[mcclim-devel] [bug] Asynchronous ID-CHOICE-ERROR -- CLX or McCLIM?

[Andy Hefner]

I just encountered the "Asynchronous ID-CHOICE-ERROR" myself tonight,
in my case when multiple mcclim applications (in multiple threads) on
one screen race to repaint. I don't know if it's related to Nikodemus'
test case, which doesn't make any use of threads (excluding the
omnipresent CLX event dispatching thread), but at least it's the same
error.

Attached is a patch to CLX intending to address a race condition when
multiple threads attempt to allocate a resource ID -
DISPLAY-RESOURCE-ID-COUNT is incremented, but there is no locking to
protect the slot, resulting in intermittent duplicate IDs and
subsequent ID-CHOICE-ERROR. I've wrapped the allocation in a
with-display, and done the same to the nearby
deallocate-resource-id-internal for good measure. This should protect
the incf in resourcealloc, the (setf gethash) in save-id, and the
remhash in deallocate-resource-id-internal.

--- old-clx/display.lisp        2008-08-21 23:27:35.000000000 -0400
+++ new-clx/display.lisp        2008-08-21 23:27:35.000000000 -0400
@@ -155,11 +155,12 @@

 (defmacro allocate-resource-id (display object type)
   ;; Allocate a resource-id for OBJECT in DISPLAY
-  (if (member (eval type) +clx-cached-types+)
-      `(let ((id (funcall (display-xid ,display) ,display)))
-        (save-id ,display id ,object)
-        id)
-    `(funcall (display-xid ,display) ,display)))
+  `(with-display (,display)
+     ,(if (member (eval type) +clx-cached-types+)
+          `(let ((id (funcall (display-xid ,display) ,display)))
+             (save-id ,display id ,object)
+             id)
+          `(funcall (display-xid ,display) ,display))))

 (defmacro deallocate-resource-id (display id type)
   ;; Deallocate a resource-id for OBJECT in DISPLAY
@@ -167,7 +168,8 @@
     `(deallocate-resource-id-internal ,display ,id)))

 (defun deallocate-resource-id-internal (display id)
-  (remhash id (display-resource-id-map display)))
+  (with-display (display)
+    (remhash id (display-resource-id-map display))))

 (defun lookup-resource-id (display id)
   ;; Find the object associated with resource ID
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