("; !strings.HasPrefix(got, prefix) {
	t.Errorf("c.String() = %q want prefix %q", got, prefix)
	}
	testDeadline(c, 2*timeUnit, t)

	c, _ = WithDeadline(Background(), time.Now().Add(1*timeUnit))
	o := otherContext{c}
	testDeadline(o, 2*timeUnit, t)

	c, _ = WithDeadline(Background(), time.Now().Add(1*timeUnit))
	o = otherContext{c}
	c, _ = WithDeadline(o, time.Now().Add(3*timeUnit))
	testDeadline(c, 2*timeUnit, t)
	}

	func TestTimeout(t *testing.T) {
	t.Parallel()
	const timeUnit = 500 * time.Millisecond
	c, _ := WithTimeout(Background(), 1*timeUnit)
	if got, prefix := fmt.Sprint(c), "context.Background.WithDeadline("; !strings.HasPrefix(got, prefix) {
	t.Errorf("c.String() = %q want prefix %q", got, prefix)
	}
	testDeadline(c, 2*timeUnit, t)

	c, _ = WithTimeout(Background(), 1*timeUnit)
	o := otherContext{c}
	testDeadline(o, 2*timeUnit, t)

	c, _ = WithTimeout(Background(), 1*timeUnit)
	o = otherContext{c}
	c, _ = WithTimeout(o, 3*timeUnit)
	testDeadline(c, 2*timeUnit, t)
	}

	func TestCanceledTimeout(t *testing.T) {
	t.Parallel()
	const timeUnit = 500 * time.Millisecond
	c, _ := WithTimeout(Background(), 2*timeUnit)
	o := otherContext{c}
	c, cancel := WithTimeout(o, 4*timeUnit)
	cancel()
	time.Sleep(1 * timeUnit) // let cancelation propagate
	select {
	case <-c.Done():
	default:
	t.Errorf("<-c.Done() blocked, but shouldn't have")
	}
	if e := c.Err(); e != Canceled {
	t.Errorf("c.Err() == %v want %v", e, Canceled)
	}
	}

	type key1 int
	type key2 int

	var k1 = key1(1)
	var k2 = key2(1) // same int as k1, different type
	var k3 = key2(3) // same type as k2, different int

	func TestValues(t *testing.T) {
	check := func(c Context, nm, v1, v2, v3 string) {
	if v, ok := c.Value(k1).(string); ok == (len(v1) == 0) \|\| v != v1 {
	t.Errorf(`%s.Value(k1).(string) = %q, %t want %q, %t`, nm, v, ok, v1, len(v1) != 0)
	}
	if v, ok := c.Value(k2).(string); ok == (len(v2) == 0) \|\| v != v2 {
	t.Errorf(`%s.Value(k2).(string) = %q, %t want %q, %t`, nm, v, ok, v2, len(v2) != 0)
	}
	if v, ok := c.Value(k3).(string); ok == (len(v3) == 0) \|\| v != v3 {
	t.Errorf(`%s.Value(k3).(string) = %q, %t want %q, %t`, nm, v, ok, v3, len(v3) != 0)
	}
	}

	c0 := Background()
	check(c0, "c0", "", "", "")

	c1 := WithValue(Background(), k1, "c1k1")
	check(c1, "c1", "c1k1", "", "")

	if got, want := fmt.Sprint(c1), `context.Background.WithValue(1, "c1k1")`; got != want {
	t.Errorf("c.String() = %q want %q", got, want)
	}

	c2 := WithValue(c1, k2, "c2k2")
	check(c2, "c2", "c1k1", "c2k2", "")

	c3 := WithValue(c2, k3, "c3k3")
	check(c3, "c2", "c1k1", "c2k2", "c3k3")

	c4 := WithValue(c3, k1, nil)
	check(c4, "c4", "", "c2k2", "c3k3")

	o0 := otherContext{Background()}
	check(o0, "o0", "", "", "")

	o1 := otherContext{WithValue(Background(), k1, "c1k1")}
	check(o1, "o1", "c1k1", "", "")

	o2 := WithValue(o1, k2, "o2k2")
	check(o2, "o2", "c1k1", "o2k2", "")

	o3 := otherContext{c4}
	check(o3, "o3", "", "c2k2", "c3k3")

	o4 := WithValue(o3, k3, nil)
	check(o4, "o4", "", "c2k2", "")
	}

	func TestAllocs(t *testing.T) {
	bg := Background()
	for _, test := range []struct {
	desc string
	f func()
	limit float64
	gccgoLimit float64
	}{
	{
	desc: "Background()",
	f: func() { Background() },
	limit: 0,
	gccgoLimit: 0,
	},
	{
	desc: fmt.Sprintf("WithValue(bg, %v, nil)", k1),
	f: func() {
	c := WithValue(bg, k1, nil)
	c.Value(k1)
	},
	limit: 3,
	gccgoLimit: 3,
	},
	{
	desc: "WithTimeout(bg, 15*time.Millisecond)",
	f: func() {
	c, _ := WithTimeout(bg, 15*time.Millisecond)
	<-c.Done()
	},
	limit: 8,
	gccgoLimit: 16,
	},
	{
	desc: "WithCancel(bg)",
	f: func() {
	c, cancel := WithCancel(bg)
	cancel()
	<-c.Done()
	},
	limit: 5,
	gccgoLimit: 8,
	},
	{
	desc: "WithTimeout(bg, 100*time.Millisecond)",
	f: func() {
	c, cancel := WithTimeout(bg, 100*time.Millisecond)
	cancel()
	<-c.Done()
	},
	limit: 8,
	gccgoLimit: 25,
	},
	} {
	limit := test.limit
	if runtime.Compiler == "gccgo" {
	// gccgo does not yet do escape analysis.
	// TODO(iant): Remove this when gccgo does do escape analysis.
	limit = test.gccgoLimit
	}
	if n := testing.AllocsPerRun(100, test.f); n > limit {
	t.Errorf("%s allocs = %f want %d", test.desc, n, int(limit))
	}
	}
	}

	func TestSimultaneousCancels(t *testing.T) {
	root, cancel := WithCancel(Background())
	m := map[Context]CancelFunc{root: cancel}
	q := []Context{root}
	// Create a tree of contexts.
	for len(q) != 0 && len(m) < 100 {
	parent := q[0]
	q = q[1:]
	for i := 0; i < 4; i++ {
	ctx, cancel := WithCancel(parent)
	m[ctx] = cancel
	q = append(q, ctx)
	}
	}
	// Start all the cancels in a random order.
	var wg sync.WaitGroup
	wg.Add(len(m))
	for _, cancel := range m {
	go func(cancel CancelFunc) {
	cancel()
	wg.Done()
	}(cancel)
	}
	// Wait on all the contexts in a random order.
	for ctx := range m {
	select {
	case <-ctx.Done():
	case <-time.After(1 * time.Second):
	buf := make([]byte, 10<<10)
	n := runtime.Stack(buf, true)
	t.Fatalf("timed out waiting for <-ctx.Done(); stacks:\n%s", buf[:n])
	}
	}
	// Wait for all the cancel functions to return.
	done := make(chan struct{})
	go func() {
	wg.Wait()
	close(done)
	}()
	select {
	case <-done:
	case <-time.After(1 * time.Second):
	buf := make([]byte, 10<<10)
	n := runtime.Stack(buf, true)
	t.Fatalf("timed out waiting for cancel functions; stacks:\n%s", buf[:n])
	}
	}

	func TestInterlockedCancels(t *testing.T) {
	parent, cancelParent := WithCancel(Background())
	child, cancelChild := WithCancel(parent)
	go func() {
	parent.Done()
	cancelChild()
	}()
	cancelParent()
	select {
	case <-child.Done():
	case <-time.After(1 * time.Second):
	buf := make([]byte, 10<<10)
	n := runtime.Stack(buf, true)
	t.Fatalf("timed out waiting for child.Done(); stacks:\n%s", buf[:n])
	}
	}

	func TestLayersCancel(t *testing.T) {
	testLayers(t, time.Now().UnixNano(), false)
	}

	func TestLayersTimeout(t *testing.T) {
	testLayers(t, time.Now().UnixNano(), true)
	}

	func testLayers(t *testing.T, seed int64, testTimeout bool) {
	rand.Seed(seed)
	errorf := func(format string, a ...interface{}) {
	t.Errorf(fmt.Sprintf("seed=%d: %s", seed, format), a...)
	}
	const (
	timeout = 200 * time.Millisecond
	minLayers = 30
	)
	type value int
	var (
	vals []*value
	cancels []CancelFunc
	numTimers int
	ctx = Background()
	)
	for i := 0; i < minLayers \|\| numTimers == 0 \|\| len(cancels) == 0 \|\| len(vals) == 0; i++ {
	switch rand.Intn(3) {
	case 0:
	v := new(value)
	ctx = WithValue(ctx, v, v)
	vals = append(vals, v)
	case 1:
	var cancel CancelFunc
	ctx, cancel = WithCancel(ctx)
	cancels = append(cancels, cancel)
	case 2:
	var cancel CancelFunc
	ctx, cancel = WithTimeout(ctx, timeout)
	cancels = append(cancels, cancel)
	numTimers++
	}
	}
	checkValues := func(when string) {
	for _, key := range vals {
	if val := ctx.Value(key).(*value); key != val {
	errorf("%s: ctx.Value(%p) = %p want %p", when, key, val, key)
	}
	}
	}
	select {
	case <-ctx.Done():
	errorf("ctx should not be canceled yet")
	default:
	}
	if s, prefix := fmt.Sprint(ctx), "context.Background."; !strings.HasPrefix(s, prefix) {
	t.Errorf("ctx.String() = %q want prefix %q", s, prefix)
	}
	t.Log(ctx)
	checkValues("before cancel")
	if testTimeout {
	select {
	case <-ctx.Done():
	case <-time.After(timeout + 100*time.Millisecond):
	errorf("ctx should have timed out")
	}
	checkValues("after timeout")
	} else {
	cancel := cancels[rand.Intn(len(cancels))]
	cancel()
	select {
	case <-ctx.Done():
	default:
	errorf("ctx should be canceled")
	}
	checkValues("after cancel")
	}
	}

	func TestCancelRemoves(t *testing.T) {
	checkChildren := func(when string, ctx Context, want int) {
	if got := len(ctx.(*cancelCtx).children); got != want {
	t.Errorf("%s: context has %d children, want %d", when, got, want)
	}
	}

	ctx, _ := WithCancel(Background())
	checkChildren("after creation", ctx, 0)
	_, cancel := WithCancel(ctx)
	checkChildren("with WithCancel child ", ctx, 1)
	cancel()
	checkChildren("after cancelling WithCancel child", ctx, 0)

	ctx, _ = WithCancel(Background())
	checkChildren("after creation", ctx, 0)
	_, cancel = WithTimeout(ctx, 60*time.Minute)
	checkChildren("with WithTimeout child ", ctx, 1)
	cancel()
	checkChildren("after cancelling WithTimeout child", ctx, 0)
	}