异步无法在游戏中运行2.1

Question

I have been wanting to test the async methods. I just couldn't understand - for every async that is called, is a new thread assigned to it or do they go into a queue in one thread.

So wanted to test it but got strange results. code:

    // block request and current thread
    public static Result syncFreeze() {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                System.in));
        String a = null;
        try {
            System.out.println("sync freeze " + Thread.activeCount()
                    + " threads running with active thread name "
                    + Thread.currentThread().getName());
            a = reader.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return ok(a);
    }

    // block request but should keep thread open
    public static Result asyncFreeze() {
        Promise<String> promiseOfString = play.libs.Akka.future(new Reader());
        return async(promiseOfString.map(new Function<String, Result>() {
            public Result apply(String s) {
                return ok(s);
            }
        }));
    }

    static class Reader implements Callable<String> {
        public String call() {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    System.in));
            String a = null;
            System.out.println("Async freeze " + Thread.activeCount()
                    + " threads running with active thread name "
                    + Thread.currentThread().getName());
            try {
                a = reader.readLine();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return a;
        }
    }

I thought that if the asyncFreeze was called, that this would never block the thread handling http requests. But it does not perform any differently then syncFreeze(). For both methods, - once called eight times, no other page can be loaded - showing that all threads serving requests have been blocked. But this does not make sense to me - that was supposed to be the whole point of the async() method. It should allow the main thread handling requests to continue. All talked about here .

What am I doing wrong?

Thanks a lot

(Suggested Edit) - how I tested it:

I simply reloaded the browser directed to the sync and async methods. For every call the method locks until input from terminal -. At first I do not unblock it. I simply keep reloading the call to sync() or async() whilst in another browser window I try to load an index() page. Eventually (actually after eight calls to sync()/async()) all threads are blocked and index() does not load - until I unblock the thread by pressing enter on the terminal window.

Answer 1

This should explain all the things that you'd like to know: http://www.playframework.com/documentation/2.2.x/ThreadPools

Shortly, it's not a thread-per-request model. Play uses Akka which is an implementation of a reactive programming principles. Oversimplified - there is a thread pool (or more of them) and once all threads of that pool are busy, then nothing else is executed. If you have a blocking code then there are ways how to deal with it explained in the article.