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POGuava : setting the default Executor for ListenableFuture callbacks and listeners
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  1. POGuava : setting the default Executor for ListenableFuture callbacks and listeners
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    copied!<p>Our application has a number of services that implement <code>ListenableFuture</code>-based APIs, to the tune of:</p> <pre><code>public interface MyService { ListenableFuture&lt;Thing&gt; getMyThing(); ListenableFuture&lt;?&gt; putMyThing(Thing thing); } </code></pre> <p>As our domain model is not at all thread-safe, we run most of our code, except for the aforementioned services, on a well-known single-thread <code>Executor</code>. I think it would be nice if the services could guarantee that any listener added to the <code>Future</code>s they produce will be called on that <code>Executor</code>.</p> <p>Of course, I could very well enforce this in the services' clients, by calling <code>ListenableFuture.addListener</code>, <code>Futures.addCallback</code> or <code>Futures.transform</code> with the appropriate <code>Executor</code> argument but what I'm aiming at is precisely reducing the complexity and possibility of errors in the client code, so I would like the listener calls to happen on the well-known <code>Executor</code> when those methods are called without passing an <code>Executor</code> argument.</p> <p>So, for now I've been implementing the services' methods this way:</p> <pre><code>class MyServiceImpl { private Executor executor; /* the "main" executor */ public ListenableFuture&lt;Thing&gt; getMyThing() { ListenableFuture&lt;Thing&gt; future = ...; /* actual service call */ return Futures.transform(future, Functions.&lt;Thing&gt;identity(), executor ); } } </code></pre> <p>First, does this even work? From the Guava source, it seems that it does, but I would be glad for some kind of confirmation, and I'm having a bit of a hard time thinking about unit testing this.</p> <p>Moreover, I'm a bit worried about the usefulness/cost ratio of the whole "Service calls back on specified thread (by default)" pattern. Does anyone have experience with something like this? Are there any hidden pitfalls in this approach?</p>
 

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