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I've just finished reading "C# 4.0 in a Nutshell" (O'Reilly) and I think it's a great book for a programmer willing to switch to C#, but it left me wondering. My problem is the definition of using statement. According to the book (p. 138), using (StreamReader reader = File.OpenText("file.txt")) { ... } is precisely equivalent to: StreamReader reader = File.OpenText("file.txt"); try { ... } finally { if (reader != null) ((IDisposable)reader).Dispose(); } Suppose, however, that this is true and that this code is executed in a separate thread. This thread is now aborted with thread.Abort() , so a ThreadAbortException is thrown and suppose the thread is exactly after initializing the reader and before entering the try..finally clause. This would mean that the reader is not disposed! A possible solution would be to code this way: StreamReader reader = null; try { reader = File.OpenText("file.txt"); ... } finally { if (reader != null) ((IDisposable)reader).Dispose(); } This would be abort-safe. Now for my questions: Are authors of the book right and the using statement is not abort-safe or are they wrong and it behaves like in my second solution? If using is equivalent to the first variant (not abort-safe), why does it check for null in finally ? According to the book (p. 856), ThreadAbortException can be thrown anywhere in managed code. But maybe there are exceptions and the first variant is abort-safe after all? EDIT: I know that using thread.Abort() is not considered good practice. My interest is purely theoretical: how does the using statement behave exactly ?

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