From 354e7b147eb00efeb24119225039e577627cab39 Mon Sep 17 00:00:00 2001
From: dajiaohuang <mikewushuwen@outlook.com>
Date: Sun, 25 Oct 2026 12:40:34 +0800
Subject: [PATCH] [POOL-432] Guard monitor recovery when no adder exists

Generated-by: OpenAI Codex gpt-6-luna
---
 .../impl/ResilientPooledObjectFactory.java    |  6 +++--
 .../TestResilientPooledObjectFactory.java     | 26 +++++++++++++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/main/java/org/apache/commons/pool3/impl/ResilientPooledObjectFactory.java b/src/main/java/org/apache/commons/pool3/impl/ResilientPooledObjectFactory.java
index 53f5ea0bf..c1ca2d39c 100644
--- a/src/main/java/org/apache/commons/pool3/impl/ResilientPooledObjectFactory.java
+++ b/src/main/java/org/apache/commons/pool3/impl/ResilientPooledObjectFactory.java
@@ -479,8 +479,10 @@ protected void runChecks() {
             // Kill adder thread and set up to true
             upStart = Instant.now();
             up = true;
-            adder.kill();
-            adder = null;
+            if (adder != null) {
+                adder.kill();
+                adder = null;
+            }
         }
     }
 
diff --git a/src/test/java/org/apache/commons/pool3/impl/TestResilientPooledObjectFactory.java b/src/test/java/org/apache/commons/pool3/impl/TestResilientPooledObjectFactory.java
index 242106c0f..35ee5058d 100644
--- a/src/test/java/org/apache/commons/pool3/impl/TestResilientPooledObjectFactory.java
+++ b/src/test/java/org/apache/commons/pool3/impl/TestResilientPooledObjectFactory.java
@@ -16,8 +16,10 @@
  */
 package org.apache.commons.pool3.impl;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.time.Duration;
@@ -257,6 +259,30 @@ public void run() {
         assertFalse(rf.isMonitorRunning());
     }
 
+    @Test
+    void testRecoveryWithoutAdderDoesNotThrowWhenFactoryComesBackUp() throws Exception {
+        final FailingFactory ff = new FailingFactory();
+        ff.setSilentFail(false);
+        final ResilientPooledObjectFactory<String, Exception> rf = new ResilientPooledObjectFactory<>(ff,
+                2, Duration.ofMillis(10), Duration.ofMinutes(10), Duration.ofMillis(10));
+        final GenericObjectPool<String, Exception> pool = new GenericObjectPool<>(rf);
+        rf.setPool(pool);
+
+        ff.crash();
+        assertThrows(Exception.class, rf::makeObject);
+        rf.runChecks();
+        assertFalse(rf.isUp());
+        assertFalse(rf.isAdderRunning());
+
+        ff.recover();
+        rf.makeObject();
+        rf.makeObject();
+        assertDoesNotThrow(rf::runChecks);
+        assertTrue(rf.isUp());
+        assertFalse(rf.isAdderRunning());
+        pool.close();
+    }
+
     @Test
     void testTransientFailure() throws Exception {
         final FailingFactory ff = new FailingFactory();