Close/Dispose on FileStream

Question

I've got a bit of code in a product I am supporting that copies files:

using(System.IO.FileStream sourceFS = new System.IO.FileStream(sourcePath, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read))
            {
                using(System.IO.FileStream targetFS = new System.IO.FileStream(targetPath, System.IO.FileMode.Create, System.IO.FileAccess.Write, System.IO.FileShare.Read))
                {
                    while((read = sourceFS.Read(buffer, 0, buffer.Length)) > 0)
                    {
                        targetFS.Write(buffer, 0, read);
                    }

                    targetFS.Flush();
                    targetFS.Close();
                }

                sourceFS.Close();
            }

Unfortunately, the users are reporting an exception informing us that the destination file is in use by another process. I've asked if there is a chance that someone has the file open (it's an Excel file) - apparently not...

So, I put the thinking cap on... Is it possible we are leaving the destination file with a file lock against it? The only way I can see for targetFS not to be closed would be require both:

1. An exception to be thrown within the inner using block, and
2. The Dispose method not to actually close the stream.

This sounded unlikely to me, but ever curious I used dotPeek from JetBrains to disassemble the Dispose method on the FileStream class - which doesn't seem to do all that much really - I'm guessing its "close" behaviour is provided by disposing of the handle...

In essence though - the question is this - can anyone spot how this might be leaving a file with a lock against it?

Answer 1

Look elsewhere. This code is fine. Not sure what else to say about it. using is meant for exactly this use case - failsafe disposal.

Investigate using Process Explorer which process is holding a handle to the file in question.