Pull out event-handling stub, to show where future hooks will go

simple-udp-service.rkt

@@ -4,6 +4,7 @@
 
 (require racket/match)
 (require racket/udp)
+(require (only-in srfi/1 append-reverse))
 (require "dump-bytes.rkt")
 
 (provide (struct-out udp-packet)
@@ -53,9 +54,9 @@
 		      (values '() state)))
 	      event-handlers))
 
-  (define (dispatch-events events old-state)
+  (define (dispatch-events events next-events-rev old-state)
     (if (null? events)
-	(read-and-dispatch old-state)
+	(check-for-io (reverse next-events-rev) old-state)
 	(let ((classified-packet (car events)))
 	  (define-values (new-events new-state)
 	    (let search ((handlers event-handlers))
@@ -63,20 +64,29 @@
 	       [(null? handlers) (default-handler classified-packet old-state)]
 	       [((caar handlers) classified-packet) ((cdar handlers) classified-packet old-state)]
 	       [else (search (cdr handlers))])))
-	  (dispatch-events (append (cdr events) new-events) new-state))))
+	  (dispatch-events (cdr events)
+			   (append-reverse new-events next-events-rev)
+			   new-state))))
 
-  (define (read-and-dispatch old-state)
+  (define (check-for-io pending-events old-state)
     (define buffer (make-bytes packet-size-limit))
-    (define-values (packet-length source-hostname source-port)
-      (udp-receive! s buffer))
-    (define packet (subbytes buffer 0 packet-length))
+    (define new-events
+      (sync (handle-evt (udp-receive!-evt s buffer)
+			(match-lambda
+			 [(list packet-length source-hostname source-port)
+			  (define packet (subbytes buffer 0 packet-length))
+			  (printf ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>~n~v~n" packet)
+			  (dump-bytes! buffer packet-length)
+			  (flush-output)
 
-    (printf ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>~n~v~n" packet)
-    (dump-bytes! buffer packet-length)
-    (flush-output)
+			  (define packet-and-source
+			    (udp-packet packet source-hostname source-port))
+			  (define classified-packet (packet-classifier packet-and-source))
+			  (list classified-packet)]))
+	    (if (null? pending-events)
+		never-evt ;; Nothing waiting to be done, don't wake up until sth external arrives
+		(handle-evt (system-idle-evt)
+			    (lambda (dummy) '())))))
+    (dispatch-events (append new-events pending-events) '() old-state))
 
-    (define packet-and-source (udp-packet packet source-hostname source-port))
-    (define classified-packet (packet-classifier packet-and-source))
-    (dispatch-events (list classified-packet) old-state))
-
-  (read-and-dispatch initial-state))
+  (check-for-io '() initial-state))