Make JarCacheSupport be Closeable

Author: jglick

src/main/java/hudson/remoting/Channel.java

@@ -1611,6 +1611,9 @@ public void close(@CheckForNull Throwable diagnosis) throws IOException {
                 terminate(e);
                 return;
             }
+            if (jarCache instanceof Closeable c) {
+                c.close();
+            }
             outClosed = new IOException(
                     diagnosis); // last command sent. no further command allowed. lock guarantees that no command will
             // slip inbetween

src/main/java/hudson/remoting/JarCacheSupport.java

@@ -2,6 +2,7 @@
 
 import edu.umd.cs.findbugs.annotations.NonNull;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+import java.io.Closeable;
 import java.io.IOException;
 import java.net.URL;
 import java.util.concurrent.CompletableFuture;
@@ -21,7 +22,7 @@
  * @author Kohsuke Kawaguchi
  * @since 2.24
  */
-public abstract class JarCacheSupport extends JarCache {
+public abstract class JarCacheSupport extends JarCache implements Closeable {
     /**
      * Remember in-progress jar file resolution to avoid retrieving the same jar file twice.
      */
@@ -75,6 +76,12 @@ private CompletableFuture<URL> submitDownload(Channel channel, long sum1, long s
         return promise;
     }
 
+    @Override
+    public void close() throws IOException {
+        // TODO Java 21 maybe just use ExecutorService.close()
+        downloader.shutdown();
+    }
+
     private class DownloadRunnable implements Runnable {
 
         final Channel channel;