How can DispatchGroup be used to sequentially execute requests with the ability to cancel on the third without waiting for the fourth?

DispatchGroup in iOS is typically used to track the completion of multiple asynchronous tasks. However, for sequential execution of requests with the ability to interrupt at the third request without waiting for the fourth, the following approach can be used:

1. Do not start all requests simultaneously, but start them sequentially, waiting for the previous one to complete.
2. Use DispatchGroup for each request to track its completion.
3. When an interrupt condition occurs (e.g., an error on the third request), do not start the next request and exit the chain.

Example in Swift:

let dispatchGroup = DispatchGroup()

func performRequestsSequentially() {
    dispatchGroup.enter()
    performRequest1 { success in
        dispatchGroup.leave()
        guard success else { return }

        dispatchGroup.enter()
        performRequest2 { success in
            dispatchGroup.leave()
            guard success else { return }

            dispatchGroup.enter()
            performRequest3 { success in
                dispatchGroup.leave()
                guard success else { return }

                // If needed, you can start the fourth request
                // performRequest4 { ... }
            }
        }
    }
}

func performRequest1(completion: @escaping (Bool) -> Void) {
    // Asynchronous request
    completion(true) // or false in case of error
}

func performRequest2(completion: @escaping (Bool) -> Void) {
    completion(true)
}

func performRequest3(completion: @escaping (Bool) -> Void) {
    completion(false) // example of interruption
}

Thus, if the third request ends with an error (false), the fourth request will not be started. DispatchGroup helps track the completion of each request, but the sequence is controlled by nested calls.