PS - OO : Object Locking, Object Callback

• Client Read Request for an Object :
  • If the requested object cached locally then local read else request object, page from server.
  • Server sends the page when the read lock can be granted on the object.
    • Objects on the page, which are write locked by other clients marked as unavailable and the remaining objects are considered to be cached at clients.
  • Client receives page, merges the changes if the page is already cached locally by the client. On merging care is taken that the updated objects (by the client) are not overwritten by those from the read page.
• Client Write Request for an Object :
  • Server calls back the object locks from all other clients that contain the object.
    • Clients releasing the cached copy, mark the object as unavailable.
  • Server grants lock to client.
  • Server maintains information of cached copies at object level.