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POWhen is ReaderWriterLockSlim better than a simple lock?
 

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  1. POWhen is ReaderWriterLockSlim better than a simple lock?
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    <p>I'm doing a very silly benchmark on the ReaderWriterLock with this code, where reading happens 4x more often than writting:</p> <pre><code>class Program { static void Main() { ISynchro[] test = { new Locked(), new RWLocked() }; Stopwatch sw = new Stopwatch(); foreach ( var isynchro in test ) { sw.Reset(); sw.Start(); Thread w1 = new Thread( new ParameterizedThreadStart( WriteThread ) ); w1.Start( isynchro ); Thread w2 = new Thread( new ParameterizedThreadStart( WriteThread ) ); w2.Start( isynchro ); Thread r1 = new Thread( new ParameterizedThreadStart( ReadThread ) ); r1.Start( isynchro ); Thread r2 = new Thread( new ParameterizedThreadStart( ReadThread ) ); r2.Start( isynchro ); w1.Join(); w2.Join(); r1.Join(); r2.Join(); sw.Stop(); Console.WriteLine( isynchro.ToString() + ": " + sw.ElapsedMilliseconds.ToString() + "ms." ); } Console.WriteLine( "End" ); Console.ReadKey( true ); } static void ReadThread(Object o) { ISynchro synchro = (ISynchro)o; for ( int i = 0; i &lt; 500; i++ ) { Int32? value = synchro.Get( i ); Thread.Sleep( 50 ); } } static void WriteThread( Object o ) { ISynchro synchro = (ISynchro)o; for ( int i = 0; i &lt; 125; i++ ) { synchro.Add( i ); Thread.Sleep( 200 ); } } } interface ISynchro { void Add( Int32 value ); Int32? Get( Int32 index ); } class Locked:List&lt;Int32&gt;, ISynchro { readonly Object locker = new object(); #region ISynchro Members public new void Add( int value ) { lock ( locker ) base.Add( value ); } public int? Get( int index ) { lock ( locker ) { if ( this.Count &lt;= index ) return null; return this[ index ]; } } #endregion public override string ToString() { return "Locked"; } } class RWLocked : List&lt;Int32&gt;, ISynchro { ReaderWriterLockSlim locker = new ReaderWriterLockSlim(); #region ISynchro Members public new void Add( int value ) { try { locker.EnterWriteLock(); base.Add( value ); } finally { locker.ExitWriteLock(); } } public int? Get( int index ) { try { locker.EnterReadLock(); if ( this.Count &lt;= index ) return null; return this[ index ]; } finally { locker.ExitReadLock(); } } #endregion public override string ToString() { return "RW Locked"; } } </code></pre> <p>But I get that both perform in more or less the same way:</p> <pre><code>Locked: 25003ms. RW Locked: 25002ms. End </code></pre> <p>Even making the read 20 times more often that writes, the performance is still (almost) the same. </p> <p>Am I doing something wrong here?</p> <p>Kind regards.</p>
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    1. CObtw, if I take out the sleeps: "Locked: 89ms. RW Locked: 32ms. " - or bumping up the numbers: "Locked: 1871ms. RW Locked: 2506ms.".
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    2. COIf i remove the sleeps, locked is faster than rwlocked
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    3. COIt's because the code you're synchronizing is too fast to create any contention. See Hans's answer, and my edit.
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      1. USDan Tao
 

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