Visualize swift concurrency

Use the new instruments tool to see timelines for tasks, threads, actors, etc. Task creation call stacks.

• Common problems
  • Main actor blocking
    • Don’t do extra stuff on the main thread
  • Actor contention
    • Be aware of doing large amounts of work on a single actor. Tasks can then not run in parallel.
    • Only run on the actor only when they need exclusive access to actors data, with nonisolated chunks of the code.
  • Thread pool exhaustion
    • Don’t call blocking calls that wait without suspending.
    • File/networks need to use concurrent versions.
    • This can lead to running out of queues, slowing down, and even deadlocking.
    • If you need to use this stuff, do it outside of concurrency land, with dispatches and continuations.
  • Continuation misuse
    • Always call the callback, exactly once.
    • If called twice, program will crash.
    • If not called, task will leak and never resume.
    • Always use checked continuation, which detects misuse