A very simple way of avoiding deadlock (circular dependencies) is to grab locks in a fixed order (if you want to get the N+1th lock then you have to acquire all of them from 1 to N. This way you avoid the situation where thread 1 has already acquired lock X, thread 2 has acquired Y, then thread 2 wants to acquire X and thread 1 wants Y.
The problem is that this strategy is only applicable in a very-very limited context, in most cases it's useless because the number of lockable resources changes dynamically and/or it's not feasible/scalable to get all locks up to N+1.
The problem is that this strategy is only applicable in a very-very limited context, in most cases it's useless because the number of lockable resources changes dynamically and/or it's not feasible/scalable to get all locks up to N+1.