Scheme 48 1.0.1.
Namely, instead of associating a list of queues with every thread, we
associate a single cell, holding the thread. That cell is stored in
thread queues, and once a thread is made runnable again, the cell is
set to #f. The thread-queue accessors ignore cells containing #f.
Implement an experimental OBTAIN-LOCK-MULTIPLE to test the whole
thing.
These can be used (together with fluids) to implement something akin
to PLT's and Chez's parameters for holding thread-local state such as
CWD, syslog channel, etc.