Alerting: Ticker to support stopping (#48142)

* add stop for ticker
* stop ticker when scheduler stops
* stop ticker when legacy engine stops

pkg/services/alerting/engine.go

@@ -97,6 +97,7 @@ func ProvideAlertEngine(renderer rendering.Service, requestValidator models.Plug
 func (e *AlertEngine) Run(ctx context.Context) error {
 	reg := prometheus.WrapRegistererWithPrefix("legacy_", prometheus.DefaultRegisterer)
 	e.ticker = NewTicker(clock.New(), 1*time.Second, metrics.NewTickerMetrics(reg))
+	defer e.ticker.Stop()
 	alertGroup, ctx := errgroup.WithContext(ctx)
 	alertGroup.Go(func() error { return e.alertingTicker(ctx) })
 	alertGroup.Go(func() error { return e.runJobDispatcher(ctx) })

pkg/services/alerting/ticker.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/benbjohnson/clock"
 
+	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/services/alerting/metrics"
 )
 
@@ -20,6 +21,7 @@ type Ticker struct {
 	last     time.Time
 	interval time.Duration
 	metrics  *metrics.Ticker
+	stopCh   chan struct{}
 }
 
 // NewTicker returns a Ticker that ticks on interval marks (or very shortly after) starting at c.Now(), and never drops ticks. interval should not be negative or zero.
@@ -33,6 +35,7 @@ func NewTicker(c clock.Clock, interval time.Duration, metric *metrics.Ticker) *T
 		last:     c.Now(),
 		interval: interval,
 		metrics:  metric,
+		stopCh:   make(chan struct{}),
 	}
 	metric.IntervalSeconds.Set(t.interval.Seconds()) // Seconds report fractional part as well, so it matches the format of the timestamp we report below
 	go t.run()
@@ -40,18 +43,39 @@ func NewTicker(c clock.Clock, interval time.Duration, metric *metrics.Ticker) *T
 }
 
 func (t *Ticker) run() {
+	logger := log.New("ticker")
+	logger.Info("starting")
+LOOP:
 	for {
 		next := t.last.Add(t.interval) // calculate the time of the next tick
 		t.metrics.NextTickTime.Set(float64(next.UnixNano()) / 1e9)
 		diff := t.clock.Now().Sub(next) // calculate the difference between the current time and the next tick
 		// if difference is not negative, then it should tick
 		if diff >= 0 {
-			t.C <- next
+			select {
+			case t.C <- next:
+			case <-t.stopCh:
+				break LOOP
+			}
 			t.last = next
 			t.metrics.LastTickTime.Set(float64(next.UnixNano()) / 1e9)
 			continue
 		}
 		// tick is too young. try again when ...
-		<-t.clock.After(-diff) // ...it'll definitely be old enough
+		select {
+		case <-t.clock.After(-diff): // ...it'll definitely be old enough
+		case <-t.stopCh:
+			break LOOP
+		}
+	}
+	logger.Info("stopped", "last_tick", t.last)
+}
+
+// Stop stops the ticker. It does not close the C channel
+func (t *Ticker) Stop() {
+	select {
+	case t.stopCh <- struct{}{}:
+	default:
+		// already stopped
 	}
 }

pkg/services/alerting/ticker_test.go

@@ -18,7 +18,12 @@ import (
 )
 
 func TestTicker(t *testing.T) {
-	readChanOrFail := func(t *testing.T, ctx context.Context, c chan time.Time) time.Time {
+	readChanOrFail := func(t *testing.T, c chan time.Time) time.Time {
+		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+		t.Cleanup(func() {
+			cancel()
+		})
+
 		t.Helper()
 		select {
 		case tick := <-c:
@@ -76,11 +81,8 @@ func TestTicker(t *testing.T) {
 				break
 			}
 		}
-		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-		t.Cleanup(func() {
-			cancel()
-		})
-		actual := readChanOrFail(t, ctx, ticker.C)
+
+		actual := readChanOrFail(t, ticker.C)
 		require.Equal(t, expectedTick, actual)
 	})
 
@@ -97,18 +99,13 @@ func TestTicker(t *testing.T) {
 		clk.Add(interval) // advance the clock by the interval to make the ticker tick the first time.
 		clk.Add(interval) // advance the clock by the interval to make the ticker tick the second time.
 
-		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-		t.Cleanup(func() {
-			cancel()
-		})
-
 		// Irregardless of wall time, the first tick should be initial clock + interval.
-		actual1 := readChanOrFail(t, ctx, ticker.C)
+		actual1 := readChanOrFail(t, ticker.C)
 		require.Equal(t, expectedTick, actual1)
 
 		var actual2 time.Time
 		require.Eventually(t, func() bool {
-			actual2 = readChanOrFail(t, ctx, ticker.C)
+			actual2 = readChanOrFail(t, ticker.C)
 			return true
 		}, time.Second, 10*time.Millisecond)
 
@@ -147,11 +144,7 @@ func TestTicker(t *testing.T) {
 		}, 1*time.Second, 100*time.Millisecond, "failed to wait for metrics to match expected values:\n%v", errs)
 
 		clk.Add(interval)
-		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-		t.Cleanup(func() {
-			cancel()
-		})
-		actual := readChanOrFail(t, ctx, ticker.C)
+		actual := readChanOrFail(t, ticker.C)
 
 		expectedMetric = fmt.Sprintf(expectedMetricFmt, interval.Seconds(), float64(actual.UnixNano())/1e9, float64(expectedTick.Add(interval).UnixNano())/1e9)
 
@@ -163,4 +156,35 @@ func TestTicker(t *testing.T) {
 			return err == nil
 		}, 1*time.Second, 100*time.Millisecond, "failed to wait for metrics to match expected values:\n%v", errs)
 	})
+
+	t.Run("should stop", func(t *testing.T) {
+		t.Run("when it waits for the next tick", func(t *testing.T) {
+			clk := clock.NewMock()
+			interval := time.Duration(rand.Int63n(9)+1) * time.Second
+			ticker := NewTicker(clk, interval, metrics.NewTickerMetrics(prometheus.NewRegistry()))
+			clk.Add(interval)
+			readChanOrFail(t, ticker.C)
+			ticker.Stop()
+			clk.Add(interval)
+			require.Empty(t, ticker.C)
+		})
+
+		t.Run("when it waits for the tick to be consumed", func(t *testing.T) {
+			clk := clock.NewMock()
+			interval := time.Duration(rand.Int63n(9)+1) * time.Second
+			ticker := NewTicker(clk, interval, metrics.NewTickerMetrics(prometheus.NewRegistry()))
+			clk.Add(interval)
+			ticker.Stop()
+			require.Empty(t, ticker.C)
+		})
+
+		t.Run("multiple times", func(t *testing.T) {
+			clk := clock.NewMock()
+			interval := time.Duration(rand.Int63n(9)+1) * time.Second
+			ticker := NewTicker(clk, interval, metrics.NewTickerMetrics(prometheus.NewRegistry()))
+			ticker.Stop()
+			ticker.Stop()
+			ticker.Stop()
+		})
+	})
 }

pkg/services/ngalert/CHANGELOG.md

@@ -59,6 +59,7 @@ Scopes must have an order to ensure consistency and ease of search, this helps u
 - [BUGFIX] RBAC: replace create\update\delete actions for notification policies by alert.notifications:write #49185
 - [BUGFIX] Fix access to alerts for Viewer role with editor permissions in folder #49270
 - [FEATURE] Alert rules with associated panels will take screenshots. #49293 #49338 #49374 #49377 #49378 #49379 #49381 #49385 #49439 #49445
+- [ENHANCEMENT] Scheduler: ticker to support stopping #48142
 
 ## 8.5.3
 
@@ -81,4 +82,3 @@ Scopes must have an order to ensure consistency and ease of search, this helps u
 - [BUGFIX] (Legacy) Templates: Parse notification templates using all the matches of the alert rule when going from `Alerting` to `OK` in legacy alerting #47355
 - [BUGFIX] Scheduler: Fix state manager to support OK option of `AlertRule.ExecErrState` #47670
 - [ENHANCEMENT] Templates: Enable the use of classic condition values in templates #46971
-

pkg/services/ngalert/schedule/schedule.go

@@ -156,6 +156,8 @@ func (sch *schedule) Run(ctx context.Context) error {
 	var wg sync.WaitGroup
 	wg.Add(2)
 
+	defer sch.ticker.Stop()
+
 	go func() {
 		defer wg.Done()
 		if err := sch.schedulePeriodic(ctx); err != nil {
@@ -652,6 +654,7 @@ func (sch *schedule) saveAlertStates(ctx context.Context, states []*state.State)
 func (sch *schedule) overrideCfg(cfg SchedulerCfg) {
 	sch.clock = cfg.C
 	sch.baseInterval = cfg.BaseInterval
+	sch.ticker.Stop()
 	sch.ticker = alerting.NewTicker(cfg.C, cfg.BaseInterval, cfg.Metrics.Ticker)
 	sch.evalAppliedFunc = cfg.EvalAppliedFunc
 	sch.stopAppliedFunc = cfg.StopAppliedFunc