Double-check before closing

Author: eric-zc1

trpc-core/src/main/java/com/tencent/trpc/core/cluster/RpcClusterClientManager.java

@@ -123,11 +123,32 @@ public static void scanUnusedClient() {
         });
         unusedClientMap.forEach((bConfig, value) -> value.forEach(e -> {
             try {
+                RpcClientProxy proxy = (RpcClientProxy) e;
+                // Double-check before closing: ensure the client is still idle to avoid closing a client in use.
+                // This prevents race condition where getOrCreateClient() gets a client right before it's closed.
+                if (!isIdleTimeout(bConfig, proxy)) {
+                    // lastUsedNanos was updated, meaning a business thread is using it, try to put it back
+                    Map<String, RpcClientProxy> clientMap = CLUSTER_MAP.get(bConfig);
+                    if (clientMap != null) {
+                        RpcClientProxy existing = clientMap.putIfAbsent(
+                                proxy.getProtocolConfig().toUniqId(), proxy);
+                        if (existing == null) {
+                            // Successfully put back, do not close
+                            logger.info("RpcClient {} rescued from closing due to recent usage",
+                                    proxy.getProtocolConfig().toSimpleString());
+                            return;
+                        }
+                    }
+                    // Failed to put back (a new client already exists), still need to close the old one
+                }
                 e.close();
-            } finally {
                 logger.warn("RpcClient in clusterName={}, naming={}, remove rpc client{}, due to unused time > {} ms",
                         bConfig.getName(), bConfig.getNamingOptions().getServiceNaming(),
                         e.getProtocolConfig().toSimpleString(), bConfig.getIdleTimeout());
+            } catch (Exception ex) {
+                logger.error("Failed to close RpcClient in clusterName={}, naming={}, client={}",
+                        bConfig.getName(), bConfig.getNamingOptions().getServiceNaming(),
+                        e.getProtocolConfig().toSimpleString(), ex);
             }
         }));
     }
@@ -322,4 +343,4 @@ public boolean equals(Object obj) {
         }
     }
 
-}
+}