Version management system using plural control fields for synchronizing two versions of files in a multiprocessor system

摘要

In a data processing system that stores a first and second version of a given data set, a method for synchronizing the first and second versions comprises steps of maintaining a sync-complete control field and a sync-in-progress control field in the inode of each of the first and second versions. Write accesses to the versions are modified so that the sync-complete control field and the sync-in-progress control field are cleared in response to any change in the associated version. The sync- complete control bits for the first and second versions are tested, and if either or both are cleared, then the sync-in-progress control field associated with a select source version is set. Next, a copy of the source version is transferred to a temporary file. After the transfer is complete, the sync-in-progress control field in the source version is tested, and if it is set when the temporary version is complete, then the sync-complete control field is set and the sync-in- progress control field is cleared in the source versions. Next, the sync- complete control field is set in the temporary version. Finally, the temporary version is renamed to the other of the first and second versions and the original other version is removed.