Maintaining data consistency in a cache system

Each time a connecting z/TPF system tries to read or write data, the interest of that z/TPF system is registered in that piece of shared data. It also indicates, in a local cache vector entry the z/TPF system specifies, that the copy of the piece of shared data is valid. A valid copy of data is one that contains the latest updates to that piece of shared data that other z/TPF systems might have made.

Registering interest allows the z/TPF system to remember that the local cache buffer contains a valid copy of the piece of shared data. If that piece of shared data is changed, the z/TPF system deregisters interest in that piece of shared data for the others and indicates in their local cache vector entry that the copy is no longer valid. Each connecting z/TPF system must ensure that the locally cached copy is valid by testing the vector entry associated with that piece of shared data. Each z/TPF system also needs to ensure that there is serialization of the data between the time the z/TPF system tests the validity of the piece of shared data and the time when the z/TPF system makes use of the data.