Note that this change doesn't represent any sort of design suggestion
or decision: It merely represents an attempt to codify the
dependencies between the parts of the code base. There's still lots
of work to be done to actually make user-accessible modules.
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.