Fix NPE in ConfigurationScheduler by ensuring scheduledFuture is chec…

log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/ConfigurationSchedulerTest.java

@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.logging.log4j.core.config;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Date;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import org.apache.logging.log4j.core.util.CronExpression;
+import org.junit.jupiter.api.Test;
+
+class ConfigurationSchedulerTest {
+    @Test
+    void testScheduleWithCronRaceCondition() throws Exception {
+        ConfigurationScheduler scheduler = new ConfigurationScheduler();
+        scheduler.incrementScheduledItems();
+        scheduler.start();
+        CronExpression cron = new CronExpression("* * * * * ?");
+        CountDownLatch latch = new CountDownLatch(1);
+        Runnable task = latch::countDown;
+        scheduler.scheduleWithCron(cron, new Date(), task);
+        assertTrue(latch.await(2, TimeUnit.SECONDS), "Task did not run in time");
+        scheduler.stop(1, TimeUnit.SECONDS);
+    }
+}

log4j-core/src/main/java/org/apache/logging/log4j/core/config/ConfigurationScheduler.java

@@ -147,13 +147,15 @@ public CronScheduledFuture<?> scheduleWithCron(final CronExpression cronExpressi
     public CronScheduledFuture<?> scheduleWithCron(
             final CronExpression cronExpression, final Date startDate, final Runnable command) {
         final Date fireDate = cronExpression.getNextValidTimeAfter(startDate == null ? new Date() : startDate);
+        final CronScheduledFuture<?>[] placeholder = new CronScheduledFuture<?>[1];
         final CronRunnable runnable = new CronRunnable(command, cronExpression);
+        placeholder[0] = new CronScheduledFuture<>(null, fireDate);
+        runnable.setScheduledFuture(placeholder[0]);
         final ScheduledFuture<?> future = schedule(runnable, nextFireInterval(fireDate), TimeUnit.MILLISECONDS);
-        final CronScheduledFuture<?> cronScheduledFuture = new CronScheduledFuture<>(future, fireDate);
-        runnable.setScheduledFuture(cronScheduledFuture);
+        placeholder[0].reset(future, fireDate);
         LOGGER.debug(
                 "{} scheduled cron expression {} to fire at {}", name, cronExpression.getCronExpression(), fireDate);
-        return cronScheduledFuture;
+        return placeholder[0];
     }
 
     /**
@@ -231,7 +233,8 @@ public void setScheduledFuture(final CronScheduledFuture<?> future) {
         @Override
         public void run() {
             try {
-                final long millis = scheduledFuture.getFireTime().getTime() - System.currentTimeMillis();
+                Date fireTime = (scheduledFuture != null) ? scheduledFuture.getFireTime() : null;
+                long millis = (fireTime != null) ? (fireTime.getTime() - System.currentTimeMillis()) : 0L;
                 if (millis > 0) {
                     LOGGER.debug("{} Cron thread woke up {} millis early. Sleeping", name, millis);
                     try {
@@ -251,13 +254,18 @@ public void run() {
                         name,
                         cronExpression.getCronExpression(),
                         fireDate);
-                scheduledFuture.reset(future, fireDate);
+                if (scheduledFuture != null) {
+                    scheduledFuture.reset(future, fireDate);
+                }
             }
         }
 
         @Override
         public String toString() {
-            return "CronRunnable{" + cronExpression.getCronExpression() + " - " + scheduledFuture.getFireTime();
+            String fireTimeStr = (scheduledFuture != null && scheduledFuture.getFireTime() != null)
+                    ? scheduledFuture.getFireTime().toString()
+                    : "unassigned";
+            return "CronRunnable{" + cronExpression.getCronExpression() + " - " + fireTimeStr + "}";
         }
     }