Golang RWMutex.RLock方法代碼示例

func main() {
	var l *sync.RWMutex
	l = new(sync.RWMutex)
	l.RUnlock()
	fmt.Println("l")
	l.RLock()
}

func Task(f func(in Receiver, out Sender)) Sender {
	var running bool
	var l sync.RWMutex
	inR, inW := Pipe()
	outR, outW := Pipe()
	obj := NewServer()
	obj.OnAttach(Handler(func(msg *Message) error {
		msg.Ret.Send(&Message{Verb: Ack, Ret: inW})
		fmt.Printf("copying task output from %#v to %#v\n", outR, msg.Ret)
		defer fmt.Printf("(DONE) copying task output from %#v to %#v\n", outR, msg.Ret)
		Copy(msg.Ret, outR)
		return nil
	}))
	obj.OnStart(Handler(func(msg *Message) error {
		l.RLock()
		r := running
		l.RUnlock()
		if r {
			return fmt.Errorf("already running")
		}
		l.Lock()
		go f(inR, outW)
		running = true
		l.Unlock()
		msg.Ret.Send(&Message{Verb: Ack})
		return nil
	}))
	return obj
}

func TestSendReceiveWithWait(t *testing.T) {
	conn := NewConn()
	conn.ReceiveWait = true

	conn.Command("HGETALL", "person:1").ExpectMap(map[string]string{
		"name": "Mr. Johson",
		"age":  "42",
	})
	conn.Command("HGETALL", "person:2").ExpectMap(map[string]string{
		"name": "Ms. Jennifer",
		"age":  "28",
	})

	ids := []string{"1", "2"}
	for _, id := range ids {
		conn.Send("HGETALL", fmt.Sprintf("person:%s", id))
	}

	var people []Person
	var peopleLock sync.RWMutex

	go func() {
		for i := 0; i < len(ids); i++ {
			values, err := redis.Values(conn.Receive())
			if err != nil {
				t.Fatal(err)
			}

			var person Person
			err = redis.ScanStruct(values, &person)
			if err != nil {
				t.Fatal(err)
			}

			peopleLock.Lock()
			people = append(people, person)
			peopleLock.Unlock()
		}
	}()

	for i := 0; i < len(ids); i++ {
		conn.ReceiveNow <- true
	}
	time.Sleep(10 * time.Millisecond)

	peopleLock.RLock()
	defer peopleLock.RUnlock()

	if len(people) != 2 {
		t.Fatalf("Wrong number of people. Expected '2' and got '%d'", len(people))
	}

	if people[0].Name != "Mr. Johson" || people[1].Name != "Ms. Jennifer" {
		t.Error("People name order are wrong")
	}

	if people[0].Age != 42 || people[1].Age != 28 {
		t.Error("People age order are wrong")
	}
}

// Returns an Action that runs the original Action when there is no cached value.
// The cached value is unset after the given ttl (time to live) duration.
// A negative ttl will permanently cache
func (a Action) cache(ttl time.Duration) Action {
	var data map[string]interface{}
	lock := sync.RWMutex{}
	return func(r *http.Request) (map[string]interface{}, error) {
		lock.RLock()
		if data != nil {
			lock.RUnlock()
			return data, nil
		}
		lock.RUnlock()

		lock.Lock()
		defer lock.Unlock()
		var err error
		data, err = a(r)
		if data != nil {
			if ttl > 0 {
				time.AfterFunc(ttl, func() {
					lock.Lock()
					data = nil
					lock.Unlock()
				})
			}
		}
		return data, err
	}
}

// Readers-Writers
func rwlockExample() {
	runtime.GOMAXPROCS(runtime.NumCPU())
	// rand.Seed(time.Now().UnixNano())
	// rand.Seed(0)
	l := new(sync.RWMutex)
	wg := new(sync.WaitGroup)
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func(i int) {
			r := rand.Intn(10)
			time.Sleep(50 * time.Millisecond)
			if r < 5 {
				// I am reader.
				fmt.Printf("Reader waiting %d\n", i)
				l.RLock()
				fmt.Printf("go reader %d\n", i)
				l.RUnlock()
				wg.Done()
			} else {
				// I am writer
				fmt.Printf("Writer waiting %d\n", i)
				l.Lock()
				fmt.Printf("go writer %d\n", i)
				time.Sleep(50 * time.Millisecond)
				l.Unlock()
				wg.Done()
			}
		}(i)
	}
	wg.Wait()
}

func TestRaceRWMutexMultipleReaders(t *testing.T) {
	var mu sync.RWMutex
	var x, y int64 = 0, 1
	ch := make(chan bool, 3)
	go func() {
		mu.Lock()
		defer mu.Unlock()
		x = 2
		ch <- true
	}()
	go func() {
		mu.RLock()
		y = x + 1
		mu.RUnlock()
		ch <- true
	}()
	go func() {
		mu.RLock()
		y = x + 2
		mu.RUnlock()
		ch <- true
	}()
	<-ch
	<-ch
	<-ch
	_ = y
}

func TestStream_Open_WithOp(t *testing.T) {
	src := newStrSrc([]string{"HELLO", "WORLD", "HOW", "ARE", "YOU"})
	snk := newStrSink()
	op1 := api.UnFunc(func(ctx context.Context, data interface{}) interface{} {
		str := data.(string)
		return len(str)
	})

	var m sync.RWMutex
	runeCount := 0
	op2 := api.UnFunc(func(ctx context.Context, data interface{}) interface{} {
		length := data.(int)
		m.Lock()
		runeCount += length
		m.Unlock()
		return nil
	})

	strm := New().From(src).Transform(op1).Transform(op2).To(snk)
	select {
	case err := <-strm.Open():
		if err != nil {
			t.Fatal(err)
		}
	case <-time.After(50 * time.Millisecond):
		t.Fatal("Waited too long ...")
	}
	m.RLock()
	if runeCount != 19 {
		t.Fatal("Data not streaming, runeCount 19, got ", runeCount)
	}
	m.RUnlock()
}

// verifies the cacheWatcher.process goroutine is properly cleaned up even if
// the writes to cacheWatcher.result channel is blocked.
func TestCacheWatcherCleanupNotBlockedByResult(t *testing.T) {
	var lock sync.RWMutex
	count := 0
	filter := func(string, labels.Set, fields.Set) bool { return true }
	forget := func(bool) {
		lock.Lock()
		defer lock.Unlock()
		count++
	}
	initEvents := []watchCacheEvent{
		{Object: &api.Pod{}},
		{Object: &api.Pod{}},
	}
	// set the size of the buffer of w.result to 0, so that the writes to
	// w.result is blocked.
	w := newCacheWatcher(0, 0, initEvents, filter, forget)
	w.Stop()
	if err := wait.PollImmediate(1*time.Second, 5*time.Second, func() (bool, error) {
		lock.RLock()
		defer lock.RUnlock()
		return count == 2, nil
	}); err != nil {
		t.Fatalf("expected forget() to be called twice, because sendWatchCacheEvent should not be blocked by the result channel: %v", err)
	}
}

func TestNoRaceRWMutexMultipleReaders(t *testing.T) {
	var mu sync.RWMutex
	x := int64(0)
	ch := make(chan bool, 3)
	go func() {
		mu.Lock()
		defer mu.Unlock()
		x = 2
		ch <- true
	}()
	go func() {
		mu.RLock()
		y := x + 1
		_ = y
		mu.RUnlock()
		ch <- true
	}()
	go func() {
		mu.RLock()
		y := x + 2
		_ = y
		mu.RUnlock()
		ch <- true
	}()
	<-ch
	<-ch
	<-ch
}

func BenchmarkRWMutexR1(b *testing.B) {
	var mtx sync.RWMutex
	for i := 0; i < b.N; i++ {
		mtx.RLock()
		mtx.RUnlock()
	}
}

func BenchmarkRWMutexRLock(b *testing.B) {
	var l sync.RWMutex
	for i := 0; i < b.N; i++ {
		l.RLock()
		l.RUnlock()
	}
}

func compileVariableNode(node *parse.VariableNode, dotType reflect.Type, args []parse.Node, finalType reflect.Type) (cmd command, retType reflect.Type) {
	var mu sync.RWMutex
	type key struct {
		dotType, finalType reflect.Type
	}
	cache := make(map[key]command)

	name := node.Ident[0]
	cmd = func(s state, dot, final interface{}) interface{} {
		value := s.varValue(name)
		if len(node.Ident) == 1 {
			return value.Interface()
		}

		if dotType == nil {
			dotType = reflect.ValueOf(dot).Type()
		}
		if finalType == nil && final != nil {
			finalType = reflect.ValueOf(final).Type()
		}
		k := key{dotType, finalType}

		mu.RLock()
		f, exist := cache[k]
		mu.RUnlock()
		if !exist {
			f, _ = compileFieldChain(node.Ident[1:], dotType, args, finalType)
			mu.Lock()
			cache[k] = f
			mu.Unlock()
		}
		return f(s, dot, value)
	}
	return
}

func main() {
	Case := Init(6)
	fmt.Printf("DEADLOCK\n")

	c := make(chan int)
	var mu sync.RWMutex
	done := make(chan bool)
	go func() {
		time.Sleep(sleep3[Case][0])
		mu.RLock()
		c <- 1
		mu.RUnlock()
		done <- true
	}()
	go func() {
		time.Sleep(sleep3[Case][1])
		mu.RLock()
	loop:
		for {
			select {
			case <-c:
				break loop
			case <-time.After(time.Millisecond):
			}
		}
		mu.RUnlock()
		done <- true
	}()
	time.Sleep(sleep3[Case][2])
	mu.Lock()
	mu.Unlock()
	<-done
	<-done
}

func compileFieldDynamic(name string, args []parse.Node) lookupFn {
	type key struct {
		valueType reflect.Type
		finalType reflect.Type
	}

	var m sync.RWMutex
	cache := make(map[key]lookupFn)
	return func(s state, value reflect.Value, final interface{}) reflect.Value {
		valueType := value.Elem().Type()
		var finalType reflect.Type
		if v := reflect.ValueOf(final); v.IsValid() {
			finalType = v.Type()
		}

		k := key{valueType, finalType}
		m.RLock()
		f, exist := cache[k]
		m.RUnlock()
		if !exist {
			f, _ = compileField(valueType, name, args, finalType)
			m.Lock()
			cache[k] = f
			m.Unlock()
		}
		return f(s, value.Elem(), final)
	}
}

func main() {
	Case := Init(6)
	fmt.Printf("DEADLOCK\n")

	c := make(chan int)
	var mu sync.RWMutex
	done := make(chan bool)
	go func() {
		time.Sleep(sleep3[Case][0])
		mu.RLock()
		c <- 1
		mu.RUnlock()
		done <- true
	}()
	go func() {
		time.Sleep(sleep3[Case][1])
		mu.RLock()
		<-c
		mu.RUnlock()
		done <- true
	}()
	time.Sleep(sleep3[Case][2])
	mu.Lock()
	mu.Unlock()
	<-done
	<-done
}