maybe-commit-and-make-ready-and-block

It would be nice if Scheme48 had a procedure that would atomically (1)
maybe commit the current proposal, (2) make a thread or a queue of
threads ready, and (3) block on a cell.  That way, it would not be
impossible to correctly implement an operation to atomically unlock a
mutex (other than a spin mutex) and wait on a condition variable.  The
definition would look something like this:

(define (maybe-commit-and-block-and-make-ready cell thread-or-queue)
  (disable-interrupts!)
  (cond ((maybe-commit)
         (if (queue? thread-or-queue)
             (make-threads-ready thread-or-queue)
             (make-ready thread-or-queue))
         (set-thread-cell! (current-thread) cell)
         (suspend-to (thread-scheduler (current-thread))
                     (list (enum event-type blocked)))
         #t)
        (else
         (enable-interrupts!)
         #f)))

However, just calling MAKE-THREADS-READY or MAKE-READY as-is breaks
down here, because those call MAYBE-SUSPEND, rendering the operation
non-atomic.

Also, for unrelated reasons, it would be nice if this operation (and
all the MAYBE-COMMIT-AND-* operations: MAYBE-COMMIT-AND-BLOCK, &c.)
left the enabled interrupts alone if the commit failed, rather than
enabling all interrupts.  This is what MAYBE-COMMIT-NO-INTERRUPTS
already does.