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copied!<p>This could be a <em>massive</em> list - read Joe Duffy's excellent "<a href="http://rads.stackoverflow.com/amzn/click/032143482X" rel="noreferrer">Concurrent Programming On Windows</a>" for much more detail. This is pretty much a brain dump...</p> <ul> <li>Try to avoid calling into significant chunks of code while you own a lock</li> <li>Avoid locking on references which code outside the class might also lock on</li> <li>If you ever need to acquire more than one lock at a time, always acquire those locks in the same order</li> <li>Where reasonable, use immutable types - they can be shared freely between threads</li> <li>Other than immutable types, try to avoid the need to share data between threads</li> <li>Avoid trying to make your types threadsafe; most types don't need to be, and usually the code which needs to share data will need to control the locking itself</li> <li>In a WinForms app: <ul> <li>Don't perform any long-running or blocking operations on the UI thread</li> <li>Don't touch the UI from any thread other than the UI thread. (Use BackgroundWorker, Control.Invoke/BeginInvoke)</li> </ul></li> <li>Avoid thread-local variables (aka thread-statics) where possible - they can lead to unexpected behaviour, particularly on ASP.NET where a request may be served by different threads (search for "thread agility" and ASP.NET)</li> <li>Don't try to be clever. Lock-free concurrent code is <em>hugely</em> difficult to get right.</li> <li>Document the threading model (and thread safety) of your types</li> <li>Monitor.Wait should almost always be used in conjunction with some sort of check, in a while loop (i.e. while (I can't proceed) Monitor.Wait(monitor))</li> <li>Consider the difference between Monitor.Pulse and Monitor.PulseAll carefully every time you use one of them.</li> <li>Inserting Thread.Sleep to make a problem go away is never a real fix.</li> <li>Have a look at "Parallel Extensions" and the "Coordination and Concurrency Runtime" as ways of making concurrency simpler. Parallel Extensions is going to be part of .NET 4.0.</li> </ul> <p>In terms of debugging, I don't have very much advice. Using Thread.Sleep to boost the chances of seeing race conditions and deadlocks can work, but you've got to have quite a reasonable understanding of what's wrong before you know where to put it. Logging is very handy, but don't forget that the code goes into a sort of quantum state - observing it via logging is almost bound to change its behaviour!</p>

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