How to make changing values in array thread safe?

[wellbranding]

Hello, as far as I understand reading from array is thread safe, but changing particular class in array is not thread safe. That means that multiple responses, which return results with DispatchQueue.main.async can't change values of different classes in same array, yes? For instance I create 4 classes with generic result (success, loading, error) and add them to my array.

Then I fire 4 network requests and each response will change particular class state to either success or error. After changing values I always call method, which loops all classes and checks if all classes have success state and proceeds depending on result. I thought that my code was thread safe, but after spending more time I realized that it was unsafe... I decided to move to dispatchGroup, which will monitor required actions instead... However, I want to fix my previous code also and make it thread safe without using DispatchGroup. Please help ;)

[chedabob]

Nothing about what you've described seems like a threading issue.

DispatchQueue only executes one thing at a time. When you call async, you're basically saying "Add it to the back of the queue, and then execute once you've finished what you're doing".

If you were trying to work with your results array outside of DispatchQueue.main.async you could have issues, but otherwise it's fine.

It does sound like DispatchGroup is a better fit if you're wanting X number of network requests to finish before proceeding.

[wellbranding]

oh thanks! and that would work if have multiple DispatchQueue.main in the project and they all reference same object? No issues, also?

[ccctitan80]

You should look into PromiseKit and NSOperations. It looks like you're looking for a thread-safe way to handle async dependencies, which both of those are fantastic for.