Reproduce race in go/vt/throttle

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

go/vt/throttler/throttler_test.go

@@ -17,11 +17,16 @@ limitations under the License.
 package throttler
 
 import (
+	"context"
 	"runtime"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/require"
+
+	"vitess.io/vitess/go/vt/discovery"
+	"vitess.io/vitess/go/vt/proto/query"
+	"vitess.io/vitess/go/vt/proto/topodata"
 )
 
 // The main purpose of the benchmarks below is to demonstrate the functionality
@@ -398,3 +403,52 @@ func TestThreadFinished_SecondCallPanics(t *testing.T) {
 	}()
 	throttler.ThreadFinished(0)
 }
+
+func TestThrottlerMaxLag(t *testing.T) {
+	fc := &fakeClock{}
+	throttler, _ := newThrottlerWithClock("test", "queries", 1, 1, ReplicationLagModuleDisabled, fc.now)
+	defer throttler.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	go func(ctx context.Context, throttler *Throttler) {
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			default:
+				for _, tabletType := range []topodata.TabletType{
+					topodata.TabletType_REPLICA,
+					topodata.TabletType_RDONLY,
+				} {
+					throttler.MaxLag(tabletType)
+				}
+			}
+		}
+	}(ctx, throttler)
+
+	go func(cancel context.CancelFunc, throttler *Throttler) {
+		defer cancel()
+		for _, tabletType := range []topodata.TabletType{
+			topodata.TabletType_REPLICA,
+			topodata.TabletType_RDONLY,
+		} {
+			cache := throttler.maxReplicationLagModule.lagCacheByType(tabletType)
+			cache.add(replicationLagRecord{
+				time: time.Now(),
+				TabletHealth: discovery.TabletHealth{
+					Serving: true,
+					Stats: &query.RealtimeStats{
+						ReplicationLagSeconds: 5,
+					},
+					Tablet: &topodata.Tablet{
+						Hostname: t.Name(),
+						PortMap: map[string]int32{
+							"test": 15999,
+						},
+					},
+				},
+			})
+		}
+	}(cancel, throttler)
+}