Persistence + Undoability = Transactions

著者: Scott M. Nettles, Jeannette M. Wing
タイトル: Persistence + Undoability = Transactions
日時: Aug 1991
概要: Persistence means objects live potentially forever. Undoability means that any change to program's store can potentially be undone. In our design and implementation of support for single-threaded nested transactions in standard ML of New Jersey (SML/NJ), we provide persistence and undoability as orthogonal features and combine them in a simple and elegant manner. We provide support for persistence through an SML interface that lets users manipulate a set of persistent roots and provides a save function that causes all data reachable from the persistent roots to be moved into the persistent heap. We implement the interface through simple extensions to SML's generational collector and maintain the persistent heap using CMU's Recoverable Virtual Memory system. We provide support for undoability through an SML interface that exports two functions: checkpoint, which checkpoint the current store, and restore, which undoes all changes made to the previously checkpointed store. The implementation takes advantage of the simple runtime representation of data in SML and, as for persistence, extends the existing garbage collector scheme. SML's "mostly" function nature allows us to implement this abstraction without undue performance penalty. Finally, we combine these capabilities to support single- threaded nested transactions by defining a higher-order function transact that guarantees the permanence of effects of committed transactions. We succinctly define transact completely in terms of the interfaces for persistence and undoability. Unlike other transaction-based programming languages like Argus or Avalon/C*, we need not add new control structures; moreover, we handle aborts of nested or top-level transactions using SML's exception mechanism.
カテゴリ: CMUTR

Category: CMUTR Institution: Department of Computer Science, Carnegie Mellon University Abstract: Persistence means objects live potentially forever. Undoability means that any change to program's store can potentially be undone. In our design and implementation of support for single-threaded nested transactions in standard ML of New Jersey (SML/NJ), we provide persistence and undoability as orthogonal features and combine them in a simple and elegant manner. We provide support for persistence through an SML interface that lets users manipulate a set of persistent roots and provides a save function that causes all data reachable from the persistent roots to be moved into the persistent heap. We implement the interface through simple extensions to SML's generational collector and maintain the persistent heap using CMU's Recoverable Virtual Memory system. We provide support for undoability through an SML interface that exports two functions: checkpoint, which checkpoint the current store, and restore, which undoes all changes made to the previously checkpointed store. The implementation takes advantage of the simple runtime representation of data in SML and, as for persistence, extends the existing garbage collector scheme. SML's "mostly" function nature allows us to implement this abstraction without undue performance penalty. Finally, we combine these capabilities to support single- threaded nested transactions by defining a higher-order function transact that guarantees the permanence of effects of committed transactions. We succinctly define transact completely in terms of the interfaces for persistence and undoability. Unlike other transaction-based programming languages like Argus or Avalon/C*, we need not add new control structures; moreover, we handle aborts of nested or top-level transactions using SML's exception mechanism. Number: CMU-CS-91-173 Bibtype: TechReport Month: Aug Author: Scott M. Nettles Jeannette M. Wing Title: Persistence + Undoability = Transactions Year: 1991 Address: Pittsburgh, PA Super: @CMUTR