Use current resourceUsage value as historyUsage when leader change in…

… ThresholdShedder (#13136)

### Motivation
Fix #13119

### Modification
1. User current resourceUsage value as historyUsage value when leader change in ThresholdShedder to speed up getting the actual historyUsage value.

(cherry picked from commit 6d9d24d)

pulsar-broker/src/main/java/org/apache/pulsar/broker/loadbalance/impl/ThresholdShedder.java

@@ -38,13 +38,9 @@
 
 public class ThresholdShedder implements LoadSheddingStrategy {
     private static final Logger log = LoggerFactory.getLogger(ThresholdShedder.class);
-
     private final Multimap<String, String> selectedBundlesCache = ArrayListMultimap.create();
-
     private static final double ADDITIONAL_THRESHOLD_PERCENT_MARGIN = 0.05;
-
     private static final double MB = 1024 * 1024;
-
     private final Map<String, Double> brokerAvgResourceUsage = new HashMap<>();
 
     @Override
@@ -139,25 +135,27 @@ private double getBrokerAvgUsage(final LoadData loadData, final double historyPe
         for (Map.Entry<String, BrokerData> entry : loadData.getBrokerData().entrySet()) {
             LocalBrokerData localBrokerData = entry.getValue().getLocalData();
             String broker = entry.getKey();
-            updateAvgResourceUsage(broker, localBrokerData, historyPercentage, conf);
-            totalUsage += brokerAvgResourceUsage.getOrDefault(broker, 0.0);
+            totalUsage += updateAvgResourceUsage(broker, localBrokerData, historyPercentage, conf);
             totalBrokers++;
         }
 
         return totalBrokers > 0 ? totalUsage / totalBrokers : 0;
     }
 
-    private void updateAvgResourceUsage(String broker, LocalBrokerData localBrokerData, final double historyPercentage,
-                                        final ServiceConfiguration conf) {
-        double historyUsage =
-                brokerAvgResourceUsage.getOrDefault(broker, 0.0);
-        historyUsage = historyUsage * historyPercentage
-                + (1 - historyPercentage) * localBrokerData.getMaxResourceUsageWithWeight(
+    private double updateAvgResourceUsage(String broker, LocalBrokerData localBrokerData,
+                                          final double historyPercentage, final ServiceConfiguration conf) {
+        Double historyUsage =
+                brokerAvgResourceUsage.get(broker);
+        double resourceUsage = localBrokerData.getMaxResourceUsageWithWeight(
                 conf.getLoadBalancerCPUResourceWeight(),
                 conf.getLoadBalancerMemoryResourceWeight(), conf.getLoadBalancerDirectMemoryResourceWeight(),
                 conf.getLoadBalancerBandwithInResourceWeight(),
                 conf.getLoadBalancerBandwithOutResourceWeight());
+        historyUsage = historyUsage == null
+                ? resourceUsage : historyUsage * historyPercentage + (1 - historyPercentage) * resourceUsage;
+
         brokerAvgResourceUsage.put(broker, historyUsage);
+        return historyUsage;
     }
 
 }