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POasync / await - am I correctly running these methods in parallel?
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  1. POasync / await - am I correctly running these methods in parallel?
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    copied!<p>I have an abstract class called <code>VehicleInfoFetcher</code> which returns information asynchronously from a <code>WebClient</code> via this method:</p> <pre><code>public override async Task&lt;DTOrealtimeinfo&gt; getVehicleInfo(string stopID); </code></pre> <p>I'd like to combine the results of two separate instances of this class, running each in parallel before combining the results. This is done within a third class, <code>CombinedVehicleInfoFetcher</code> (also itself a subclass of <code>VehicleInfoFetcher</code>)</p> <p>Here's my code - but I'm not quite convinced that it's running the tasks in parallel; am I doing it right? Could it be optimized?</p> <pre><code> public class CombinedVehicleInfoFetcher : VehicleInfoFetcher { public HashSet&lt;VehicleInfoFetcher&gt; VehicleInfoFetchers { get; set; } public override async Task&lt;DTOrealtimeinfo&gt; getVehicleInfo(string stopID) { // Create a list of parallel tasks to run var resultTasks = new List&lt;Task&lt;DTOrealtimeinfo&gt;&gt;(); foreach (VehicleInfoFetcher fetcher in VehicleInfoFetchers) resultTasks.Add(fetcher.getVehicleInfo(stopID, stopID2, timePointLocal)); // run each task foreach (var task in resultTasks) await task; // Wait for all the results to come in await Task.WhenAll(resultTasks.ToArray()); // combine the results var allRealtimeResults = new List&lt;DTOrealtimeinfo&gt;( resultTasks.Select(t =&gt; t.Result) ); return combineTaskResults(allRealtimeResults); } DTOrealtimeinfo combineTaskResults(List&lt;DTOrealtimeinfo&gt; realtimeResults) { // ... return rtInfoOutput; } } </code></pre> <p><strong>Edit</strong> </p> <p>Some very helpful answers, here is a re-written example to aid discussion with usr below:</p> <pre><code> public override async Task&lt;object&gt; combineResults() { // Create a list of parallel tasks to run var resultTasks= new List&lt;object&gt;(); foreach (AnotherClass cls in this.OtherClasses) resultTasks.Add(cls.getResults() ); // Point A - have the cls.getResults() methods been called yet? // Wait for all the results to come in await Task.WhenAll(resultTasks.ToArray()); // combine the results return new List&lt;object&gt;( resultTasks.Select(t =&gt; t.Result) ); } } </code></pre>
 

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