It is certainly the plan that existing code should work with little or no modification. Alan Bateman has been doing great work fixing the standard library to al

It is certainly the plan that existing code should work with little or no modification. Alan Bateman has been doing great work fixing the standard library to allow this, though there will be some limitations round JNI and other areas. If you need to stop too many fibers running at once then this should be very simple to implement using any of java.util.concurrent’s mechanisms, if they block the fiber it will be parked and another can be run.