As a sanity check I reran the above on a different machine, with the latest beta including the latest new core, and got the following output. The ^C is after waiting for 10 seconds.
Running ./asynctest
[main(----) INF] Listening for requests on http://127.0.0.1:8080/
[main(----) INF] Please open http://127.0.0.1:8080/ in your browser.
[vibe-0(OLhj) INF] Starting to compute value in worker task.
[vibe-0(OLhj) INF] start waiting
[vibe-0(OLhj) INF] running 0
[main(WqEv) INF] Starting computation in main task
[vibe-0(OLhj) INF] running 3
[vibe-0(OLhj) INF] running 4
[vibe-0(OLhj) INF] running 7
[vibe-0(OLhj) INF] running 8
[vibe-0(OLhj) INF] running 10
[vibe-0(OLhj) INF] running 11
[vibe-0(OLhj) INF] running 14
.
.
.
[vibe-0(OLhj) INF] running 191
[vibe-0(OLhj) INF] running 193
[vibe-0(OLhj) INF] running 195
[vibe-0(OLhj) INF] running 196
[vibe-0(OLhj) INF] running 198
[vibe-0(OLhj) INF] running 200
[main(WqEv) INF] Finished computation in main task. Waiting for async value.
^C[main(WqEv) INF] [main(----) INF] Received signal 2. Shutting down.
carl@carl1604:~/Documents/vibed/asynctest$ fuser 8080/tcp
8080/tcp: 5063
carl@carl1604:~/Documents/vibed/asynctest$ kill 5063
[main(----) INF] Received signal 15. Shutting down.
carl@carl1604:~/Documents/vibed/asynctest$ fuser 8080/tcp
8080/tcp: 5063
The 200.msecs computation in the main task completes, calls getResult on the worker task, which promptly hangs, not continuing printing out its execution times until 500.msecs and terminating with the log message "Finished computing value in worker task.". The resulting hung process cannot be terminated by ordinary means.