Buffer and locks available in memory
The simplest read operation occurs when the data is already available in memory because either it is prefetched or because it has been read recently by another read call.
In either case, the buffer is locally locked and the data is copied to the application data area. The lock is released when the copy is complete. Note that no token communication is required because possession of the buffer implies that the node at least has a read token that includes the buffer. After the copying, prefetching is initiated if appropriate.