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POWhy in C# is Queue scrambling the data in its elements?
 

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  1. POWhy in C# is Queue scrambling the data in its elements?
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    <p>I am completely perplexed with how my Queue is function. I am attempting (and failing) to write a small multi-threaded application to collect and display data in C#.<br> After reading through <a href="http://www.albahari.com/threading/" rel="nofollow noreferrer">Albahari's book</a> and using the Consumer/Producer pattern he describes I got most of it to work except my data seems to get scrambled in the queue. Before getting queued the fields in my object have the following values</p> <blockquote> <p>timeStamp = 6<br> data[] ={4936, 9845, 24125, 44861}</p> </blockquote> <p>After being dequeued the data looks like</p> <blockquote> <p>timeStamp = 6<br> data[] = {64791, 19466, 47772, 65405}</p> </blockquote> <p>I don't understand why the values in the data filed are being changed after the dequeue? I am perplexed so I thought I'd throw it out there to see if anyone can point me in the right direction to fixing this or to point me in a different direction to proceed. </p> <hr> <p><strong>Relevant Code</strong></p> <hr> <p><strong>Custom Object for data storage</strong></p> <p>Relevant objects and Fields. The class sensorData is a seperate class use to store my calculations. </p> <pre><code>public class sensorData { public const int bufSize = 4; public UInt16[] data = new UInt16[4]; public double TimeStamp = 0; public int timeIndex = 0; } </code></pre> <p>The following fields are used to setup the queue and signals between the enqueue and dequeue threads.</p> <pre><code>EventWaitHandle wh = new AutoResetEvent(false); Queue&lt;sensorData&gt; dataQ = new Queue&lt;sensorData&gt;(); object locker = new object(); </code></pre> <p><strong>Enqueue Method/Thread</strong></p> <p>This is my worker thread it calculates four Sine curves and queues the result for processing. I also write the results to a file so I know what it has calculated.</p> <pre><code>private void calculateAndEnqueueData(BackgroundWorker worker, DoWorkEventArgs e) { int j = 0; double time = 0; double dist; UInt16[] intDist = new UInt16[sensorData.bufSize]; UInt16 uint16Dist; // Frequencies of the four Sine curves double[] myFrequency = { 1, 2, 5, 10 }; // Creates the output file. StreamWriter sw2 = File.CreateText("c:\\tmp\\QueuedDataTest.txt"); // Main loop to calculate my Sine curves while (!worker.CancellationPending) { // Calculate four Sine curves for (int i = 0; i &lt; collectedData.numberOfChannels; i++) { dist = Math.Abs(Math.Sin(2.0 * Math.PI * myFrequency[i] * time); uint16Dist = (UInt16)dist; intDist[i] = uint16Dist; } // Bundle the results and Enqueue them sensorData dat = new sensorData(); dat.data = intDist; dat.TimeStamp = time; dat.timeIndex = j; lock (locker) dataQ.Enqueue(dat); wh.Set // Output results to file. sw2.Write(j.ToString() + ", "); foreach (UInt16 dd in dat.intData) { sw2.Write(dd.ToString() + ", "); } sw2.WriteLine(); // Increments time and index. j++; time += 1 / collectedData.signalFrequency; Thread.Sleep(2); } // Clean up sw2.Close(); lock (locker) dataQ.Enqueue(null); wh.Set(); sw2.Close(); } </code></pre> <p>Example line in the output file <strong>QueuedDataTest.txt</strong></p> <blockquote> <p>6, 4936, 9845, 24125, 44861,</p> </blockquote> <p><strong>Dequeue Data Method</strong></p> <p>This Method dequeues elements from the queue and writes them to a file. Until a null element is found on the queue at which point the job is done.</p> <pre><code> private void dequeueDataMethod() { StreamWriter sw = File.CreateText("C:\\tmp\\DequeueDataTest.txt"); while (true) { sensorData data = null; // Dequeue available element if any are there. lock (locker) if (dataQ.Count &gt; 0) { data = dataQ.Dequeue(); if (data == null) { sw.Close(); return; } } // Check to see if an element was dequeued. If it was write it to file. if (data != null) { sw.Write(data.timeIndex.ToString() + ", "); foreach (UInt16 dd in data.data) sw.Write(dd.ToString() + ", "); sw.WriteLine(); } else { wh.WaitOne(); } } </code></pre> <p>Output result after dequeueing the data and writing it to <strong>DequeueDataTest.txt</strong></p> <blockquote> <p>6, 64791, 19466, 47772, 65405,</p> </blockquote> <hr> <p><strong>Updates 1:</strong></p> <p><strong>Location of Locks in current code.</strong></p> <hr> <p>I have edited the code to place locks around the writing data to the file. So the code blocks I have locks around are as follows.</p> <p>In the <em>CalculateAndEnqueueData()</em> method I have</p> <pre><code>lock (locker) dataQ.Enqueue(dat); wh.Set lock(locker) { sw2.Write(j.ToString() + ", "); foreach (UInt16 dd in dat.intData) { sw2.Write(dd.ToString() + ", "); } sw2.WriteLine(); } </code></pre> <p>In the <em>dequeueDataMethod()</em> I have two areas with locks the first is here</p> <pre><code>lock(locker) if (dataQ.Count &gt; 0) { data = dataQ.Dequeue(); if (data == null) { sw.Close(); return; } } </code></pre> <p>which I assume locks locker for the code in the <em>if</em> block. The second is where I write the to the file here </p> <pre><code>lock (locker) { sw.Write(data.timeIndex.ToString() + ", "); foreach (UInt16 dd in data.intData) sw.Write(dd.ToString() + ", "); sw.WriteLine(); if (icnt &gt; 10) { sw.Close(); return; } this.label1.Text = dataQ.Count.ToString(); } </code></pre> <p>That's all of them.</p> <hr>
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    1. COSurely you could make the code way, way simpler and still demonstrate the problem you're seeing.
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      1. USJay Bazuzi
    2. COyou are locking the queue, but where is the synchronisation on your StreamWriter???
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      1. USMitch Wheat
    3. COEach thread writes to a separate file. So I didn't think I would need synchronization for that part of the thread. Am I wrong?
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