[clhodapp]

I think that's not quite it:

I believe that loom is implementing cooperative lightweight threads and simultaneously reworking all of the blocking IO operations in the Java standard library to include yields. I guess this means that you could, for example, hold an OS-level thread forever by writing an infinite loop that doesn't do any IO...

[kaba0]

I believe both the OS and the JVM is free to reschedule it. Yields are just an explicit way of possibly changing the thread.