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Pessimistic Reading

If $CT \! B$$>$0 then f must be and remain consistent (with the server version) within the specified time bound. For example, with $CT \! B$=2 hours (from now), then f must be guaranteed to be and remain consistent until 12.00. In other words, f must not have been updated on the server between 9.00 (where it was cached) and 10.00 (which is now), and furthermore, it must not be updated on the server (by other clients) for the next two hours.

If f has been updated between 9.00 and 10.00 then a new copy of it is required, for it to be consistent now. Under any circumstance a readlock must be obtained, for it to remain consistent within the next two hours. Locking of files are dealt with in Section 5.4.

If obtaining a new copy of f or a readlock on it (or both) succeeds then the open succeeds, otherwise it fails.

Using $CT \! B$$>$0 the client is pessimistic. The greater the $CT \! B$ the higher the degree of pessimism.

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