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    <p>From the C# language reference <a href="http://msdn.microsoft.com/en-us/library/c5kehkcz.aspx" rel="noreferrer">here</a>:</p> <blockquote> <p>In general, avoid locking on a public type, or instances beyond your code's control. The common constructs <code>lock (this)</code>, <code>lock (typeof (MyType))</code>, and <code>lock ("myLock")</code> violate this guideline:</p> <p><code>lock (this)</code> is a problem if the instance can be accessed publicly.</p> <p><code>lock (typeof (MyType))</code> is a problem if <code>MyType</code> is publicly accessible.</p> <p><code>lock("myLock")</code> is a problem because any other code in the process using the same string, will share the same lock. </p> <p>Best practice is to define a private object to lock on, or a private static object variable to protect data common to all instances.</p> </blockquote> <p>In your case, I would read the above guidance as suggesting that locking on the collection you will be modifying is bad practise. For example, if you wrote this code:</p> <pre><code>lock (otherProductList) { otherProductList = new List&lt;IProduct&gt;(); } </code></pre> <p>...then your lock will be worthless. For these reasons it's recommended to use a dedicated <code>object</code> variable for locking.</p> <p>Note that this doesn't mean your application will <em>break</em> if you use the code you posted. "Best practices" are usually defined to provide easily-repeated patterns that are more technically resilient. That is, if you follow best practice and have a dedicated "lock object," you are highly unlikely to <em>ever</em> write broken <code>lock</code>-based code; if you don't follow best practice then, maybe one time in a hundred, you'll get bitten by an easily-avoided problem.</p> <p>Additionally (and more generally), code written using best practices is typically more easily modified, because you can be less wary of unexpected side-effects.</p>
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    1. POWhy is it a bad practice to lock the object we are going to change?
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    1. USDan Puzey
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    1. COThat's a great answer, is there any other scenario, where this might cause an issue, please check i have updated the question
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    2. COok you're quoting MSDN, and repeating it is bad practice to lock publicly accessible objects, but still not telling *why* exactly this is a bad practice. E.g. the risk for deadlocks (answer of @ken2k) is another reason.
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    3. COWell, a particular example with the code you've posted would be that, although your variable is private, there's nothing to stop you passing that list to a method in another class. If that class were to `lock` on the list that you passed as a parameter (perhaps there is some other developer writing poor code in another component), it could affect the operation and/or performance of your code. This ties in with my final point: best-practise code is more easily modified, because the internal "locking object" would never be passed elsewhere.
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