How to deal with application termination/teardown/deinit with Swift Concurrency?

Using Swift
1

My Cocoa application wants to disconnect a network client before quitting. Seems pretty straightforward, but the operation is async throws.

So far, I have this to handle termination:

  @MainActor func applicationWillTerminate(_: Notification) {
    Task {
      try! await viewController.tearDownClient()
    }
  }

This doesn't actually work because the Task gets scheduled to run later. The application is currently about to terminate, so there is no "later" for the Task to run in.

I have run into a similar situation with the actual view controller itself:

  deinit {
    Task {
      try! await tearDownClient()
    }
  }

This doesn't work for similar reasons.

I suppose what I need is a way to block on the completion of these asynchronous operations. I realize that is an undesired operation most of the time, but I don't see another way.

2 Likes
2

Assuming we're talking about NSApplicationDelegate, then use applicationShouldTerminate(_:) to control the behavior.

1 Like
3

Thank you, I didn't know about this! Just patched my app to advantage of this and now all's well—clients terminate when quitting the app.

I am still curious about tearing down the network client in deinit, although that is less important to me.

4

Thinking about it, though, deinit seems fundamentally incompatible with concurrency. deinit should really be a one-shot, synchronous operation, and wanting to kick off an operation that could possibly involve switching between tasks in a thread pool feels analogous to wanting to fit a square peg into a round hole.

1 Like