io-wakeup: Use file descriptors when calling select.

Rather than ports, since select doesn't work for all ports in Guile.

* fibers/io-wakeup.scm (readable?, writable?, try-ready): Take a fd
rather than a port.
(wait-until-port-readable-operation,
wait-until-port-writable-operation): Pass the fd to try-ready?.

fibers/io-wakeup.scm

@@ -51,21 +51,21 @@
 
 ;; These procedure are subject to spurious wakeups.
 
-(define (readable? port)
+(define (readable? fd)
   "Test if PORT is writable."
-  (match (select (vector port) #() #() 0)
+  (match (select (vector fd) #() #() 0)
     ((#() #() #()) #f)
     ((#(_) #() #()) #t)))
 
-(define (writable? port)
+(define (writable? fd)
   "Test if PORT is writable."
-  (match (select #() (vector port) #() 0)
+  (match (select #() (vector fd) #() 0)
     ((#() #() #()) #f)
     ((#() #(_) #()) #t)))
 
-(define (try-ready ready? port)
+(define (try-ready ready? fd)
   (lambda ()
-    (and (ready? port) values)))
+    (and (ready? fd) values)))
 
 (define (make-wait-operation try-fn schedule-when-ready port port-ready-fd)
   (letrec ((this-operation
@@ -110,11 +110,11 @@ of the operation."
 
 (define (wait-until-port-readable-operation port)
   "Make an operation that will succeed when PORT is readable."
-  (make-read-operation (try-ready readable? port) port))
+  (make-read-operation (try-ready readable? (port-read-wait-fd port)) port))
 
 (define (wait-until-port-writable-operation port)
   "Make an operation that will succeed when PORT is writable."
-  (make-write-operation (try-ready readable? port) port))
+  (make-write-operation (try-ready readable? (port-write-wait-fd port)) port))
 
 (define (with-x-waiting-is-failure port current-x-waiter try-fn)
   "Return a thunk like TRY-FN, except that it also fails when