Quasar might be the closest in the meantime. One problem is that blocking IO blocks all the green threads (fibers). It might be possible for Oracle or someone t

Quasar might be the closest in the meantime. One problem is that blocking IO blocks all the green threads (fibers). It might be possible for Oracle or someone to fix that by wrapping NIO with green threads to implement the IO APIs. Most people will just use async NIO wrapped in fibers so it appears synchronous. Also with Quasar any calls to Thread sleep, wait, or synchronization block all the threads. It would not be an easy feature for Oracle to add but Quasar has been attempting to get merged into the JRE. For Java 9 they said they got some features added that improves the situation but Quasar instrumentation will still be required. The Quasar instrumentation in my opinion is a pain. Out of the box you either get AoT instrumentation or you use Java agent command line option. Both were problematic for me in context of build processes, IDE support, etc. It's possible to do runtime instrumentation with no special command line option using the Quasar URL classloader and Ant task which scans classes to instrument.