In complex application quite often you end up having a view that takes ages to load because some parts of view require heavy computation. If you are pursuing the goal of making your application responsive, you would probably want to defer updates for these parts. It's quite tempting to use UI.access() for that:

...
ui.access(() -> {
    SomeData result = doHeavyLifting();
    showData(result);
});

While it will make load time much faster, there is a problem there: since the UI is blocked by computation thread, user will have to wait for it to finish before his actions will be processed. That is, he will see the same loading indicator if he, for example, click some button that has server side click listener.

Practically that means that you have to create a worker thread yourself and then call UI.accessSynchronously() when done:

Thread workerThread = new Thread(() -> {
    SomeData result = doHeavyLifting();
    ui.accessSynchronously(() -> showData(result));
});
workerThread.start();

That will work with Push out of the box. However, if you don't have Push enabled, you'll have to call ui.setPollingInterval() to enable polling:

ui.setPollingInterval(200);
Thread workerThread = new Thread(() -> {
    SomeData result = doHeavyLifting();
    ui.accessSynchronously(() -> {
        showData(result);
        ui.setPollingInterval(-1); // Disable polling afterwards
    });
});
workerThread.start();

Now we have another tiny problem: we need to clear polling interval if the user is leaving the view before thread finishes:

ui.setPollingInterval(200);
Thread workerThread = new Thread(() -> {
    SomeData result = doHeavyLifting();
    ui.accessSynchronously(() -> {
        showData(result);
        ui.setPollingInterval(-1); // Disable polling afterwards
    });
});
workerThread.start();
addBeforeLeaveListener(event -> ui.setPollingInterval(-1));

See how easy our 4 line snippet turns to 10 line monster? And what if we have several of those worker threads? Moreover, even if we have push enabled, something should terminate threads when their results are not needed anymore (i.e. user has left the view).

But wander no more, there is an easy solution: Async Manager. It is really easy to use:

AsyncManager.register(this, task -> {
    SomeData result = doHeavyLifting();
    task.push(() -> showData(result));
})

AsyncManager supports both push and polling, and takes care of cleanup and thread termination. For polling mode it also supports dynamic polling intervals: i.e. you can have 5 polls per second in the first second and then throttle it to send poll requests once per second:

AsyncManager.getInstance().setPollingIntervals(200, 200, 200, 200, 200, 1000);

It is also possible to set custom exception handler if you want some custom logging or exception reporting:

AsyncManager.getInstance().setExceptionHandler((task, exception) -> ...);

Note: By default all worker threads are started by ThreadPoolExecutor which defaults to pool size of 25 threads. You can change that with AsyncManager.getInstance().setExecutorService().

<repository>
   <id>vaadin-addons</id>
   <url>http://maven.vaadin.com/vaadin-addons</url>
</repository>

<dependency>
   <groupId>org.vaadin.helper</groupId>
   <artifactId>async-manager</artifactId>
   <version>1.1.0-alpha1</version>
</dependency>

Starting the test/demo server:

mvn jetty:run

This deploys demo at http://localhost:8080