The Art of Multiprocessor Programming

Stephen J. Hartley Oxford University Press, New York, 1998, 260 pp. ISBN 0-19-511315-2, $45.00 Concurrent Programming  is a thorough treatment of Java multi-threaded programming for both a stand-alone and distributed environment. Designed mostly for students in concurrent or parallel programming classes, the text is also an excellent reference for the practicing professional developing multi-threaded programs or applets. Hartley first provides a complete explanation of the features of Java necessary to write concurrent programs, including topics such as exception handling, interfaces, and packages. He then gives the reader a solid background to write multi-threaded programs and also presents the problems introduced when writing concurrent programs—namely race conditions, mutual exclusion, and deadlock. Hartley also provides several software solutions that do not require the use of common process and thread mechanisms. Once the groundwork is laid for writing concurrent programs, Hartley then takes a different approach than most Java references. Rather than presenting how Java handles mutual exclusion with the  synchronized  keyword (although it is covered later), he first looks at semaphore-based solutions to classic concurrent problems such as bounded-buffer, readers-writers, and the dining philosophers. Hartley also uses the same approach to develop Java classes for monitors and message passing. This unique approach to introducing concurrency allows the readers to both understand how Java threads are synchronized and how the basic synchronization mechanism can be used to construct more abstract tools such as semaphores. If there is a shortcoming with the text it is with the lack of sufficient coverage of remote method invocation (RMI), although there is a section covering RMI. This is quite understandable as RMI is a fairly recent phenomenon with the Java community. Also, the classes that Hartley provides could easily implement RMI rather than sockets to handle communication. The strengths of the book include its ease in reading, several examples at the end of chapters, a package similar to Xtango that provides algorithm animation, and a supportive web site by the author (see  www.mcs.drexel.edu/~shartley/ConcProgJava/index.html ) including compressed source code. As Java becomes more dominant on the server side of multi-tier applications, writing thread-safe concurrent applications becomes even more important.  Concurrent Programming  is a strong step towards teaching students and professionals such skills. Greg Gagne, Westminster College of Salt Lake City Salt Lake City, Utah

Distributed Computing: Fundamentals, Simulations and Advanced Topics

The advent of multicore processors has renewed interest in the idea of incorporating transactions into the programming model used to write parallel programs. This approach, known as transactional memory, offers an alternative, and hopefully better, way to coordinate concurrent threads. The ACI (atomicity, consistency, isolation) properties of transactions provide a foundation to ensure that concurrent reads and writes of shared data do not produce inconsistent or incorrect results. At a higher level, a computation wrapped in a transaction executes atomically - either it completes successfully and commits its result in its entirety or it aborts. In addition, isolation ensures the transaction produces the same result as if no other transactions were executing concurrently. Although transactions are not a parallel programming panacea, they shift much of the burden of synchronizing and coordinating parallel computations from a programmer to a compiler, to a language runtime system, or to hardware. The challenge for the system implementers is to build an efficient transactional memory infrastructure. This book presents an overview of the state of the art in the design and implementation of transactional memory systems, as of early spring 2010. Table of Contents: Introduction / Basic Transactions / Building on Basic Transactions / Software Transactional Memory / Hardware-Supported Transactional Memory / Conclusions

Transactional Memory, 2nd Edition

Most high-performance software transactional memories (STM) use optimistic invisible reads. Consequently, a transaction might have an inconsistent view of the objects it accesses unless the consistency of the view is validated whenever the view changes. Although all STMs usually detect inconsistencies at commit time, a transaction might never reach this point because an inconsistent view can provoke arbitrary behavior in the application (e.g., enter an infinite loop). In this paper, we formally introduce a lazy snapshot algorithm that verifies at each object access that the view observed by a transaction is consistent. Validating previously accessed objects is not necessary for that, however, it can be used on-demand to prolong the view's validity. We demonstrate both formally and by measurements that the performance of our approach is quite competitive by comparing other STMs with an STM that uses our algorithm.

https://doc.rero.ch/record/18139/files/Riegel_Torvald_-_A_Lazy_Snapshot_Algorithm_with_Eager_Validation_20100430.pdf

A Lazy Snapshot Algorithm with Eager Validation

Distributed Computing Through Combinatorial Topology describes techniques for analyzing distributed algorithms based on award winning combinatorial topology research. The authors present a solid theoretical foundation relevant to many real systems reliant on parallelism with unpredictable delays, such as multicore microprocessors, wireless networks, distributed systems, and Internet protocols. Today, a new student or researcher must assemble a collection of scattered conference publications, which are typically terse and commonly use different notations and terminologies. This book provides a self-contained explanation of the mathematics to readers with computer science backgrounds, as well as explaining computer science concepts to readers with backgrounds in applied mathematics. The first section presents mathematical notions and models, including message passing and shared-memory systems, failures, and timing models. The next section presents core concepts in two chapters each: first, proving a simple result that lends itself to examples and pictures that will build up readers' intuition; then generalizing the concept to prove a more sophisticated result. The overall result weaves together and develops the basic concepts of the field, presenting them in a gradual and intuitively appealing way. The book's final section discusses advanced topics typically found in a graduate-level course for those who wish to explore further. Gathers knowledge otherwise spread across research and conference papers using consistent notations and a standard approach to facilitate understandingPresents unique insights applicable to multiple computing fields, including multicore microprocessors, wireless networks, distributed systems, and Internet protocols Synthesizes and distills material into a simple, unified presentation with examples, illustrations, and exercises

Distributed Computing Through Combinatorial Topology

Virtual world consistency: A condition for STM systems (with a versatile protocol with invisible read operations)

This BA presents a general consistency condition for software transactionnal memories.

Brief announcement: virtual world consistency: a new condition for STM systems

An atomic snapshot object is an object that can be concurrently accessed by asynchronous processes prone to crash. It is made of m components (base atomic registers) and is defined by two operations: an update operation that allows a process to atomically assign a new value to a component and a snapshot operation that atomically reads and returns the values of all the components. To cope with the net effect of concurrency, asynchrony and failures, the algorithm implementing the update operation has to help concurrent snapshot operations so that they always terminate.

This paper is on partial snapshot objects. Such an object provides a snapshot operation that can take any subset of the components as input parameter, and atomically reads and returns the values of this subset of components. The paper has two contributions. The first is the introduction of two properties for partial snapshot object algorithms, called help-locality and freshness. Help-locality requires that an update operation helps only the concurrent partial snapshot operations that read the component it writes. When an update of a component r helps a partial snapshot, freshness requires that the update provides the partial snapshot with a value of the component r that is at least as recent as the value it writes into that component. (No snapshot algorithm proposed so far satisfies these properties.) The second contribution consists of an update and a partial snapshot algorithms that are wait-free, linearizable and satisfy the previous efficiency properties. Interestingly, the principle that underlies the proposed algorithms is different from the one used so far, namely, it is based on the "write first, and help later" strategy. An improvement of the previous algorithms is also presented. Based on LL/SC atomic registers (instead of read/write registers) this improvement decreases the number of base registers from O(n2) to O(n). This shows an interesting tradeoff relating the synchronization power of the base operations and the number of base atomic registers when using the "write first, and help later" strategy.

/pdf/help-when-needed-but-no-more-efficient-read-write-partial-28yrgay1wu.pdf

Help when needed, but no more: efficient read/write partial snapshot

The aim of a software transactional memory (STM) system is to facilitate the delicate problem of low-level concurrency management, i.e. the design of programs made up of processes/threads that concurrently access shared objects. To that end, a STM system allows a programmer to write transactions accessing shared objects, without having to take care of the fact that these objects are concurrently accessed: the programmer is discharged from the delicate problem of concurrency management. Given a transaction, the STM system commits or aborts it. Ideally, it has to be efficient (this is measured by the number of transactions committed per time unit), while ensuring that as few transactions as possible are aborted. From a safety point of view (the one addressed in this paper), a STM system has to ensure that, whatever its fate (commit or abort), each transaction always operates on a consistent state.

STM systems have recently received a lot of attention. Among the proposed solutions, lock-based systems and clock-based systems have been particularly investigated. Their design is mainly efficiency-oriented, the properties they satisfy are not always clearly stated, and few of them are formally proved. This paper presents a lock-based STM system designed from simple basic principles. Its main features are the following: it (1) uses visible reads, (2) does not require the shared memory to manage several versions of each object, (3) uses neither timestamps, nor version numbers, (4) satisfies the opacity safety property, (5) aborts a transaction only when it conflicts with some other live transaction (progressiveness property), (6) never aborts a write only transaction, (7) employs only bounded control variables, (8) has no centralized contention point, and (9) is formally proved correct.

A Lock-Based STM Protocol That Satisfies Opacity and Progressiveness

https://hal.inria.fr/inria-00339292/document

Damien Imbs

Papers

Virtual world consistency: A condition for STM systems (with a versatile protocol with invisible read operations)

Brief announcement: virtual world consistency: a new condition for STM systems

Help when needed, but no more: efficient read/write partial snapshot

A Lock-Based STM Protocol That Satisfies Opacity and Progressiveness

Help when needed, but no more: Efficient read/write partial snapshot