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POCorrect Implementation of Java Future multithreading
 

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  1. POCorrect Implementation of Java Future multithreading
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    <p>In my servlet I am hitting several URL's to check their status and returning the response to user.</p> <p>Hitting multipe requests takes lot of time: need threads and timouts. But i need my threads to geturn response : using Future for that reason.</p> <p>My code outline: </p> <pre><code>ExecutorService executor = Executors.newFixedThreadPool(10); Future&lt;statusModel&gt; future; for (Map.Entry&lt;String, String&gt; url : urls.entrySet()) { try { future = executor.submit(new CallableRequestStatus(url.getValue())); status = (statusModel) future.get(5, TimeUnit.SECONDS); results.add(status); } catch (InterruptedException | ExecutionException | TimeoutException e) { System.out.println("Error&lt;checkServers&gt;: Timeout OR "+e.getMessage()); } } executor.shutdownNow(); </code></pre> <p>All the results from my callable class is coming in status object which I later add to an arraylist. My problem here is that my approach is blocking me from running all 10 threads at same time. I have to wait 5 secs for getting my status object and then move to next URL.</p> <p>I am thinking my approach is faulty. I tried looking online but I couldnt find any example with custom objects and Arraylist involved.</p> <p>Can anyone help me correct my fault. Thanks in advance</p> <p>Finally Updated my code (thanks to Sotirios Delimanolis and Kevin):</p> <pre><code>ExecutorService executor = Executors.newFixedThreadPool(20); List&lt;Future&lt;statusModel&gt;&gt; futures = new ArrayList&lt;Future&lt;statusModel&gt;&gt;(); for (Map.Entry&lt;String, String&gt; url : urls.entrySet()) { Future&lt;statusModel&gt; future = executor.submit(new CallableRequestStatus(url.getValue())); futures.add(future); } ArrayList&lt;statusModel&gt; results = new ArrayList&lt;statusModel&gt;(); statusModel status; int i=0; for (Map.Entry&lt;String, String&gt; url : urls.entrySet()) { try { status = (statusModel) futures.get(i).get(500, TimeUnit.MILLISECONDS); // do some stuff with status and if(status.getStatusCode()/100 == 2) results.add(status); } catch (InterruptedException | ExecutionException | TimeoutException e) { System.out.println("Error&lt;checkServers&gt;: Timeout OR "+e.getMessage()); } i++; } executor.shutdownNow(); System.out.println("Shutdown: "+executor.isShutdown()); </code></pre> <p>Hope its helpful for someone :)</p>
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    1. USRahul Dabas
    1. USRahul Dabas
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    1. COAdd all the futures to a Set or List. After you've submitted all your callables, loop through the `Future` elements and call `get` without a timeout value. Your main thread will block, but the other tasks will keep executing. You'll basically wait for the duration of the longest lasting callable.
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      1. POCorrect Implementation of Java Future multithreading
      1. USSotirios Delimanolis
    2. COThanks Sotirios for quick reply. I tried what you suggested but I am still getting stuck when I loop on futureList for servers that are taking too much time.
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      1. POCorrect Implementation of Java Future multithreading
      1. USRahul Dabas
    3. COIf you need to wait for all servers to respond and get all their results, this is the only synchronous way of doing it.
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      1. POCorrect Implementation of Java Future multithreading
      1. USSotirios Delimanolis
 

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