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POIs this how to write a Thread-Safe IComparable?
 

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  1. POIs this how to write a Thread-Safe IComparable?
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    <p>I have a simple class and I want to make it thread-safe. The class needs to implement IComparer. I know that implementing the <code>int CompareTo(T other)</code> in a thread-safe way is not straight-forward. It's easy to allow a deadlock if I don't lock in the right way. I have three questions:</p> <ol> <li>Is this code thread-safe? If not, how can I fix it?</li> <li>Can this code be any shorter? It seems like a lot of code for a simple subtraction.</li> <li>Should I even bother making <code>int CompareTo(T other)</code> thread-safe? Should I instead require that the caller (usually sorting) lock all of the relevant BObjects?</li> </ol> <p>Here's my code:</p> <pre><code>public class BObject : IComparable&lt;BObject&gt; { //Each BObject has a unique object id private static int _bObjectId = 0; private static int GetNextId() { return System.Threading.Interlocked.Increment(ref BObject._bObjectId); } private object _locker = new object(); private readonly int _id = BObject.GetNextId(); //Some variable private int _sales; public int Sales { get { lock (this._locker) return this._sales; } set { lock (this._locker) this._sales = value; } } public int CompareTo(BObject other) { int result; //Can I simply do "if (this._id == other._id)" if (object.ReferenceEquals(this, other)) result = 0; else { //get the BObject with the lower id BObject lower = this._id &lt; other._id ? this : other; //get the BObject with the higher id BObject higher = this._id &gt; other._id ? this : other; //lock the BObject with the lower id first lock (lower._locker) { //lock the BObject with the higher id last lock (higher._locker) { //put object with lower Sales first result = this.Sales - other.Sales; } } } return result; } } </code></pre>
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    1. USuser2023861
    1. USuser2023861
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      1. POIs this how to write a Thread-Safe IComparable?
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    1. COLocking every member does not make your code thread-safe.
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      1. POIs this how to write a Thread-Safe IComparable?
      1. USSLaks
    2. COIn particular, `int`s are already atomic; you don't need locks at all.
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      1. POIs this how to write a Thread-Safe IComparable?
      1. USSLaks
    3. COSimplest way to make the comparison thread-safe: make your type immutable.
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      1. POIs this how to write a Thread-Safe IComparable?
      1. USJon Skeet
 

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