Locking strategies and techniques for preventing deadlocks in code

Question

The common solution to preventing deadlock in code is to make sure the sequence of locking occur in a common manner regardless of which thread is accessing the resources.

Answer 1

Consistent ordering of locking is pretty much the first and last word when it comes to deadlock avoidance.

There are related techniques, such as lockless programming (where no thread ever waits on a lock, and thus there is no possibility of a cycle), but that's really just a special case of the "avoid inconsistent locking order" rule -- i.e. they avoid inconsistent locking by avoiding all locking. Unfortunately, lockless programming has its own issues, so it's not a panacea either.

If you want to broaden the scope a bit, there are methods for detecting deadlocks when they do occur (if for some reason you can't design your program to avoid them), and ways for breaking deadlocks when they do occur (e.g. by always locking with a timeout, or by forcing one of the deadlocked threads to have their Lock() command fail, or even just by killing one of the deadlocked threads); but I think they are all pretty inferior to simply making sure deadlocks cannot happen in the first place.

(btw if you want an automated way to check whether your program has potential deadlocks in it, check out valgrind's helgrind tool. It will monitor your code's locking patterns and notify you of any inconsistencies -- very useful)