declare namespace xmldb="http://exist-db.org/xquery/xmldb";
declare namespace util="http://exist-db.org/xquery/util";

declare function local:update() as element()*
{
let $maxId := max(for $i in //node/@id return xs:integer($i)) + 1
let $collection := xmldb:collection('xmldb:exist:///db/C1', 'guest', 'guest')
let $update1 :=
  <xu:modifications xmlns:xu="http://www.xmldb.org/xupdate" version="1.0">
    <xu:append select="doc('/db/C1/test.xml')/root">
      <node id="{$maxId}">appended node - guest A</node>
    </xu:append>
  </xu:modifications>
let $update2 :=
  <xu:modifications xmlns:xu="http://www.xmldb.org/xupdate" version="1.0">
    <xu:append select="doc('/db/C1/test2.xml')/root">
      <node id="{$maxId}">appended node - guest B</node>
    </xu:append>
  </xu:modifications>
return
  <test>
   {$maxId},{xmldb:update($collection, $update1)},{xmldb:update($collection, $update2)}
  </test>
};

for $i in (1,2,3,4,5,6,7,8,9,10)
let $doc := (doc('/db/C1/test.xml'),doc('/db/C1/test2.xml'))
let $j := util:exclusive-lock($doc,local:update() )
let $k := util:exclusive-lock($doc,local:update() )
return ($j,$k)