GEODE-10338: Fix LogWriterAppender shutdown (#7725)

* GEODE-10338: Fix LogWriterAppender shutdown

When a stop session is called on the LogWriterAppender, it closes the
ManagerLogWriter's files. Still, it does not release
ManagerLogWriter's reference, so the LogWriterAppender instance is
kept around after disconnect. This situation ends up keeping the
InternalDistributedSystem alive.

The fix is to clear the LogWriterAppender's reference to the
ManagerLogWriter when the appender session is stopped.

* Update after review

* Fix integration test

* Add nullptr check in stopSession()

geode-log4j/src/integrationTest/java/org/apache/geode/logging/log4j/internal/impl/LogWriterAppenderShutdownIntegrationTest.java

@@ -0,0 +1,130 @@
+/*
+ * 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.geode.logging.log4j.internal.impl;
+
+import static org.apache.geode.test.util.ResourceUtils.createFileFromResource;
+import static org.apache.geode.test.util.ResourceUtils.getResource;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import java.io.File;
+import java.net.URL;
+
+import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.junit.LoggerContextRule;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.ClassRule;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.junit.rules.TemporaryFolder;
+import org.junit.rules.TestName;
+
+import org.apache.geode.logging.internal.log4j.api.LogService;
+import org.apache.geode.logging.internal.spi.LogConfig;
+import org.apache.geode.logging.internal.spi.LogConfigSupplier;
+import org.apache.geode.logging.internal.spi.SessionContext;
+import org.apache.geode.test.junit.categories.LoggingTest;
+
+/**
+ * Integration tests for {@link LogWriterAppender}.
+ */
+@Category(LoggingTest.class)
+public class LogWriterAppenderShutdownIntegrationTest {
+
+  private static final String CONFIG_FILE_NAME = "LogWriterAppenderIntegrationTest_log4j2.xml";
+  private static final String APPENDER_NAME = "LOGWRITER";
+
+  private static String configFilePath;
+
+  private File logFile;
+
+  private String logMessage;
+
+  private Logger logger;
+
+  private LogWriterAppender logWriterAppender;
+
+  private SessionContext sessionContext;
+
+  @ClassRule
+  public static TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+  @Rule
+  public LoggerContextRule loggerContextRule = new LoggerContextRule(configFilePath);
+
+  @Rule
+  public TestName testName = new TestName();
+
+  @BeforeClass
+  public static void setUpLogConfigFile() {
+    URL resource = getResource(CONFIG_FILE_NAME);
+    configFilePath = createFileFromResource(resource, temporaryFolder.getRoot(), CONFIG_FILE_NAME)
+        .getAbsolutePath();
+  }
+
+  @Before
+  public void setUp() {
+    String name = testName.getMethodName();
+    logFile = new File(temporaryFolder.getRoot(), name + ".log");
+
+    LogConfig config = mock(LogConfig.class);
+    when(config.getName()).thenReturn(name);
+    when(config.getLogFile()).thenReturn(logFile);
+
+    LogConfigSupplier logConfigSupplier = mock(LogConfigSupplier.class);
+    when(logConfigSupplier.getLogConfig()).thenReturn(config);
+
+    sessionContext = mock(SessionContext.class);
+    when(sessionContext.getLogConfigSupplier()).thenReturn(logConfigSupplier);
+
+    logger = LogService.getLogger();
+    logMessage = "Logging in " + testName.getMethodName();
+
+    logWriterAppender =
+        loggerContextRule.getAppender(APPENDER_NAME, LogWriterAppender.class);
+  }
+
+  @Test
+  public void stopActiveSession() {
+    logWriterAppender.clearLogEvents();
+
+    logWriterAppender.createSession(sessionContext);
+    logWriterAppender.startSession();
+    assertThat(logWriterAppender.getLogWriter()).isNotNull();
+    assertThat(logWriterAppender.isStarted()).isTrue();
+
+    logger.info(logMessage);
+
+    assertThat(logWriterAppender.getLogEvents()).hasSize(1);
+    LogEvent event = logWriterAppender.getLogEvents().get(0);
+    assertThat(event.getLoggerName()).isEqualTo(getClass().getName());
+    assertThat(event.getLevel()).isEqualTo(Level.INFO);
+    assertThat(event.getMessage().getFormattedMessage()).isEqualTo(logMessage);
+
+    logWriterAppender.stopSession();
+    assertThat(logWriterAppender.getLogWriter()).isNull();
+    assertThat(logWriterAppender.isPaused()).isTrue();
+    logWriterAppender.clearLogEvents();
+
+    logger.info(logMessage);
+
+    assertThat(logWriterAppender.getLogEvents()).hasSize(0);
+  }
+}

geode-log4j/src/main/java/org/apache/geode/logging/log4j/internal/impl/LogWriterAppender.java

@@ -303,9 +303,17 @@ public synchronized void startSession() {
   @Override
   public synchronized void stopSession() {
     LOGGER.info("Stopping session in {}.", this);
-    logWriter.shuttingDown();
-    pause();
-    logWriter.closingLogFile();
+    if (logWriter == null) {
+      pause();
+      return;
+    }
+    try {
+      logWriter.shuttingDown();
+      pause();
+      logWriter.closingLogFile();
+    } finally {
+      logWriter = null;
+    }
   }
 
   @Override