What are common reasons for deadlocks?

Question

Deadlocks are hard to find and very uncomfortable to remove.

How can I find error sources for deadlocks in my code? Are there any \"deadlock patterns\"?

In m

Answer 1

No deadlock patterns to my knowledge (and 12 years of writing heavily multithreaded trading applications).. But the TimedLock class has been of great help in finding deadlocks that exist in code without massive rework.

http://www.randomtree.org/eric/techblog/archives/2004/10/multithreading_is_hard.html

basically, (in dotnet/c#) you search/replace all your "lock(xxx)" statements with "using TimedLock.Lock(xxx)"

If a deadlock is ever detected (lock unable to be obtained within the specified timeout, defaults to 10 seconds), then an exception is thrown. My local version also immediately logs the stacktrace. Walk up the stacktrace (preferably debug build with line numbers) and you'll immediately see what locks were held at the point of failure, and which one it was attempting to get.

In dotnet 1.1, in a deadlock situation as described, as luck would have it all the threads which were locked would throw the exception at the same time. So you'd get 2+ stacktraces, and all the information necessary to fix the problem. (2.0+ may have changed the threading model internally enough to not be this lucky, I'm not sure)