URLSessionDelegate class deinit not called - ios

Question

For client certificate authentication I've to use URLSessionDelegate in the custom class for handling all requests. The problem is the class is not deinitialize after a request made.
Code:
class Request: NSObject, URLSessionDelegate, URLSessionTaskDelegate{
func request(){
let url:URL = URL(string: "https://stackoverflow.com")!
let config = URLSessionConfiguration.default
URLSession(configuration: config, delegate: self, delegateQueue: .main).dataTask(with: url) { (data, response, error) in
print("Received")
}.resume()
}
func request2(){
let url:URL = URL(string: "https://stackoverflow.com")!
let config = URLSessionConfiguration.default
URLSession(configuration: config).dataTask(with: url) { (data, response, error) in
print("Received")
}.resume()
}
deinit {
print("Class deinit...")
}
}
When calling Request().request() then deinit is not called. Calling Request().request2() then deinit is called.
I am not sure how to resolve this problem. Please help me to find out the solution. Thank you...

Answer 1

URLSession keeps a strong reference to its delegate (self in your case). Check the official documentation:
The session object keeps a strong reference to the delegate until your app exits or explicitly invalidates the session. If you don’t invalidate the session, your app leaks memory until the app terminates.
You can invalidate the session using its methods finishTasksAndInvalidate() or invalidateAndCancel(). After that URLSession will release the strong reference to its delegate.
I guess you code example is just to demonstrate the behavior, but anyway I have to mention it's not a good practice to create a new URLSession for every single URLRequest.

Answer 2

In request() when assigning self to the delegate you are creating a strong reference to the instance of the class. This causes a retention cycle and stops the instance being deinitialised. The answer is to weekly capture the delegate:
URLSession(configuration: config, delegate: self, delegateQueue: .main).dataTask(with: url) { [weak self] (data, response, error) in
print("Received")
}.resume()
In request2() without a delegate this obviously isn't happening.
There are numerous blogs and tutorials about this, so rather than repeating them all I'll let you google for the detail about capture list and strong and weak references :-)