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POAysnc/Await Vs. Task/Continuation UI Control Access
 

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    <p>All, I have a situation where I have been asked to multi-thread a large 'Cost-Crunching' algorithm. I am relatively experienced with <code>Task</code>s and would be confident in adopting a pattern like </p> <pre><code>CancellationTokenSource cancelSource = new CancellationTokenSource(); CancellationToken token = cancelSource.Token; TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); Task&lt;bool&gt; asyncTask = null; asyncTask = Task.Factory.StartNew&lt;bool&gt;(() =&gt; SomeMethodAsync(uiScheduler, token, _dynamic), token); asyncTask.ContinueWith(task =&gt; { // For call back, exception handling etc. }, uiScheduler); </code></pre> <p>and then for any operation where I need to provide and UI operation, I would use </p> <pre><code>Task task = Task.Factory.StartNew(() =&gt; { mainForm.progressLeftLabelText = _strProgressLabel; }, CancellationToken.None, TaskCreationOptions.None, uiScheduler); </code></pre> <p>Where this might be wrapped up in a method.</p> <p>Now, I realise that I can make all this much less complicated, and leverage the <code>async/await</code> keywords of .NET 4.5. However, I have some questions: if I have a long running method that I launch using </p> <pre><code>// Start processing asynchroniously. IProgress&lt;CostEngine.ProgressInfo&gt; progressIndicator = new Progress&lt;CostEngine.ProgressInfo&gt;(); cancelSource = new CancellationTokenSource(); CancellationToken token = cancelSource.Token; CostEngine.ScriptProcessor script = new CostEngine.ScriptProcessor(this); await script.ProcessScriptAsync(doc, progressIndicator, token); </code></pre> <p>where <code>CostEngine.ProgressInfo</code> is some basic class used to return progress information and the method <code>ProcessScriptAsync</code> is defined as </p> <pre><code>public async Task ProcessScriptAsync(SSGForm doc, IProgress&lt;ProgressInfo&gt; progressInfo, CancellationToken token, bool bShowCompleted = true) { ... if (!await Task&lt;bool&gt;.Run(() =&gt; TheLongRunningProcess(doc))) return ... } </code></pre> <hr> <p>I have two questions:</p> <ol> <li><p>To get <code>ProcessScriptAsync</code> to return control to the UI <em>almost</em> immediately I await on a new <code>Task&lt;bool&gt;</code> delegate (this seemingly avoids an endless chain of <code>async</code>/<code>await</code>s). <strong>Is this the right way to call <code>ProcessScriptAsync</code>?</strong> ['Lazy Initialisation', by wrapping in an outer method?]</p></li> <li><p>To access the UI from within <code>TheLongRunningProcess</code>, do I merely pass in the UI <code>TaskScheduler</code> <code>uiScheduler</code>; i.e. <code>TheLongRunningProcess(doc, uiScheduler)</code>, then use:</p></li> </ol> <hr> <pre><code>Task task = Task.Factory.StartNew(() =&gt; { mainForm.progressLeftLabelText = _strProgressLabel; }, CancellationToken.None, TaskCreationOptions.None, uiScheduler); </code></pre> <p>as before?</p> <p>Sorry about the length and thanks for your time.</p>
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    1. COSince you have two questions they really should be asked in two different questions, not one.
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    2. COBut that would mean replicating most of the question. I always think/worry about this, but it seems overkill to replicate what is above the line when the questions are so heavily related...
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    3. COMeh. Most of this doesn't really apply to the second question and doesn't need to be there. It also allows you to get an answer to one question but not the other, should someone know the answer to only one. If you ask both, you limit responses to people who know the answer to both.
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