おおまかにロジックを書いた

go.mod

@@ -0,0 +1,3 @@
+module github.com/sinmetalcraft/lane
+
+go 1.16

service.go

@@ -0,0 +1,59 @@
+package lane
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+)
+
+type Service struct {
+	lanes map[string]*Buzzer
+	mu    sync.Mutex
+}
+
+func NewService(ctx context.Context) (*Service, error) {
+	return &Service{
+		lanes: make(map[string]*Buzzer),
+	}, nil
+}
+
+type Buzzer struct {
+	GoSign chan bool
+	Expire time.Time
+	once   sync.Once
+}
+
+func (s *Service) LaneUp(ctx context.Context, key string, timeout time.Duration) (buzzer *Buzzer, goSign bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	buzzer, ok := s.lanes[key]
+	if !ok {
+		buzzer := &Buzzer{
+			GoSign: make(chan bool),
+			Expire: time.Now().Add(timeout),
+		}
+		s.lanes[key] = buzzer
+		return buzzer, true
+	}
+
+	return buzzer, false
+}
+
+func (s *Service) Done(ctx context.Context, key string) (err error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	buzzer, ok := s.lanes[key]
+	if !ok {
+		return fmt.Errorf("not found in the wait lane")
+	}
+
+	buzzer.once.Do(func() {
+		close(buzzer.GoSign)
+	})
+
+	delete(s.lanes, key)
+	return nil
+}

service_test.go

@@ -0,0 +1,64 @@
+package lane_test
+
+import (
+	"context"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/sinmetalcraft/lane"
+)
+
+func TestService_LaneUpAndDone(t *testing.T) {
+	ctx := context.Background()
+
+	s, err := lane.NewService(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	key := "hoge"
+	buzzer, goSign := s.LaneUp(ctx, key, 10*time.Second)
+	if buzzer == nil {
+		t.Error("buzzer is nil")
+	}
+	if e, g := true, goSign; e != g {
+		t.Errorf("want goSign %t but got %t", e, g)
+	}
+
+	receiveCounterCh := make(chan int)
+	wg := &sync.WaitGroup{}
+	const waitLineCount = 10
+	for i := 0; i < waitLineCount; i++ {
+		wg.Add(1)
+		go func(ctx context.Context, i int) {
+			buzzer, goSign := s.LaneUp(ctx, key, 10*time.Second)
+			if buzzer == nil {
+				t.Error("buzzer is nil")
+			}
+			if e, g := false, goSign; e != g {
+				t.Errorf("want goSign %t but got %t\n", e, g)
+			}
+			wg.Done() // 待ち行列に並んだことを通達
+
+			select {
+			case <-buzzer.GoSign:
+				receiveCounterCh <- i
+			case <-ctx.Done():
+				t.Error("context canceled")
+			}
+		}(ctx, i)
+	}
+
+	wg.Wait() // みんな待ち行列に並んで、待っている状態になった
+
+	// 処理が完了したら、待っているみんなに伝える
+	if err := s.Done(ctx, key); err != nil {
+		t.Fatal(err)
+	}
+
+	for i := 0; i < waitLineCount; i++ {
+		v := <-receiveCounterCh
+		t.Logf("done: %d\n", v)
+	}
+}