check existence of sessions in some locking areas

scheme/httpd/surflets/surflet-handler.scm

@@ -316,9 +316,11 @@
   ;; surveillance of killing new session that has the same number by
   ;; accident)
   (let ((session (table-ref *session-table* session-id)))
-    (memo-killed! (session-memo session)))
-  ;; why can't table entries be deleted correctly?
-  (table-set! *session-table* session-id #f)
+    (if session
+	(begin
+	  (memo-killed! (session-memo session))
+	  (table-set! *session-table* session-id #f))))
+	;; else: somebody was faster than we
   (release-lock *session-table-lock*))
  
 ;;; SESSION-ADJUST-TIMEOUT!
@@ -330,17 +332,21 @@
 
 (define (really-session-adjust-timeout! session-id time-to-live)
   (obtain-lock *session-table-lock*)
-  (let* ((session (table-ref *session-table* session-id))
-	 (memo (session-memo session))
+  (let ((session (table-ref *session-table* session-id))
 	(new-memo (make-default-memo)))
+    (if session
+	(let ((memo (session-memo session)))
 	  ;; Do it this way: new values and then new message
 	  (set-memo:value memo 
 			  (+ (time) time-to-live))
 	  (set-memo:new-memo memo new-memo)
 	  ;; I don't think we need locking here. Do you agree?
 	  (set-session-memo! session new-memo)
-    (set-memo:message memo 'adjust-timeout))
+	  (set-memo:message memo 'adjust-timeout)
 	  (release-lock *session-table-lock*))
+	(begin
+	  (release-lock *session-table-lock*)
+	  (error "There is no session with this ID" session-id)))))
 
 ;;; ADJUST-TIMEOUT!
 ;; Resets time-to-die of current session. The argument must be
@@ -522,13 +528,13 @@
 ;;; RESET-SURFLET-CACHE!
 ;; Clears *SURFLET-TABLE* (locking).
 (define (reset-surflet-cache!)
-  (with-fatal-handler
-   (lambda (condition decline)
-     (release-lock *surflet-table-lock*)
-     (decline))
+;  (with-fatal-handler
+;   (lambda (condition decline)
+;     (release-lock *surflet-table-lock*)
+;     (decline))
    (obtain-lock *surflet-table-lock*)
    (set! *surflet-table* (make-string-table))
-   (release-lock *surflet-table-lock*)))
+   (release-lock *surflet-table-lock*))
 
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 ;;; INSTANCE