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POMultithreaded Synchronised List<T>
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  1. POMultithreaded Synchronised List<T>
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    copied!<p>I have a requirement whereby I needed to store a simple cache of a list of items. I was using List&lt; T > for this purpose, but we have now changed the design to accommodate multiple threads.</p> <p>The architecture of the system is driven by events, therefore it's quite likely that a read and write operation could collide. Since the vast majority of access will be read-only I thought that the ReaderWriterLockSlim might be a good candidate. The cache only needs to be accurate at the point of reading for that moment in time.</p> <p>I have written the code below and it seems to work ok, but are there some potential pain points?</p> <p><strong>UPDATE: Whilst the code below does fix some synchronisation problems it's not 100% perfect. I have since decided to implement a much simpler class that doesn't expose all of the IList&lt; T > operations and therefore makes it 'safer' to re-use.</strong></p> <pre><code>public class SynchronisedList&lt;T&gt; : IList&lt;T&gt; { private ReaderWriterLockSlim cacheLock = new ReaderWriterLockSlim(); private IList&lt;T&gt; innerCache = new List&lt;T&gt;(); private U ReadReturn&lt;U&gt;(Func&lt;U&gt; function) { cacheLock.EnterReadLock(); try { return function(); } finally { cacheLock.ExitReadLock(); } } private void Read(Action action) { cacheLock.EnterReadLock(); try { action(); } finally { cacheLock.ExitReadLock(); } } private U WriteReturn&lt;U&gt;(Func&lt;U&gt; function) { cacheLock.EnterWriteLock(); try { return function(); } finally { cacheLock.ExitWriteLock(); } } private void Write(Action action) { cacheLock.EnterWriteLock(); try { action(); } finally { cacheLock.ExitWriteLock(); } } public T this[int index] { get { return ReadReturn(() =&gt; innerCache[index]); } set { Write(() =&gt; innerCache[index] = value); } } public int IndexOf(T item) { return ReadReturn(() =&gt; innerCache.IndexOf(item)); } public void Insert(int index, T item) { Write(() =&gt; innerCache.Insert(index, item)); } public void RemoveAt(int index) { Write(() =&gt; innerCache.RemoveAt(index)); } public void Add(T item) { Write(() =&gt; innerCache.Add(item)); } public void Clear() { Write(() =&gt; innerCache.Clear()); } public bool Contains(T item) { return ReadReturn(() =&gt; innerCache.Contains(item)); } public int Count { get { return ReadReturn(() =&gt; innerCache.Count); } } public bool IsReadOnly { get { return ReadReturn(() =&gt; innerCache.IsReadOnly); } } public void CopyTo(T[] array, int arrayIndex) { Read(() =&gt; innerCache.CopyTo(array, arrayIndex)); } public bool Remove(T item) { return WriteReturn(() =&gt; innerCache.Remove(item)); } public IEnumerator&lt;T&gt; GetEnumerator() { return ReadReturn(() =&gt; innerCache.GetEnumerator()); } IEnumerator IEnumerable.GetEnumerator() { return ReadReturn(() =&gt; (innerCache as IEnumerable).GetEnumerator()); } } internal class Program { private static SynchronisedList&lt;int&gt; list = new SynchronisedList&lt;int&gt;(); private static void Main() { for (int i = 0; i &lt; 500000; i++) { var index = i; ThreadPool.QueueUserWorkItem((state) =&gt; { var threadNum = (int)state; if (threadNum % 10 == 0) { list.Add(threadNum); } else { Console.WriteLine(list.Count); } }, index); } Console.ReadKey(); } } </code></pre>
 

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