Google App Engine creating background thread exception

Question

I'm trying to run a long-running process in Google App Engine using Java. (basically i need something like a daemon thread? or just something runs indefinitely and doesn't block UI but can still communicate with other threads)

so i tried:

@SuppressWarnings("serial")
public class TestingAServlet extends HttpServlet {

    public void doGet(final HttpServletRequest req, final HttpServletResponse resp) throws IOException {
        resp.setContentType("text/plain");
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    resp.getWriter().println("hi, from background thread");
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        System.out.println("done");
    }
}

but i get an exception:

java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "modifyThreadGroup")

how do i make a background thread that runs indefinitely on GAE with java?

Answer 1

AppEngine doesn't allow usage of traditional threads.

You can, however, use the Modules API to spawn background tasks: https://developers.google.com/appengine/docs/java/modules/#Java_Background_threads https://developers.google.com/appengine/docs/java/javadoc/com/google/appengine/api/ThreadManager

Note that such background tasks can only be spawned on manual scaling instances.