An Exclusive or Batch oplock is an exclusive (read-write/deny-all) file lock that an SMB client may obtain at the time it opens a file. The server grants the oplock only if no other application is currently accessing the file.
When a client owns an Exclusive or Batch oplock on a file, it can cache part or all of the file locally. Any changes that the client makes to the file are also cached locally. Changes do not need to be written to the server until the client releases the oplock. In the case of an Exclusive oplock, the client releases the oplock when the server requests that it does so, or when it closes the file. In the case of a Batch oplock, the client may keep information (including changes) locally even after closing the file. While the client has an Exclusive or Batch oplock on a file, the server guarantees that no other client may access the file.
If a client requests access to a file that has an Exclusive or Batch oplock, the server asks the client with the oplock to release it. The client then writes the changes to the server and releases the oplock. Once this operation has finished, the server allows the second client to access the file. This happens regardless of the second client’s network protocol.
In cases where an SMB client requests an oplock on a file that has an Exclusive or Batch oplock, the server breaks the existing oplock and grants both clients Level II oplocks instead.