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POInterlocked.Read / Interlocked.Exchange much slower on Mono than .NET?
 

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  1. POInterlocked.Read / Interlocked.Exchange much slower on Mono than .NET?
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    <p><strong>Sorry for the long question, but there's a Jon Skeet reference, so it may be worthwhile for some.</strong></p> <p><strong>In short:</strong><br /> <code>Interlocked.Read</code> / <code>Interlocked.Exchange</code> seem to perform much slower while running in the Mono framework than while running in the .NET framework. I'm curious to know why.</p> <p><strong>In long:</strong><br /> I wanted a thread-safe double for 32-bit platforms, so I made this struct:</p> <pre><code>public interface IThreadSafeDouble { double Value { get; set; } } public struct LockedThreadSafeDouble : IThreadSafeDouble { private readonly object Locker; private double _Value; public double Value { get { lock (Locker) return _Value; } set { lock (Locker) _Value = value; } } public LockedThreadSafeDouble(object init) : this() { Locker = new object(); } } </code></pre> <p>Then I read Jon Skeet's answer to <a href="https://stackoverflow.com/questions/531759/c-sharp-volatile-double">this question</a>, so I made this struct:</p> <pre><code>public struct InterlockedThreadSafeDouble : IThreadSafeDouble { private long _Value; public double Value { get { return BitConverter.Int64BitsToDouble(Interlocked.Read(ref _Value)); } set { Interlocked.Exchange(ref _Value, BitConverter.DoubleToInt64Bits(value)); } } } </code></pre> <p>Then I wrote this test:</p> <pre><code> private static TimeSpan ThreadSafeDoubleTest2(IThreadSafeDouble dbl) { var incrementTarg = 10000000; var sw = new Stopwatch(); sw.Start(); for (var i = 0; i &lt; incrementTarg; i++, dbl.Value++); sw.Stop(); return sw.Elapsed; } private static void ThreadSafeTest() { var interlockedDbl = new InterlockedThreadSafeDouble(); var interlockedTim = ThreadSafeDoubleTest2(interlockedDbl); var lockedDbl = new LockedThreadSafeDouble(true); var lockedTim = ThreadSafeDoubleTest2(lockedDbl); System.Console.WriteLine("Interlocked Time: " + interlockedTim); System.Console.WriteLine("Locked Time: " + lockedTim); } public static void Main(string[] args) { for (var i = 0; i &lt; 5; i++) { System.Console.WriteLine("Test #" + (i + 1)); ThreadSafeTest(); } System.Console.WriteLine("Done testing."); System.Console.ReadLine(); } </code></pre> <p>And I got this result using the .NET framework: <img src="https://i.stack.imgur.com/QFvz9.jpg" alt=".NET Interlocked test results"></p> <p>And this result using the Mono framework: <img src="https://i.stack.imgur.com/Qme8Q.jpg" alt="Mono Interlocked test results"></p> <p>I've ran both tests multiple times on the same machine (Windows XP) and the results are consistent. I'm curious to know why Interlocked.Read/Interlocked.Exchange seems to perform so much slower on the Mono framework.</p> <p><strong>Update:</strong></p> <p>I wrote the following, simpler test:</p> <pre><code>long val = 1; var sw = new Stopwatch(); sw.Start(); for (var i = 0; i &lt; 100000000; i++) { Interlocked.Exchange(ref val, 2); // Interlocked.Read(ref val); } sw.Stop(); System.Console.WriteLine("Time: " + sw.Elapsed); </code></pre> <p>The .NET framework consistently returns <strong>~2.5</strong> seconds with both <code>Exchange</code> and <code>Read</code>. The Mono framework returns <strong>~5.1</strong> seconds.</p>
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    1. COI'd start with "this test is not really useful": run .Net 4.0 64bit on Windows and Mono on Linux to compare how current versions perform.
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      1. USskolima
    2. COYou don't actually know if it's the Interlocked methods that's slower, it might also be the interface dispatch. I suggest stripping out as much generalization as possible before drawing any conclusions (i.e. just put the Interlocked methods inside a loop).
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      1. POInterlocked.Read / Interlocked.Exchange much slower on Mono than .NET?
      1. USRolf Bjarne Kvinge
    3. CO@RolfBjarneKvinge -- I updated my question with a simpler test and the results.
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