fix: Prevent deadlocks when mixing threads with queue based execution context

[WojciechMazur]

• Prevent deadlocks or pre-early exit when mixing threads with queue based execution context
• NativeThread.registry.aliveThreads now returns iterator instead of array
• Use thread-safe queue in QueueExecutionContext - there is always 1 consumer, but there can be multiple producers

Can help with resolving #3848 - the scaltest framework snapshot might have been adding new tasks to the queue.

[ekrich]

@WojciechMazur This is very nice. What is the purpose of naming a class package.state.scala? Not familiar with that convention / choice.

[WojciechMazur]

What is the purpose of naming a class package.state.scala? Not familiar with that convention / choice.

The main purpose here was to cleanup the access to the statefull data. We don't want to store any state in runtime directly - this way when calling any of the methods defined in it, we would not need to obtain the runtime object instance. Instead we define them in seperate objects. The problem is that it's defined as package object runtime. Becose of that we cannot restrict access of the state container to be private[runtime]. So we moved them to another file that is defined in package scala.scalanative.runtime.

If the state would not be referenced from outside the file then we could have just used private access modifer, but we want to send notification from other runtime entities - from NativeThread or QueueExecutionContext

The naming might be confusing, after all that might not be allowed in Java, so it's not familiar in the Scala. However, we already do something like that in scala-cli, where we can define tests using MyLogic.test.scala to place the test sources in the same directories as the main sources. There isn't anything blocking us from that, and it seemed to be the most clean solution as the state and the stateless source files are placed next to each other

[ekrich]

Thank you for the explanation. I hadn't seen that naming before and the info about package object and access control is good info too. Fine tuned design is an art and I am not really at that level.