In the current HEAD of master, thread-interrupt! doesn't seem to consider interrupt-level. Is there uncommitted code? I see that the implementation strategy varies greatly depending on the actual thread implementation, but if would help at least to list outlines of possible strategies in the comment, rather than current "TODO" list.

Here are a few strategies I can think of. Let me know if there are more clever ways.

- If you have your own thread scheduler, you can check the status at the time of context switch. Unfortunately this doesn't apply for native threads.

- Check the status at some specific points, e.g. at the entrance of procedures, or before a blocking system calls.

- Employ a coarse interval timer and check the status periodically.

(Initially, I thought I could use Gauche's signal handling mechanism, in which a native signal handler just set a flag, and the VM checks the flag between VM instructions. But I realized that, for interrupts, the VM also needed to get current-interrupt-level, which would be a lot heaviler than just read a flag.)