Index: openacs-4/packages/acs-tcl/tcl/defs-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/defs-procs.tcl,v
diff -u -r1.81.2.29 -r1.81.2.30
--- openacs-4/packages/acs-tcl/tcl/defs-procs.tcl	6 Aug 2024 17:25:04 -0000	1.81.2.29
+++ openacs-4/packages/acs-tcl/tcl/defs-procs.tcl	8 Aug 2024 14:30:53 -0000	1.81.2.30
@@ -523,6 +523,33 @@
         nsv_set ad_param . .
     }
 
+    ad_proc -private ad_parameter_cache_flush_dict {
+        key
+        parmeter_name
+    } {
+        Flush a single value from the nsv cache.
+
+        This proc is necessary in cases, where a node writes a new
+        parameter value before it has read the old one.
+
+        Since a plain "nsv_dict unset ad_param $key $parameter_name"
+        raises an exception, when the pair does not exist, and we do
+        not want to allow in cluster requests arbitrary "catch"
+        commands, we allow "ad_parameter_cache_flush_dict" instead.
+        Probably, the best solution is to add support for
+
+            nsv_dict unset -nocomplain -- ad_param $key $parameter_nam
+
+        The existing nsv_dict was built after Tcl's "dict unset",
+        which does not have the "-nocomplain" option either. However,
+        an atomic operation would certainly be preferable over an exists/unset
+        pair, which is no acceptable solution.
+
+    } {
+        catch {nsv_dict unset ad_param $key $parameter_name}
+    }
+
+
     ad_proc -public ad_parameter_cache {
         -set
         -delete:boolean
@@ -542,9 +569,7 @@
 
     } {
         if {$delete_p} {
-            if {[nsv_dict exists ad_param $key $parameter_name]} {
-                ::acs::clusterwide nsv_dict unset ad_param $key $parameter_name
-            }
+            acs::clusterwide ad_parameter_cache_flush_dict $key $parameter_name
             acs::per_request_cache flush -pattern acs-tcl.ad_param-$key
             return
         }