Stale state protection service may not work under specific interleaving

[project-concerto]

StaleStateProtectionService is used to prevent admin from modify based on stale page. When admin try to send a request to modify some data, the token of page he observed will be attached with the request, so that server can check whether this admin try to modify the data based on the stale page.

However, the validation and update is not executed atomically, which means following interleaving may occur and cause wrong state. Admin2 modified the data based on stale page and the modification of Admin1 may be overwritten.

Admin 1	Admin 2
get Page+Token	get Page + Token
token validation passed
	token validation passed
modify data in Page
	modify data in Page