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POHow to Cancel a PLINQ Query in a WinForms Application
 

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  1. POHow to Cancel a PLINQ Query in a WinForms Application
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    <p>I am working on application which processes large amount of text data gathering statistics on word occurrences (see: <a href="http://sourcecodecloud.codeplex.com/" rel="nofollow">Source Code Word Cloud</a>).</p> <p>Here what the simplified core of my code is doing.</p> <ol> <li>Enumerate through all files with *.txt extension.</li> <li>Enumerate through words in each text files.</li> <li>Group by word and count occurrences.</li> <li>Sort by occurrences.</li> <li>Output top 20.</li> </ol> <p>Everything worked fine with LINQ. Moving to PLINQ brought me significant performance boost. But ... cancelability during long running queries is lost.</p> <p>It seems that the OrderBy Query is synchronizing data back into main thread and windows messages are not processed.</p> <p>In the examle below I am demonstarting my implementation of cancelation according to <a href="http://msdn.microsoft.com/en-us/library/dd460707.aspx" rel="nofollow">MSDN How to: Cancel a PLINQ Query</a> whic does not work :(</p> <p>Any other ideas?</p> <pre><code>using System; using System.Collections.Generic; using System.IO; using System.Linq; using System.Text; using System.Threading; using System.Windows.Forms; namespace PlinqCancelability { public partial class Form1 : Form { public Form1() { InitializeComponent(); m_CancellationTokenSource = new CancellationTokenSource(); } private readonly CancellationTokenSource m_CancellationTokenSource; private void buttonStart_Click(object sender, EventArgs e) { var result = Directory .EnumerateFiles(@"c:\temp", "*.txt", SearchOption.AllDirectories) .AsParallel() .WithCancellation(m_CancellationTokenSource.Token) .SelectMany(File.ReadLines) .SelectMany(ReadWords) .GroupBy(word =&gt; word, (word, words) =&gt; new Tuple&lt;int, string&gt;(words.Count(), word)) .OrderByDescending(occurrencesWordPair =&gt; occurrencesWordPair.Item1) .Take(20); try { foreach (Tuple&lt;int, string&gt; tuple in result) { Console.WriteLine(tuple); } } catch (OperationCanceledException ex) { Console.WriteLine(ex.Message); } } private void buttonCancel_Click(object sender, EventArgs e) { m_CancellationTokenSource.Cancel(); } private static IEnumerable&lt;string&gt; ReadWords(string line) { StringBuilder word = new StringBuilder(); foreach (char ch in line) { if (char.IsLetter(ch)) { word.Append(ch); } else { if (word.Length != 0) continue; yield return word.ToString(); word.Clear(); } } } } } </code></pre>
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