timer-wheel: Add ‘timer-wheel-remove!’.

* fibers/timer-wheel.scm (timer-wheel-remove!): New procedure.

fibers/timer-wheel.scm

@@ -31,6 +31,7 @@
   #:use-module (ice-9 format)
   #:export (make-timer-wheel
             timer-wheel-add!
+            timer-wheel-remove!
             timer-wheel-next-entry-time
             timer-wheel-next-tick-start
             timer-wheel-next-tick-end
@@ -141,6 +142,18 @@
         (else
          (timer-wheel-add! (or outer (add-outer-wheel! wheel)) t obj)))))))
 
+(define (timer-wheel-remove! wheel entry)
+  "Remove @var{entry}, a timer entry as returned by @code{timer-wheel-add!},
+from @var{wheel}."
+  (match entry
+    (($ <timer-entry> prev next)
+     (when prev
+       (set-timer-entry-next! prev next)
+       (set-timer-entry-prev! entry #f))
+     (when next
+       (set-timer-entry-prev! next prev)
+       (set-timer-entry-next! entry #f)))))
+
 (define (timer-wheel-next-entry-time wheel)
   (define (slot-min-time head)
     (let lp ((entry (timer-entry-next head)) (min #f))