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Write Concurrency

When the 'edittable' operator is used to modify a table in place there could be a possibility of silmultaneous writing of a table by multiple users. That is, if two or more users, on the same computer or perhaps on different computers on a network, attempted to modify a given table with 'edittable' at the same time, the table could become corrupted. To prevent data corruption, write concurrency control is provided by the use of a lockfile. The lock is in effect whenever a user runs 'edittable' against the table.

The name of the lockfile is the name of the table being modified, with a suffix of ".lock." For example, a table named "main" would have a lockfile named "main.lock." The lockfile is placed in the same directory as the table itself and is removed after the modification process is complete, even if the operation is aborted with an INTERRUPT signal (CONTROL-C or <DEL>). When an attempt to use this utility is made and there is already a valid lockfile associated with the referenced table an error message is produced and the utility exits.