Venari/ML Interfaces and Examples
Authors: J.M. Wing, M. Faehndrich, N. Haines, K. Kietzke,
D. Kindred, J.G. Morrisett, and S. Nettles.
Appears as CMU-CS-93-123, March 1993.
The full text of this technical report is here (in
Transactions are a well-known and fundamental control abstraction that
the database community. Application programmers can
treat a sequence of operations as an atomic ("all-or-nothing") unit
and rely on the runtime environment to guarantee serializability of
concurrent transactions and persistence of effects of committed
transactions. In this report, we present interfaces, expressed in
Standard ML, for creating and controlling transactions. Unlike other
transaction-based high-level programming languages such as Argus and Avalon,
Venari/ML is the first
support multi-threaded transactions, where each
transaction may have multiple threads of control executing within its
scope. We present a set of simple examples that show how to use
Venari/ML interfaces individually and also in some useful
combinations. We also present a larger example of searching a
database of BibTeX entries. This report is intended primarily for
an SML programmer whose application requires transactional properties.
Our work on transactions in the context of SML led to our invention of
a new control abstraction, called a skein, which is a group of
threads that cooperate on a single task.
Skeins take as parameters
initialization and completion functions; transactions
are easily constructed as a special case of skeins.
The Venari/ML interfaces are cast in terms of SML's modules
facility. Modules support a separation of
concerns, e.g., persistence from undoability,
that are often tightly integrated in other
transaction-based programming languages.
We make extensive use of closures in SML, allowing
us at runtime to compose different functions, each of which
supports a different feature of transactions.