What is the difference between synchronous and asynchronous requests?

Synchronous requests block the current thread until a response is received. Asynchronous requests do not block the thread; the response is handled upon completion of the operation, usually through a callback mechanism, delegate, or closure.

Characteristic	Synchronous request	Asynchronous request
Thread blocking	Yes	No
UI responsiveness	Can block the UI	Does not block the UI
Implementation complexity	Simpler	More complex (state management)
Usage in iOS	Rarely, only for short tasks, not on the main thread	Preferably, especially for long operations

Example of an asynchronous request using URLSession:

// Create a URLSessionTask
let task = URLSession.shared.dataTask(with: url) { data, response, error in
    // This block executes asynchronously after the request completes
    if let error = error {
        print("Error: \(error.localizedDescription)")
        return
    }

    // Handling received data
    if let data = data {
        print("Data received, bytes: \(data.count)")
    }

    // UI updates should happen on the main thread
    DispatchQueue.main.async {
        // Update UI
    }
}

// Start the task
task.resume()

// Code here executes immediately, without waiting for the request to finish
print("Request sent")