Index: openacs-4/packages/xotcl-core/tcl/05-db-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/xotcl-core/tcl/05-db-procs.tcl,v
diff -u -r1.148.2.29 -r1.148.2.30
--- openacs-4/packages/xotcl-core/tcl/05-db-procs.tcl	5 Jan 2021 09:38:55 -0000	1.148.2.29
+++ openacs-4/packages/xotcl-core/tcl/05-db-procs.tcl	24 Jan 2021 19:54:13 -0000	1.148.2.30
@@ -295,6 +295,7 @@
   ::xo::db::Driver abstract instproc list           {{-dbn ""} {-bind ""} -prepare qn sql}
   ::xo::db::Driver abstract instproc dml            {{-dbn ""} {-bind ""} -prepare qn sql}
   ::xo::db::Driver abstract instproc foreach        {{-dbn ""} {-bind ""} -prepare qn sql {script}}
+  ::xo::db::Driver abstract instproc row_lock       {{-dbn ""} {-bind ""} {-for "UPDATE"} -prepare qn sql}  
   ::xo::db::Driver abstract instproc transaction    {{-dbn ""} script args}
   ::xo::db::Driver abstract instproc ds {onOff}
   ::xo::db::Driver abstract instproc prepare        {-handle {-argtypes ""} sql}
@@ -553,6 +554,16 @@
     uplevel [list ::db_list [uplevel [list [self] qn $qn]] $sql {*}$bindOpt]
   }
 
+  ::xo::db::DB instproc row_lock {{-dbn ""} {-bind ""} {-for "UPDATE"} -prepare qn sql} {
+    #
+    # PostgreSQL has several variants of row-level lock modes (the
+    # "for" part), but other database systems just support only "FOR
+    # UPDATE", which should work always. Therefore, ignore for other
+    # DB-systems the specified value and use just "FOR UPDATE".
+    #
+    :uplevel [list ::xo::dc list -dbn $dbn -bind $bind $qn "$sql FOR UPDATE"]
+  }
+
   proc ::xo::db::pg_0or1row {sql} {
     ns_log notice "::xo::db::pg_0or1row deprecated"
     ::db_with_handle h {
@@ -643,6 +654,11 @@
     return [db_resultrows]
   }
 
+  ::xo::db::DB-postgresql instproc row_lock {{-dbn ""} {-bind ""} {-for "UPDATE"} -prepare qn sql} {
+    set prepareOpt [expr {[info exists prepare] ? [list -prepare $prepare] : ""}]
+    :uplevel [list ::xo::dc list -dbn $dbn -bind $bind {*}$prepareOpt $qn "$sql FOR $for"]
+  }
+  
   ::xo::db::DB-postgresql instproc prepare {-handle:required {-argtypes ""} sql} {
     #
     # Define a md5 key for the prepared statement in nsv based on the
Index: openacs-4/packages/xotcl-core/tcl/cr-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/xotcl-core/tcl/cr-procs.tcl,v
diff -u -r1.76.2.36 -r1.76.2.37
--- openacs-4/packages/xotcl-core/tcl/cr-procs.tcl	6 Dec 2020 08:21:09 -0000	1.76.2.36
+++ openacs-4/packages/xotcl-core/tcl/cr-procs.tcl	24 Jan 2021 19:54:13 -0000	1.76.2.37
@@ -1001,6 +1001,10 @@
     }
 
     ::xo::dc transaction {
+      ::xo::dc row_lock -for "no key update" -prepare integer item_lock {
+        select item_id from cr_items where item_id = :item_id
+      }
+      
       [:info class] instvar storage_type
       set revision_id [xo::dc nextval acs_object_id_seq]
       if {$storage_type eq "file"} {
@@ -1036,18 +1040,27 @@
         # If we do not make the revision live, use the old
         # revision_id, and let CrCache save it ......
         #
-        # TODO: is this still needed? comment out for testing
-        #
-        #set revision_id $old_revision_id
       }
+      
+      #
+      # Update instance variables "modifying_user" and "last_modified"
+      # from potentially changed DB values.
+      #
       set :modifying_user $creation_user
       ::xo::dc 1row -prepare integer get_metadata {
         select context_id, last_modified
         from acs_objects where object_id = :revision_id
       }
       set :last_modified $last_modified
-      if {[info exists :context_id] &&
-          $context_id != ${:context_id}} {
+      
+      #
+      # In case the context_id has in the DB is different as in the
+      # instance variable, push the value from the instance variable
+      # to the DB as well.
+      #
+      if {[info exists :context_id]
+          && $context_id != ${:context_id}
+        } {
         set context_id ${:context_id}
         ::xo::dc dml update_context {
           update acs_objects