An EVACS simulation with nested transactions

Documented here is the recent effort of the MISSION Kernel Team on an Extra-Vehicular Activity Control System (EVACS) simulation with nested transactions. The team has implemented the EVACS simulation along with a design for nested transactions. The EVACS simulation is a project wide aid to exploring Mission and Safety Critical (MASC) applications and their support software. For this effort it served as a trial scenario for demonstrating nested transactions and exercising the transaction support design. The EVACS simulation is a simulation of some aspects of the Extra-Vehicular Activity Control System, in particular, just the selection of communication frequencies. Its current definition is quite narrow, serving only as a starting point for prototyping purposes. (EVACS itself may be supplanted in a larger scenario of a lunar outpost with astronauts and a lunar rover.) Initially the simulation of frequency selection was written without consideration of nested transactions. This scenario was then modified to embed its processing in nested transactions. To simplify the prototyping effort, only two aspects of the general design for transaction support have been implemented: the basic architecture and state recovery. The simulation has been implemented in the programming language Smalltalk. It consists of three components: (1) a simulation support code which provides the framework for initiating, interacting and tracing the system; (2) the EVACS application code itself, including its calls upon nested transaction support; and (3) a transaction support code which implements the logic necessary for nested transactions. Each of these components deserves further description, but for now only the transaction support is discussed

A Lazy Approach for Supporting Nested Transactions

Transactional memory (TM) is a compelling alternative to traditional synchronization, and implementing TM primitives directly in hardware offers a potential performance advantage over software-based methods. In this paper, we demonstrate that many of the actions associated with transaction abort and commit may be performed lazily -- that is, incrementally, and on demand. This technique is ideal for hardware, since it requires little space or work; in addition, it can improve performance by sparing accesses to committing or aborting locations from having to stall until the commit or abort completes. We further show that our lazy abort and commit technique supports open nesting and orElse, two language-level proposals which rely on transactional nesting. We also provide design notes for supporting lazy abort and commit on our own hardware TM system, based on VTM

A Java implementation of a Linda-like Tuplespace system with nested transactions : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Computer Science at Massey University, Albany, New Zealand

The Tuplespace model is considered a powerful option for the design and implementation of loosely coupled distributed systems. In this report, the features of the Tuplespace model are examined as well as the issues involved in implementing such a Tuplespace system based on Java. The system presented includes the function of Transactions: a collection of operations that either all succeed or all fail. The system also permits Nested Transactions: an extension of transactions. Nested transactions have a multi-level grouping structure: each nested transaction consists of zero or more operations and possibly some nested transactions. The key advantages offered by nested transactions include that they enable the failure of an operation to be isolated within a certain scope without necessarily aborting the entire transaction, and they allow programmers to sub-divide a complex operation into a number of smaller and simpler concurrent operations. The other features of nested transactions are also examined in this report. Finally, the testing results indicate that it is possible to build an efficient, scalable, and transaction secured distributed application that relies on the Tuplespace model and the system developed for this research

Timestamp ordering and nested transactions

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Bibliography: leaf 66.by James D. Aspnes.M.S

Mission and Safety Critical (MASC): An EVACS simulation with nested transactions

The Extra-Vehicular Activity Control System (EVACS) Simulation with Nested Transactions, a recent effort of the MISSION Kernel Team, is documented. The EVACS simulation is a simulation of some aspects of the Extra-Vehicular Activity Control System, in particular, just the selection of communication frequencies. The simulation is a tool to explore mission and safety critical (MASC) applications. For the purpose of this effort, its current definition is quite narrow serving only as a starting point for prototyping purposes. (Note that EVACS itself has been supplanted in a larger scenario of a lunar outpost with astronauts and a lunar rover). The frequency selection scenario was modified to embed its processing in nested transactions. Again as a first step, only two aspects of transaction support were implemented in this prototype: architecture and state recovery. Issues of concurrency and distribution are yet to be addressed

Safe Open-Nested Transactions Through Ownership

Researchers in transactional memory (TM) have proposed open nesting asa methodology for increasing the concurrency of a program. The ideais to ignore certain "low-level" memory operations of anopen-nested transaction when detecting conflicts for its parenttransaction, and instead perform abstract concurrency control for the"high-level" operation that nested transaction represents. Tosupport this methodology, TM systems use an open-nested commitmechanism that commits all changes performed by an open-nestedtransaction directly to memory, thereby avoiding low-levelconflicts. Unfortunately, because the TM runtime is unaware of thedifferent levels of memory, an unconstrained use of open-nestedcommits can lead to anomalous program behavior.In this paper, we describe a framework of ownership-awaretransactional memory which incorporates the notion of modules into theTM system and requires that transactions and data be associated withspecific transactional modules or Xmodules. We propose a newownership-aware commit mechanism, a hybrid between anopen-nested and closed-nested commit which commits a piece of datadifferently depending on whether the current Xmodule owns the data ornot. Moreover, we give a set of precise constraints on interactionsand sharing of data among the Xmodules based on familiar notions ofabstraction. We prove that ownership-aware TM has has cleanmemory-level semantics and can guarantee serializability bymodules, which is an adaptation of multilevel serializability fromdatabases to TM. In addition, we describe how a programmer canspecify Xmodules and ownership in a Java-like language. Our typesystem can enforce most of the constraints required by ownership-awareTM statically, and can enforce the remaining constraints dynamically.Finally, we prove that if transactions in the process of aborting obeyrestrictions on their memory footprint, the OAT model is free fromsemantic deadlock

Intervention Policy of the BoJ: A Unified Approach

Intervening in the FX market implies a complex decision process for central banks. Monetary authorities have to decide whether to intervene or not, and if so, when and how. Since the successive steps of this procedure are likely to be highly interdependent, we adopt a nested logit approach to capture their relationships and to characterize the prominent features of the various steps of the intervention decision. Our findings shed some light on the determinants of central bank interventions, on the so-called secrecy puzzle and on the identification of the variables influencing the detection of foreign exchange transactions by market traders.FX intervention, secrecy puzzle, market detection, nested logit

The stack resource protocol based on real time transactions

Current hard real time (HRT) kernels have their timely behaviour guaranteed at the cost of a rather restrictive use of the available resources. This makes current HRT scheduling techniques inadequate for use in a multimedia environment where one can profit by a better and more flexible use of the resources. It is shown that one can improve the flexibility and efficiency of real time kernels and a method is proposed for precise quality of service schedulability analysis of the stack resource protocol. This protocol is generalised by introducing real time transactions, which makes its use straightforward and efficient. Transactions can be refined to nested critical sections if the smallest estimation of blocking is desired. The method can be used for hard real time systems in general and for multimedia systems in particular