If an exception occurs while launching an agent, the underlying conne…

…ction and session should be closed

Observed the following stacktrace when running a controller using JDK17
bytecode level, and having an agent template still configured with a
JDK11. The agent initially connects fine, however as soon as it attempts
to do remote classloading, it fails.

As it occurs while setting up the hudson.remoting.Channel itself, the
listener that is registered during initialization is never called, and
the exception handling block should instead close the underlying
resources.

2024-10-18 02:48:21.686+0000 [id=593]	WARNING	c.g.j.p.c.ComputeEngineCloud#log: Error:
java.lang.UnsupportedClassVersionError: hudson/slaves/SlaveComputer$SlaveVersion has been compiled by a more recent version of the Java Runtime (class file version 61.0), this version of the Java Runtime only recognizes class file versions up to 55.0
	at java.base/java.lang.ClassLoader.defineClass1(Native Method)
	at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017)
	at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:878)
	at hudson.remoting.RemoteClassLoader.loadClassFile(RemoteClassLoader.java:470)
Also:   hudson.remoting.Channel$CallSiteStackTrace: Remote call to gce-cloud-gauntlet3-gaia-jdk11-t4dx04
		at hudson.remoting.Channel.attachCallSiteStackTrace(Channel.java:1923)
		at hudson.remoting.UserRequest$ExceptionResponse.retrieve(UserRequest.java:384)
		at hudson.remoting.Channel.call(Channel.java:1112)
		at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:663)
		at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:441)
		at PluginClassLoader for google-compute-engine//com.google.jenkins.plugins.computeengine.ComputeEngineComputerLauncher.launch(ComputeEngineComputerLauncher.java:303)
		at PluginClassLoader for google-compute-engine//com.google.jenkins.plugins.computeengine.ComputeEngineComputerLauncher.launch(ComputeEngineComputerLauncher.java:214)
		at hudson.slaves.SlaveComputer.lambda$_connect$0(SlaveComputer.java:297)
		at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46)
		at jenkins.security.ImpersonatingExecutorService$2.call(ImpersonatingExecutorService.java:80)
		at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
		at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
		at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
		at java.base/java.lang.Thread.run(Thread.java:840)
Caused: java.lang.UnsupportedClassVersionError: Failed to load hudson.slaves.SlaveComputer$SlaveVersion
	at hudson.remoting.RemoteClassLoader.loadClassFile(RemoteClassLoader.java:472)
	at hudson.remoting.RemoteClassLoader.loadRemoteClass(RemoteClassLoader.java:301)
	at hudson.remoting.RemoteClassLoader.loadWithMultiClassLoader(RemoteClassLoader.java:277)
	at hudson.remoting.RemoteClassLoader.findClass(RemoteClassLoader.java:236)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:589)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
	at java.base/java.lang.Class.forName0(Native Method)
	at java.base/java.lang.Class.forName(Class.java:398)
	at hudson.remoting.MultiClassLoaderSerializer$Input.resolveClass(MultiClassLoaderSerializer.java:133)
	at java.base/java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:2003)
	at java.base/java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1870)
	at java.base/java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2201)
	at java.base/java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1687)
	at java.base/java.io.ObjectInputStream.readObject(ObjectInputStream.java:489)
	at java.base/java.io.ObjectInputStream.readObject(ObjectInputStream.java:447)
	at hudson.remoting.UserRequest.deserialize(UserRequest.java:312)
	at hudson.remoting.UserRequest.perform(UserRequest.java:196)
	at hudson.remoting.UserRequest.perform(UserRequest.java:50)
	at hudson.remoting.Request$2.run(Request.java:391)
	at hudson.remoting.InterceptingExecutorService.lambda$wrap$0(InterceptingExecutorService.java:81)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:829)
Caused: java.io.IOException: Remote call on gce-cloud-gauntlet3-gaia-jdk11-t4dx04 failed
	at hudson.remoting.Channel.call(Channel.java:1116)
	at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:663)
	at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:441)
	at PluginClassLoader for google-compute-engine//com.google.jenkins.plugins.computeengine.ComputeEngineComputerLauncher.launch(ComputeEngineComputerLauncher.java:303)
	at PluginClassLoader for google-compute-engine//com.google.jenkins.plugins.computeengine.ComputeEngineComputerLauncher.launch(ComputeEngineComputerLauncher.java:214)
	at hudson.slaves.SlaveComputer.lambda$_connect$0(SlaveComputer.java:297)
	at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46)
	at jenkins.security.ImpersonatingExecutorService$2.call(ImpersonatingExecutorService.java:80)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:840)

src/main/java/com/google/jenkins/plugins/computeengine/ComputeEngineComputerLauncher.java

@@ -280,10 +280,11 @@ private void launch(ComputeEngineComputer computer, TaskListener listener) {
             return;
         }
 
-        final Connection conn;
+        Connection conn = null;
         Optional<Connection> cleanupConn;
         PrintStream logger = listener.getLogger();
         logInfo(computer, listener, "Launching instance: " + node.getNodeName());
+        Session sess = null;
         try {
             cleanupConn = setupConnection(node, computer, listener);
             if (!cleanupConn.isPresent()) {
@@ -298,16 +299,24 @@ private void launch(ComputeEngineComputer computer, TaskListener listener) {
             copyAgentJar(computer, conn, listener, jenkinsDir);
             String launchString = getJavaLaunchString(javaExecPath, jenkinsDir);
             logInfo(computer, listener, "Launching Jenkins agent via plugin SSH: " + launchString);
-            final Session sess = conn.openSession();
+            sess = conn.openSession();
             sess.execCommand(launchString);
+            Session finalSess = sess;
+            Connection finalConn = conn;
             computer.setChannel(sess.getStdout(), sess.getStdin(), logger, new Channel.Listener() {
                 @Override
                 public void onClosed(Channel channel, IOException cause) {
-                    sess.close();
-                    conn.close();
+                    finalSess.close();
+                    finalConn.close();
                 }
             });
         } catch (Exception e) {
+            if (sess != null) {
+                sess.close();
+            }
+            if (conn != null) {
+                conn.close();
+            }
             logException(computer, listener, "Error: ", e);
         }
     }