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    <p>When you use await in a controller it does bytecode enhancement to break a single method into two threads. This is pretty cool, but definitely one of the 'black magic' tricks of Play1. But, this is one place where Play often acts weird and requires a restart (or as you found, some code changing) - the other place it can act strange is when you change a Model class. </p> <p><a href="http://www.playframework.com/documentation/1.2.5/asynchronous#SuspendingHTTPrequests" rel="nofollow">http://www.playframework.com/documentation/1.2.5/asynchronous#SuspendingHTTPrequests</a></p> <blockquote> <p>To make it easier to deal with asynchronous code we have introduced continuations. Continuations allow your code to be suspended and resumed transparently. So you write your code in a very imperative way, as:</p> <p>public static void computeSomething() { Promise delayedResult = veryLongComputation(…); String result = await(delayedResult); render(result); } </p> <p>In fact here, your code will be executed in 2 steps, in 2 different hreads. But as you see it, it’s very transparent for your application code.</p> <p>Using await(…) and continuations, you could write a loop:</p> </blockquote> <pre><code> public static void loopWithoutBlocking() { for(int i=0; i&lt;=10; i++) { Logger.info(i); await("1s"); } renderText("Loop finished"); } </code></pre> <blockquote> <p>And using only 1 thread (which is the default in development mode) to process requests, Play is able to run concurrently these loops for several requests at the same time.</p> </blockquote> <hr> <p>To respond to your comment: </p> <pre><code> public static void generatePDF(Long reportId) { Promise&lt;InputStream&gt; pdf = new ReportAsPDFJob(report).now(); InputStream pdfStream = await(pdf); renderBinary(pdfStream); </code></pre> <p>and ReportAsPDFJob is simply a play Job class with doJobWithResult overridden - so it returns the object. See <a href="http://www.playframework.com/documentation/1.2.5/jobs" rel="nofollow">http://www.playframework.com/documentation/1.2.5/jobs</a> for more on jobs. </p> <p>Calling <code>job.now()</code> returns a future/promise, which you can use like this: <code>await(job.now())</code></p>
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    1. POPlay Framework await() makes the application act wierd
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    1. USTom Carchrae
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    1. COGreat, I came up with the same conclusion, and I could have not described it better than play's black magic. Your workaround seems interesting, however if I am waiting here for an object to be ready, how can I control that? await(1s) until promiseObject.isDone?
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      1. USRicardo Mogg
    2. COif you want to wait on something to return, then use Job with result. i'll update the answer.
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    3. COhope that edit helps. but the main issue in this question is how play auto-recompilation happens when you are developing. i would say, it just sometimes breaks - knowing on what/why just helps you know when you need to restart play.
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