Implementing coroutines in Java

Question

This question is related to my question on existing coroutine implementations in Java. If, as I suspect, it turns out that there is no full implementation of coroutines cur

Answer 1

I just came across this question and just want to mention that i think it might be possible to implement coroutines or generators in a similar way C# does. That said i don't actually use Java but the CIL has quite similar limitations as the JVM has.

The yield statement in C# is a pure language feature and is not part of the CIL bytecode. The C# compiler just creates a hidden private class for each generator function. If you use the yield statement in a function it has to return an IEnumerator or an IEnumerable. The compiler "packs" your code into a statemachine-like class.

The C# compiler might use some "goto's" in the generated code to make the conversion into a statemachine easier. I don't know the capabilities of Java bytecode and if there's something like a plain unconditional jump, but at "assembly level" it's usually possible.

As already mentioned this feature has to be implemented in the compiler. Because i have only little knowledge about Java and it's compiler i can't tell if it's possible to alter / extend the compiler, maybe with a "preprocessor" or something.

Personally i love coroutines. As a Unity games developer i use them quite often. Because i play alot of Minecraft with ComputerCraft i was curious why coroutines in Lua (LuaJ) are implemented with threads.