fix: race in PriorityQueue.Pop by checking emptiness under write lock (#15726)

* fix: race in PriorityQueue.Pop by checking emptiness under write lock

* Create sashass1315_fix-priority-queue-pop-lock-race

* Update changelog/sashass1315_fix-priority-queue-pop-lock-race

Co-authored-by: Preston Van Loon <preston@prysmaticlabs.com>

* Move changelog/sashass1315_fix-priority-queue-pop-lock-race to changelog/sashass1315_fix-priority-queue-pop-lock-race.md

* Fix bullet in changelog

---------

Co-authored-by: Preston Van Loon <preston@prysmaticlabs.com>
Co-authored-by: Preston Van Loon <pvanloon@offchainlabs.com>

changelog/sashass1315_fix-priority-queue-pop-lock-race.md

@@ -0,0 +1,2 @@
+### Fixed
+- fix race in PriorityQueue.Pop by checking emptiness under write lock. (#15726)

container/queue/priority_queue.go

@@ -86,13 +86,13 @@ func (pq *PriorityQueue) Len() int {
 // wrapper/convenience method that calls heap.Pop, so consumers do not need to
 // invoke heap functions directly
 func (pq *PriorityQueue) Pop() (*Item, error) {
-	if pq.Len() == 0 {
-		return nil, ErrEmpty
-	}
-
 	pq.lock.Lock()
 	defer pq.lock.Unlock()
 
+	if pq.data.Len() == 0 {
+		return nil, ErrEmpty
+	}
+
 	item, ok := heap.Pop(&pq.data).(*Item)
 	if !ok {
 		return nil, errors.New("unknown type")