Hi, Is the `IO.unsafeRunSync()` so dangerous that it cannot be called in production code? I need to...

# arrow

[dnowak]

Hi, Is the IO.unsafeRunSync() so dangerous that it cannot be called in production code? I need to execute IO in the current thread and unsafeRunSync seems reasonable in such case. Questions:
1. What can go wrong during the execution of unsafeRunSync?
2. How to execute IO in the current thread?

[pakoito]

2 is not visible as an scheduler yet https://kotlinlang.slack.com/archives/C5UPMM0A0/p1586437549202900

1 .attempt().unsafeRunSync() runs your program as returns an Either. It’s meant as an entry point. If you need to do IO inside something that’s not entry-programmy like an event callback, there’s a way of doing it through a Promise or a Channel.

[pakoito]

Promise/Queue still require calling unsafeRunAsync to set a value. Still, they decouple your business logic from the event handler, and makes it easier to test.

[pakoito]

instead of

system.handleEvent {
  val bla = run(it).unsafeRunSync() // block thread
  continue(bla) // side-effect outside IO
}

you have

IO.fx {
  continueOn(dispatchers().default()) // process on the background
  val next = queue.take().bind()
  val bla = run(it).bind()
  effect { continue(bla) }.bind()
}.unsafeRunAsync { } // immediately free the thread

system.handleEvent {
 queue.offer(it)
  .fork() // offer the value on the background
  .unsafeRunAsync { } // immediately free the thread
}

[pakoito]

if instead of that you are at a place that supports suspension, then myIO.attempt().suspended() is better than unsafeRunAsync()