Using the same lock for multiple methods

Question

I haven\'t had any issues using the same lock for multiple methods so far, but I\'m wondering if the following code might actually have issues (performance?) that I\'m not a

Answer 1

Good question. There are pros and cons of making locks more fine grained vs more coarse grained, with one extreme being a separate lock for each piece of data and the other extreme being one lock for the entire program. As other posts point out, the disadvantage of reusing the same locks is in general you may get less concurrency (though it depends on the case, you may not get less concurrency).

However, the disadvantage of using more locks is in general you make deadlock more likely. There are more ways to get deadlocks the more locks you have involved. For example, acquiring two locks at the same time in separate threads but in the opposite order is a potential deadlock which wouldn't happen if only one lock were involved. Of course sometimes you may fix a deadlock by breaking one lock into two, but usually fewer locks means fewer deadlocks. There's also added code complexity of having more locks.

In general these two factors need to be balanced. It's common to use one lock per class for convenience if it doesn't cause any concurrency issues. In fact, doing so is a design pattern called a monitor.

I would say the best practice is to favor fewer locks for code simplicity's sake and make additional locks if there's a good reason (such as concurrency, or a case where it's more simple or fixes a deadlock).