Occasional EXC_BAD_ACCESS crash

Every now and then, my app crashes with a EXC_BAD_ACCESS when accessing a Dictionary, although the object exists and has been accessed many times before the crash without any problem.

It is created at start of app with:

static var whiteLabelling = [String : String]()

and is never recreated afterwards.

Entries may be added, changed and removed at runtime, and, depending on the situation, it can run through a FareEngine.whiteLabelling.removeAll()

Multiple threads access it simultaneously as well without crashing.

What can be the reason for this occasional crash?

You should ensure that you always read from the same thread.

You could use always main thread with a basic DispatchQueue.main.async{}. That way, it's always in the same queue (main thread/thread 0).

Another possible way would be using a private queue, ensuring it's always in that same queue.

• add a (private) property to FareEngine

static private var whiteLabellingQueue = DispatchQueue(label: "com.yourApp.whiteLabellingQueue, qos: .userInitiated) //or any other `qos`

• Make whiteLabelling private (to ensure there is no more issue with other code accessing it):

private static var whiteLabelling: [String: String]

• Then, make access possible:

func setWhiteLabelling(value: String, forKey key: String) {
    whiteLabellingQueue.sync {
        self.whiteLabelling[key] = value
    }
}

• Finally, make writing possible:

func getWhiteLabelling(forKey key: String) -> String? {
    let value: String?
    whiteLabellingQueue.sync {
        value = self.whiteLabelling[key]
    }
    return value
}

Now, when you want to access the values:

let req = FareEngine.getWhiteLabelling(forKey: "GPSACCURACY")

Since, you can have a remove all, do the same:

func cleanWhiteLabelling() {
    whiteLabellingQueue.sync {
        self.whiteLabelling.removeAll()
    }
}