use map instead of list to cache blockage reasons

Author: maoqingyi

core/src/main/java/hudson/model/Queue.java

@@ -1616,7 +1616,7 @@ public void maintain() {
             updateSnapshot();
 
             // put label has no candidates here to accelerate the buildableItem circle
-            List<Label> noCandidateLabels = new ArrayList<>();
+            Map<Label, List<CauseOfBlockage>> noCandidateLabelsMap = new HashMap<>();
             // allocate buildable jobs to executors
             for (BuildableItem p : new ArrayList<>(
                     buildables)) { // copy as we'll mutate the list in the loop
@@ -1633,7 +1633,8 @@ public void maintain() {
                 }
 
                 Label itemLabel = p.getAssignedLabel();
-                if (noCandidateLabels.contains(itemLabel)) {
+                if (noCandidateLabelsMap.containsKey(itemLabel)) {
+                    p.transientCausesOfBlockage = noCandidateLabelsMap.get(itemLabel);
                     continue;
                 }
                 String taskDisplayName = LOGGER.isLoggable(Level.FINEST) ? p.task.getFullDisplayName() : null;
@@ -1679,9 +1680,9 @@ public void maintain() {
                                 new Object[]{p, candidates, parked.values()});
                         List<CauseOfBlockage> reasons = reasonMap.values().stream().filter(Objects::nonNull).collect(Collectors.toList());
                         p.transientCausesOfBlockage = reasons.isEmpty() ? null : reasons;
-                        // If no candidates, mark the label and end this loop early.
+                        // If no candidates, mark the label and reasons
                         if (candidates.isEmpty()) {
-                            noCandidateLabels.add(itemLabel);
+                            noCandidateLabelsMap.put(itemLabel, p.transientCausesOfBlockage);
                             LOGGER.log(Level.FINEST, "{0} changes to the state of no candidate executor", itemLabel);
                         }
                         continue;