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POCannot find bug in C# 4.0 Parallel.For loop using thread-specific variables
 

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  1. POCannot find bug in C# 4.0 Parallel.For loop using thread-specific variables
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    <p>I am attempting to model slot machine behavior with parallel programming, using a base class (SlotBase) which will be overridden by classes representing each individual machine.</p> <p>In the base class, I have a method that (attempts to) invoke a descendant class's method (marked abstract in the base class) that plays a sample and returns results through use of output parameters, and then using a mutually exclusive lock, updates the base class's summation variables.</p> <p>Relevant code samples as follows: <em>From SlotBase.cs:</em></p> <pre><code>#region Member Variables protected long m_CoinIn; protected long[] m_CoinOut; protected string[] m_FeatureList; protected long[] m_HitCount; // .. and many more, but redacted for length #endregion protected abstract void PlaySample(long sampleSize, out long coinIn, out long[] coinOut, out long[] hitCount); protected override void DoSimulation() { // No need to intialize these, as the calling routine will, and only it knows how big the arrays need to be, and so forth. object mutex = new object(); if (ParallelMode) { int periodCount = (int)(BatchSize / PeriodSize); Parallel.For(0, periodCount, delegate(int i) { long coinIn; long[] coinOut; long[] hitCount; PlaySample(PeriodSize, out coinIn, out coinOut, out hitCount); lock (mutex) { Console.WriteLine("Coin in this batch: {0}", coinIn); m_CoinIn += coinIn; for (int j = 0; j &lt; m_FeatureList.Length; ++j) { m_CoinOut[j] += coinOut[j]; m_HitCount[j] += hitCount[j]; } } }); } } </code></pre> <p>.. and from a typical subclass implementation:</p> <pre><code>protected override void PlaySample(long sampleSize, out long coinIn, out long[] coinOut, out long[] hitCount) { switch (WagerIndex) { case (int)WagerType.Main: { RNG localRNG = SpawnRNG(); coinIn = 0; coinOut = new long[m_FeatureList.Length]; hitCount = new long[m_FeatureList.Length]; for (long iter = 0; iter &lt; sampleSize; ++iter) { coinIn += m_LinesPlayed; double[] output = GetSpinResults(ref localRNG, (int)SpinMode.MainSpin); for (int i = 0; i &lt; m_FeatureList.Length; ++i) { coinOut[i] += (long)output[i]; if (output[i] &gt; 0) ++hitCount[i]; } } break; } default: { throw new Exception(string.Format("Wager Type index {0} not supported", WagerIndex)); } } } </code></pre> <p>.. this actually works quite effectively with small values of <em>SampleSize</em> and <em>PeriodSize</em> but quickly proceeds to hang (or virtually hang) as values increase.</p> <p>I've tried commenting out the variable updates and the hanging continues in earnest, which suggests that the problem is in fact with the way I'm implementing the <em>Parallel.For</em> loop.</p> <p>I have no problems tearing this down pretty much from scratch and rebuilding to get this working. My only really important design goal in that I have the same paradigm (one base class, multiple sub-classes for implementation of different slots).</p> <p>Where am I going wrong?</p>
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    1. PTQuestion
    1. USdavenewza
    1. USCharles
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    1. COThis [question](http://stackoverflow.com/questions/6977218/parallel-foreach-can-cause-a-out-of-memory-exception-if-working-with-a-enumera/6977656#6977656) may help - I can't tell if your process is CPU bound from the code above, because it isn't obvious what `SpawnRNG` and `GetSpinResults` are doing. I would play with `ParallelOptions.MaximumDegreeOfParallelism` and see what happens.
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      1. POCannot find bug in C# 4.0 Parallel.For loop using thread-specific variables
      1. USdavisoa
    2. CO**small values** _small_ is very relative. What are the numbers we talk about? And do you care about the hangs or the performance itself?
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      1. POCannot find bug in C# 4.0 Parallel.For loop using thread-specific variables
      1. USigrimpe
    3. COI care about the hangs and the performance because the values are small relative to the amount of iterations I need to run. To give exact values, this runs five with PeriodSize = 1000 and BatchSize = 100000; change that to 2k/200k and it starts to lag a bit near the end of the runs; 4k/400k and it hangs permanently.
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      1. USCharles
 

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