[JENKINS-72796] stable context classloader for Computer.threadPoolForRemoting

core/src/main/java/hudson/model/Computer.java

@@ -63,6 +63,7 @@
 import hudson.slaves.RetentionStrategy;
 import hudson.slaves.WorkspaceList;
 import hudson.triggers.SafeTimerTask;
+import hudson.util.ClassLoaderSanityThreadFactory;
 import hudson.util.DaemonThreadFactory;
 import hudson.util.EditDistance;
 import hudson.util.ExceptionCatchingThreadFactory;
@@ -1381,7 +1382,9 @@ public String call() throws IOException {
                 Executors.newCachedThreadPool(
                     new ExceptionCatchingThreadFactory(
                         new NamingThreadFactory(
-                            new DaemonThreadFactory(), "Computer.threadPoolForRemoting")))), ACL.SYSTEM2));
+                            new ClassLoaderSanityThreadFactory(new DaemonThreadFactory()),
+                            "Computer.threadPoolForRemoting")))),
+            ACL.SYSTEM2));
 
 //
 //

core/src/test/java/hudson/model/ComputerTest.java

@@ -8,9 +8,11 @@
 import hudson.FilePath;
 import hudson.security.ACL;
 import java.io.File;
+import java.util.ArrayList;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 import jenkins.model.Jenkins;
+import jenkins.util.SetContextClassLoader;
 import org.junit.Test;
 import org.jvnet.hudson.test.Issue;
 import org.springframework.security.core.Authentication;
@@ -45,4 +47,42 @@ public void testThreadPoolForRemotingActsAsSystemUser() throws InterruptedExcept
         Future<Authentication> job = Computer.threadPoolForRemoting.submit(Jenkins::getAuthentication2);
         assertThat(job.get(), is(ACL.SYSTEM2));
     }
+
+    @Issue("JENKINS-72796")
+    @Test
+    public void testThreadPoolForRemotingContextClassLoaderIsSet() throws Exception {
+        // as the threadpool is cached, any other tests here pollute this test so we need enough threads to
+        // avoid any cached.
+        final int numThreads = 5;
+
+        // simulate the first call to Computer.threadPoolForRemoting with a non default classloader
+        try (var ignored = new SetContextClassLoader(new ClassLoader() {})) {
+            obtainAndCheckThreadsContextClassloaderAreCorrect(numThreads);
+        }
+        // now repeat this as the checking that the pollution of the context classloader is handled
+        obtainAndCheckThreadsContextClassloaderAreCorrect(numThreads);
+    }
+
+    private static void obtainAndCheckThreadsContextClassloaderAreCorrect(int numThreads) throws Exception {
+        ArrayList<Future<ClassLoader>> classloaderFuturesList = new ArrayList<>();
+        // block all calls to getContextClassloader() so we create more threads.
+        synchronized (WaitAndGetContextClassLoader.class) {
+            for (int i = 0; i < numThreads; i++) {
+                classloaderFuturesList.add(Computer.threadPoolForRemoting.submit(WaitAndGetContextClassLoader::getContextClassloader));
+            }
+        }
+        for (Future<ClassLoader> fc : classloaderFuturesList) {
+            assertThat(fc.get(), is(Jenkins.class.getClassLoader()));
+        }
+    }
+
+    private static class WaitAndGetContextClassLoader {
+
+        public static synchronized ClassLoader getContextClassloader() throws InterruptedException {
+            ClassLoader ccl = Thread.currentThread().getContextClassLoader();
+            // intentionally pollute the Threads context classloader
+            Thread.currentThread().setContextClassLoader(new ClassLoader() {});
+            return ccl;
+        }
+    }
 }