Concurrent group update leads to duplicate members

1. install Nuxeo
2. start Nuxeo
3. create an empty group:

   curl -H 'Content-Type:application/json+nxrequest' -X POST -d '{"params":{"groupname":"mytestgroup","members":[]},"context":{}}'   -u Administrator:Administrator http://localhost:8080/nuxeo/api/v1/automation/Group.CreateOrUpdate
   

1. double-check it is empty:

   curl -s -H 'Content-Type:application/json+nxrequest' -X GET -H "fetch.group: memberUsers,memberGroups" -u Administrator:Administrator http://localhost:8080/nuxeo/api/v1/group/mytestgroup | jq .
   {
     "entity-type": "group",
     "groupname": "mytestgroup",
     "grouplabel": "mytestgroup",
     "id": "mytestgroup",
     "properties": {
       "tenantId": null,
       "description": null,
       "grouplabel": null,
       "groupname": "mytestgroup"
     },
     "memberUsers": [],
     "memberGroups": []
   

1. now add twice the member through 2 concurrent requests:

   curl -H 'Content-Type:application/json+nxrequest' -X POST -d '{"params":{"groupname":"mytestgroup","members":["Administrator"]},"context":{}}' -u Administrator:Administrator http://localhost:8080/nuxeo/api/v1/automation/Group.CreateOrUpdate & curl -H 'Content-Type:application/json+nxrequest' -X POST -d '{"params":{"groupname":"mytestgroup","members":["Administrator"]},"context":{}}'   -u Administrator:Administrator http://localhost:8080/nuxeo/api/v1/automation/Group.CreateOrUpdate &
   

1. observe the group now contains twice the same user:

   curl http://localhost:8080/nuxeo/api/v1/group/mytestgroup | jq .
   {
     "entity-type": "group",
     "groupname": "mytestgroup",
     "grouplabel": "mytestgroup",
     "id": "mytestgroup",
     "properties": {
       "tenantId": null,
       "description": null,
       "grouplabel": null,
       "groupname": "mytestgroup"
     },
     "memberUsers": [
       "Administrator",
       "Administrator"
     ],
     "memberGroups": []
   }
   

Note: this does not happen when trying to add twice the same user in a single request:

curl -H 'Content-Type:application/json+nxrequest' -X POST -d '{"params":{"groupname":"administrators","members":["Administrator","Administrator"]},"context":{}}'   -u Administrator:Administrator http://localhost:8080/nuxeo/api/v1/automation/Group.CreateOrUpdate