Fix issue with manipulating the tree in Ascend

Co-authored-by: Stefan Bueringer <[email protected]>

pkg/controller/priorityqueue/priorityqueue.go

@@ -203,6 +203,9 @@ func (w *priorityqueue[T]) spin() {
 			w.lockedLock.Lock()
 			defer w.lockedLock.Unlock()
 
+			// manipulating the tree from within Ascend might lead to panics, so
+			// track what we want to delete and do it after we are done ascending.
+			var toDelete []*item[T]
 			w.queue.Ascend(func(item *item[T]) bool {
 				if item.readyAt != nil {
 					if readyAt := item.readyAt.Sub(w.now()); readyAt > 0 {
@@ -230,12 +233,16 @@ func (w *priorityqueue[T]) spin() {
 				w.locked.Insert(item.key)
 				w.waiters.Add(-1)
 				delete(w.items, item.key)
-				w.queue.Delete(item)
+				toDelete = append(toDelete, item)
 				w.becameReady.Delete(item.key)
 				w.get <- *item
 
 				return true
 			})
+
+			for _, item := range toDelete {
+				w.queue.Delete(item)
+			}
 		}()
 	}
 }

pkg/controller/priorityqueue/priorityqueue_test.go

@@ -2,6 +2,7 @@ package priorityqueue
 
 import (
 	"fmt"
+	"math/rand/v2"
 	"sync"
 	"testing"
 	"time"
@@ -344,6 +345,40 @@ var _ = Describe("Controllerworkqueue", func() {
 		Expect(metrics.depth["test"]).To(Equal(4))
 		metrics.mu.Unlock()
 	})
+
+	It("returns many items", func() {
+		// This test ensures the queue is able to drain a large queue without panic'ing.
+		// In a previous version of the code we were calling queue.Delete within q.Ascend
+		// which led to a panic in queue.Ascend > iterate:
+		// "panic: runtime error: index out of range [0] with length 0"
+		q, _ := newQueue()
+		defer q.ShutDown()
+
+		for range 20 {
+			for i := range 1000 {
+				rn := rand.N(100) //nolint:gosec // We don't need cryptographically secure entropy here
+				if rn < 10 {
+					q.AddWithOpts(AddOpts{After: time.Duration(rn) * time.Millisecond}, fmt.Sprintf("foo%d", i))
+				} else {
+					q.AddWithOpts(AddOpts{Priority: rn}, fmt.Sprintf("foo%d", i))
+				}
+			}
+
+			wg := sync.WaitGroup{}
+			for range 100 { // The panic only occurred relatively frequently with a high number of go routines.
+				wg.Add(1)
+				go func() {
+					defer wg.Done()
+					for range 10 {
+						obj, _, _ := q.GetWithPriority()
+						q.Done(obj)
+					}
+				}()
+			}
+
+			wg.Wait()
+		}
+	})
 })
 
 func BenchmarkAddGetDone(b *testing.B) {