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PO.NET Framework: Are objects apartment bound?
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copied!<p><strong>Given:</strong> Constructing an ADO Connection object from one thread and giving it to another thread is <strong><em>forbidden</em></strong>. The two threads are different apartments, and even though the first thread will <strong>never</strong> touch it again (not even maintain a reference to it!), it doesn't matter. </p> <p>That ADO Connection object was created by ThreadA, ThreadA is the only thread, ever, under any circumstances, at all, ever, that is allowed to use that Connection object, ever.</p> <p>Now replace "ADO Connection" with "ADO.NET Connection". Does the same rule apply?</p> <hr> <p>i know that most objects in the .NET framework are not thread-safe. For example, the <a href="http://msdn.microsoft.com/en-us/library/system.collections.dictionaryentry.aspx" rel="nofollow noreferrer">DictionaryEntry</a> structure in the SDK says: </p> <blockquote> <p><strong>Thread Safety</strong><br> Any public <strong>static</strong> members of this type are thread safe. Any instance members are not guaranteed to be thread safe.</p> </blockquote> <p>i understand that <strong>not thread-safe</strong> means that i have to synchronize access to the object if i am going to access it from different threads. That's all well and good, and i could ensure only one thread access the object at a time:</p> <pre><code>lock (myObject) { ... } </code></pre> <p>But there's something more than not being thread-safe. </p> <p>In COM, (some) objects are bound to the "<em>apartment</em>" that created it. Once the object has been constructed on one apartment, you are <strong><em>forbidden</em></strong> from accessing it from another apartment - no matter how much you protect that object from multiple simultaneous thread access.</p> <p>Does a similar concept exist in .NET? </p> <hr> <h2>More Information</h2> <p>i know you are forbidden from accessing Controls from threads other than the one that created it - even if you use it in a thread-safe manner. This is not documented on MSDN:</p> <blockquote> <p><strong>Thread Safety</strong></p> <p>Only the following members are thread safe: BeginInvoke, EndInvoke, Invoke, InvokeRequired, and CreateGraphics if the handle for the control has already been created. Calling CreateGraphics before the control's handle has been created on a background thread can cause illegal cross thread calls.</p> </blockquote> <p>There is no mention of Controls throwing exceptions when you create and use them from a single thread - when that thread is not the first thread that was created when the application started.</p> <p>But what about arbitrary objects? What about:</p> <pre><code>public class MyClass { int _number; public int Number { get { return _number; } set { _number = value; } } } MyClass myObject = new MyClass(); </code></pre> <p>As long as i synchronize access to myObject two threads are allowed to talk to it?</p> <hr> <p>The same goes for:</p> <pre><code>List<Object> sharedList = new List<Object>(); </code></pre> <p>Two threads can talk to the list, as long as they don't do it simultaneously, usually with:</p> <pre><code>lock (sharedList) { sharedList.Add(data); } </code></pre> <p>are two threads allowed to touch the same object?</p> <hr> <p>The same goes for:</p> <pre><code>IAsyncResult ar = BeginSetLabelToTheValueINeed(label1); ... EndSetLabelToTheValueINeed(ar); </code></pre> <hr> <p>The same goes for:</p> <pre><code>//Fetch image on connection that is an existing DB transaction public static Bitmap GetImageThumbnail(DbConnection conn, int imageID) { } </code></pre> <p>being converted into the asynchronous delegate pattern:</p> <pre><code>//Begin fetching an image on connection that is an existing DB transaction IAsyncResult ar = BeginGetImageThumbnuts(conn, imageID, callback, stateOjbect); ... //Finish fetching an image on connection that is an existing DB transaction Bitmap thumb = EndGetImageNumbthail(ar); </code></pre> <hr> <p>Rather than answering the question, people went off on a discussion about design patterns in ADO.NET. Please answer the question. Ignore the examples if they confuse and distract your squirrel brains.</p>

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