Fix the issue of high CPU load caused by continuously creating new ConsistentHashSelector instances under high concurrency (#15497)

Author: DustinQiao

dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/loadbalance/ConsistentHashLoadBalance.java

@@ -53,13 +53,13 @@ public class ConsistentHashLoadBalance extends AbstractLoadBalance {
     protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {
         String methodName = RpcUtils.getMethodName(invocation);
         String key = invokers.get(0).getUrl().getServiceKey() + "." + methodName;
-        // using the hashcode of list to compute the hash only pay attention to the elements in the list
         int invokersHashCode = invokers.hashCode();
-        ConsistentHashSelector<T> selector = (ConsistentHashSelector<T>) selectors.get(key);
-        if (selector == null || selector.identityHashCode != invokersHashCode) {
-            selectors.put(key, new ConsistentHashSelector<T>(invokers, methodName, invokersHashCode));
-            selector = (ConsistentHashSelector<T>) selectors.get(key);
-        }
+        // using the hashcode of invoker list to create consistent selector by atomic computation.
+        ConsistentHashSelector<T> selector = (ConsistentHashSelector<T>) selectors.compute(
+                key,
+                (k, oldSelector) -> (oldSelector == null || oldSelector.identityHashCode != invokersHashCode)
+                        ? new ConsistentHashSelector<>(invokers, methodName, invokersHashCode)
+                        : oldSelector);
         return selector.select(invocation);
     }