add a thread factory that names the threads

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

@@ -36,7 +36,9 @@ public abstract class JarCacheSupport extends JarCache {
     /**
      * Throttle the jar downloading activity so that it won't eat up all the channel bandwidth.
      */
-    private final ExecutorService downloader = new AtmostOneThreadExecutor();
+    private final ExecutorService downloader = new AtmostOneThreadExecutor(
+            new NamingThreadFactory(new DaemonThreadFactory(), JarCacheSupport.class.getSimpleName())
+    );
 
     @Override
     public Future<URL> resolve(final Channel channel, final long sum1, final long sum2) throws IOException, InterruptedException {

src/main/java/hudson/remoting/NamingThreadFactory.java

@@ -0,0 +1,56 @@
+/*
+ * The MIT License
+ *
+ * Copyright 2013 Jesse Glick.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package hudson.remoting;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * Thread factory that sets thread name so we know who is responsible for so many threads being created.
+ * @since FIXME after merge
+ */
+public class NamingThreadFactory implements ThreadFactory {
+    private final AtomicInteger threadNum = new AtomicInteger();
+    private final ThreadFactory delegate;
+    private final String name;
+
+    /**
+     * Creates a new naming factory.
+     * @param delegate a baseline factory, such as {@link Executors#defaultThreadFactory} or {@link DaemonThreadFactory}
+     * @param name an identifier to be used in thread names; might be e.g. your {@link Class#getSimpleName}
+     */
+    public NamingThreadFactory(ThreadFactory delegate, String name) {
+        this.delegate = delegate;
+        this.name = name;
+    }
+
+    @Override
+    public Thread newThread(Runnable r) {
+        Thread result = delegate.newThread(r);
+        result.setName(String.format("%s [#%d]", name, threadNum.incrementAndGet()));
+        return result;
+    }
+}