timer: make sure timer which has a max delay will be scheduled first

pkg/timer/runtime/BUILD.bazel

@@ -35,7 +35,7 @@ go_test(
     embed = [":runtime"],
     flaky = True,
     race = "on",
-    shard_count = 23,
+    shard_count = 24,
     deps = [
         "//pkg/testkit/testsetup",
         "//pkg/timer/api",

pkg/timer/runtime/runtime.go

@@ -19,6 +19,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"maps"
+	"slices"
 	"sync"
 	"time"
 
@@ -252,9 +253,7 @@ func (rt *TimerGroupRuntime) fullRefreshTimers() {
 
 func (rt *TimerGroupRuntime) tryTriggerTimerEvents() {
 	now := rt.nowFunc()
-	var retryTimerIDs []string
-	var retryTimerKeys []string
-	var busyWorkers map[string]struct{}
+	var readyTimers []*timerCacheItem
 	rt.cache.iterTryTriggerTimers(func(timer *api.TimerRecord, tryTriggerTime time.Time, nextEventTime *time.Time) bool {
 		if tryTriggerTime.After(now) {
 			return false
@@ -264,9 +263,45 @@ func (rt *TimerGroupRuntime) tryTriggerTimerEvents() {
 			return true
 		}
 
+		if readyTimers == nil {
+			readyTimers = make([]*timerCacheItem, 0, 8)
+		}
+
+		readyTimers = append(readyTimers, &timerCacheItem{
+			timer:         timer,
+			nextEventTime: nextEventTime,
+		})
+		return true
+	})
+
+	if len(readyTimers) == 0 {
+		return
+	}
+
+	// resort timer to make sure the timer has the smallest nextEventTime has a higher priority to trigger
+	slices.SortFunc(readyTimers, func(a, b *timerCacheItem) int {
+		if a.nextEventTime == nil || b.nextEventTime == nil {
+			if a.nextEventTime != nil {
+				return 1
+			}
+
+			if b.nextEventTime != nil {
+				return -1
+			}
+
+			return 0
+		}
+		return a.nextEventTime.Compare(*b.nextEventTime)
+	})
+
+	var retryTimerIDs []string
+	var retryTimerKeys []string
+	var busyWorkers map[string]struct{}
+	for i, item := range readyTimers {
+		timer := item.timer
 		worker, ok := rt.ensureWorker(timer.HookClass)
 		if !ok {
-			return true
+			continue
 		}
 
 		eventID := timer.EventID
@@ -284,20 +319,22 @@ func (rt *TimerGroupRuntime) tryTriggerTimerEvents() {
 
 		select {
 		case <-rt.ctx.Done():
-			return false
+			return
 		case worker.ch <- req:
 			rt.cache.setTimerProcStatus(timer.ID, procTriggering, eventID)
 		default:
 			if busyWorkers == nil {
-				busyWorkers = make(map[string]struct{})
+				busySize := len(readyTimers) - i
+				retryTimerIDs = make([]string, 0, busySize)
+				retryTimerKeys = make([]string, 0, busySize)
+				busyWorkers = make(map[string]struct{}, busySize)
 			}
 
 			busyWorkers[timer.HookClass] = struct{}{}
 			retryTimerIDs = append(retryTimerIDs, timer.ID)
 			retryTimerKeys = append(retryTimerKeys, fmt.Sprintf("[%s] %s", timer.Namespace, timer.Key))
 		}
-		return true
-	})
+	}
 
 	if len(retryTimerIDs) > 0 {
 		busyWorkerList := make([]string, 0, len(busyWorkers))

pkg/timer/runtime/runtime_test.go

@@ -264,6 +264,51 @@ func TestTryTriggerTimer(t *testing.T) {
 	consumeAndVerify(t3)
 }
 
+func TestTryTriggerTimePriority(t *testing.T) {
+	now := time.Now()
+	store := api.NewMemoryTimerStore()
+	defer store.Close()
+	runtime := NewTimerRuntimeBuilder("g1", store).Build()
+	runtime.setNowFunc(func() time.Time {
+		return now
+	})
+	runtime.initCtx()
+	ch := make(chan *triggerEventRequest, 2)
+	runtime.workers["hook1"] = &hookWorker{ch: ch}
+
+	t1 := newTestTimer("t1", "1m", now.Add(-time.Hour))
+	runtime.cache.updateTimer(t1)
+	runtime.cache.updateNextTryTriggerTime(t1.ID, now.Add(-3*time.Minute))
+
+	t2 := newTestTimer("t2", "1m", now.Add(-2*time.Hour))
+	runtime.cache.updateTimer(t2)
+	runtime.cache.updateNextTryTriggerTime(t2.ID, now.Add(-2*time.Minute))
+
+	t3 := newTestTimer("t3", "1h", now)
+	t3.EventStatus = api.SchedEventTrigger
+	t3.EventID = "event2"
+	t3.EventStart = now.Add(-time.Minute)
+	t3.Enable = false
+	runtime.cache.updateTimer(t3)
+
+	t4 := newTestTimer("t4", "1m", now.Add(-10*time.Hour))
+	runtime.cache.updateTimer(t4)
+	runtime.cache.updateNextTryTriggerTime(t4.ID, now.Add(time.Minute))
+
+	// nextEventTime: t3 (nil) < t4 < t2 < t1
+	// nextTryTriggerTime: t1 < t2 < t3 (eventStart) < t4
+	// we should test the priority trigger is ordered by `nextEventTime` because to ensure the timer who has a max
+	// delay time will be triggered first.
+	// t4 should not be scheduled for the next trigger time is after now.
+	// so, t3 and t2 will be triggered when the capacity of chan is 2
+	runtime.tryTriggerTimerEvents()
+	require.Equal(t, procTriggering, runtime.cache.items[t2.ID].procStatus)
+	require.Equal(t, procTriggering, runtime.cache.items[t3.ID].procStatus)
+	// t1, t4 should keep not triggered
+	require.Equal(t, procIdle, runtime.cache.items[t1.ID].procStatus)
+	require.Equal(t, procIdle, runtime.cache.items[t4.ID].procStatus)
+}
+
 func TestHandleHookWorkerResponse(t *testing.T) {
 	now := time.Now()
 	store := api.NewMemoryTimerStore()