Operating Systems: Concurrent and Distributed Software Design

15.4. Idempotent (repeatable) operations

In certain simple cases it is possible to ensure that an operation can be repeated without causing any errors or inconsistencies. When deciding how certain operations should be specified, for example the form their arguments should take, it may be possible to choose an idempotent implementation. For example, the repeatable method of writing a sequence of bytes to the end of a file is to specify the precise byte position at which the new bytes should be written and make this an argument of an 'append' operation. If an append operation is relative to a system-maintained pointer, the bytes could be written more than once if the operation was repeated. It is not always possible to achieve repeatable operations. ...