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Topic: Concurrency

	Concurrency (computer science) - Wikipedia, the free encyclopedia
		In computer science, concurrency is a property of systems which consist of computations that execute overlapped in time, and which may permit the sharing of common resources between those overlapped computations.
		Concurrent programming is usually considered to be more general than parallel programming because it can involve arbitrary and dynamic patterns of communication and interaction, whereas parallel systems generally have a predefined and well-structured communications pattern.
		Some concurrent systems implement a form of transparent concurrency, in which concurrent computational entities may compete for and share a single resource, but the complexities of this competition and sharing are shielded from the programmer.
	en.wikipedia.org /wiki/Concurrency_(computer_science) (523 words)

	Concurrency Utilities Overview
		The Concurrency Utilities include a high-performance, flexible thread pool; a framework for asynchronous execution of tasks; a host of collection classes optimized for concurrent access; synchronization utilities such as counting semaphores; atomic variables; locks; and condition variables.
		The implementations in the Concurrency Utilities were developed and peer-reviewed by concurrency and performance experts; these implementations are likely to be faster and more scalable than a typical implementation, even by a skilled developer.
		By using standardized, extensively tested concurrency building blocks, many potential sources of threading hazards such as deadlock, starvation, race conditions, or excessive context switching are eliminated.
	java.sun.com /j2se/1.5.0/docs/guide/concurrency/overview.html (618 words)

	Why Florida's Concurrency Principle For Controlling New Development By Regulating Road Construction Does Not - And ...
		The second fundamental flaw in the concurrency principle is that, in a free country, a community's future growth should not be - and probably cannot be - determined by the adequacy of its roadways at any given moment.
		The concurrency principle amounts to a state legislative fiat that Florida should not accept any more citizens unless it has enough roadways to provide both new and existing residents with a constant desired level of roadway mobility.
		The overall ineffectiveness of the road concurrency policy is proven by the fact that Florida's total population has continued to rise sharply - up 23.5 percent in the 1990s alone - in spite of obvious shortfalls in the state's roads and other infrastructures.
	www.anthonydowns.com /concurrency.htm (2562 words)

	CONCURRENCY
		The concurrency degree of a collaboration architecture ranges from 0 to R, where R is its replication degree.
		We refer to architectures with concurrency degree 0 and R as sequential and concurrent architectures, respectively, and the remaining architectures as semi-concurrent architectures (Figure 9.8).
		A concurrent architecture created using this approach does not necessarily offer the maximum possible concurrency, which would require an approach that identifies all portions of the application that could potentially execute concurrently and assigns each of these to a separate thread.
	www.cs.unc.edu /~dewan/abstracts/arch2/node10.html (733 words)

	Introduction to Concurrency Control
		Concurrency control deals with the issues involved with allowing multiple people simultaneous access to shared entities, be they objects, data records, or some other representation.
		To understand how to implement concurrency control within your system you must start by understanding the basics of collisions – you can either avoid them or detect and then resolve them.
		An important message of this article is that on modern software development projects that concurrency control and transactions are not simply the domain of databases, instead they are issues that are potentially pertinent to all of your architectural tiers.
	www.agiledata.org /essays/concurrencyControl.html (1786 words)

	Strategic Directions in Computing Research Concurrency Working Group Report
		Concurrency has emerged as a separate area of research in response to the intrinsic difficulties experienced by designers of concurrent systems in diverse fields within computer science.
		In contrast, truly concurrent models instead treat concurrency as a primitive notion; the behavior of systems is represented in terms of the causal relations among the events performed at different ``locations'' in a system.
		Linear-time models describe concurrent systems in terms of the sets of their possible (partial) runs while in branching-time models the points at which different computations diverge from one another is recorded.
	www.cs.sunysb.edu /~sas/sdcr/report/final/final.html (8703 words)

	Amazon.de: Concurrency. State Models and Java Programs.: English Books: Jeff Magee,Jeff Kramer (Site not responding. Last check: 2007-11-05)
		Concurrency is an area of software design that is vital in a wide range of applications where responsiveness are issues.
		In order to ensure a thorough understanding of concurrency, concepts, techniques and problems are presented in many forms, through informal descriptions and illustrative examples, abstractly in models, and concretely in Java.
		The concepts are well motivated, the intriguingly difficult theory of concurrency is well explained and the book is full of examples that show both theory and practice of Concurrency.
	www.amazon.de /Concurrency-State-Models-Java-Programs/dp/0471987107 (1086 words)

	Visual Studio Magazine - Database Design - Implement Optimistic Concurrency
		The two main types of concurrency checking are optimistic concurrency and pessimistic concurrency.
		Pessimistic concurrency ties locks in the database to user input: You lock the rows when you fetch them.
		Concurrency problems can occur when you update through the DataSet, but you can address them by using optimistic or pessimistic concurrency.
	www.ftponline.com /vsm/2003_08/magazine/columns/databasedesign (597 words)

	readings and resources
		Accounts of concurrency so often focus on isolated smart procedures operating on isolated dumb data that it is sometimes hard to see how the same ideas apply to object-oriented designs in general or Java in particular.
		However, the particular senses of ``concurrency control'' and ``transactions'' seen in accounts of database systems are more narrow and specialized, yet in some cases more extensively studied than those seen in the context of concurrent programming.
		The kinds of concurrency constructs found or easily emulated in Java are representative of those in most other concurrent OO languages.
	gee.cs.oswego.edu /dl/cpj/refs.html (3645 words)

	The Free Lunch Is Over: A Fundamental Turn Toward Concurrency in Software \| Lambda the Ultimate
		As a consequence he believes that concurrency will become a first class concern for more developers (including language designers) and language there will be a resurgence in interest in what he calls 'efficient languages'.
		I'm pretty sure the concurrency libraries in Java 5 were designed by Doug Lea.
		The authors of CTM and a few others have called shared-state concurrency "the wrong default" and proposed teaching simpler to reason about models to replace it, namely declarative concurrency and message-passing concurrency (the model of Erlang and E).
	lambda-the-ultimate.org /node/view/458 (5615 words)

	Concurrency - Haskell Prime - Trac (Site not responding. Last check: 2007-11-05)
		concurrent foreign calls are required to guarantee timely responsiveness of an interactive application in the presence of long-running foreign calls.
		Portability problems: if a programmer develops a concurrent application on a preemptive system, there is no guarantee that it will work as expected on a cooperative system, and the compiler/runtime can give no useful feedback.
		Concurrent calls allow the progress guarantee to be retained in the presence of a blocking foreign call.
	hackage.haskell.org /trac/haskell-prime/wiki/Concurrency (1745 words)

	Concurrency Control and Data Integrity
		In case of optimistic concurrency, clients are written to handle possible rollbacks of some of the parallel transactions.
		The main advantage of optimistic concurrency control method is faster response time, but on the downside you cannot be sure that the action will be performed until the lock has been accepted or rejected.
		For example, if there are many users, the probability of concurrent access is greater and so pessimistic concurrency control might be used, whereas if many users don't exist, concurrent access will be rarer so optimistic concurrency control might be better used.
	www.pramati.com /docstore/1230022/tref_concurrency.htm (1774 words)

	The Free Lunch Is Over: A Fundamental Turn Toward Concurrency in Software
		For technologists, the interesting thing is that concurrency is of the same order as OO both in the (expected) scale of the revolution and in the complexity and learning curve of the technology.
		Probably the greatest cost of concurrency is that concurrency really is hard: The programming model, meaning the model in the programmer’s head that he needs to reason reliably about his program, is much harder than it is for sequential control flow.
		But the concurrent programming model is learnable, particularly if we stick to message- and lock-based programming, and once grokked it isn’t that much harder than OO and hopefully can become just as natural.
	www.gotw.ca /publications/concurrency-ddj.htm (4802 words)

	Objects, Abstractions and Concurrency
		In a concurrent program, such member functions might be interleaved, exposing inconsistent states, and thereby destroying the encapsulation (and perhaps also the correctness) of the data abstraction.
		Our concurrency control model is defined in terms of visible state changes, rather than locking or exclusivity, to allow the compiler to optimize concurrency control.
		Concurrency control also interacts with derivation, and our concurrency model has been designed with this inheritance anomaly in mind, as discussed in Section 1.8.
	www-csag.ucsd.edu /papers/html/node4.html (1303 words)

	The Joys of Concurrent Programming > What is Concurrency? (Site not responding. Last check: 2007-11-05)
		Concurrency techniques are used to allow a computer program to do more work over the same time period or time interval.
		The concurrency of both processes is the natural form of the solution.
		Whether concurrency is used to make the software faster, handle larger loads, or simplify the programming solution, the main object is software improvement using concurrency to make the software better.
	www.informit.com /articles/article.asp?p=30413 (1592 words)

	Applying WebLogic Server Optimistic Concurrency
		The option can allow optimistic concurrency to work at a finer level of granularity than a complete entity, but this may not be an advantage: it is often desirable from the data integrity perspective that changing one field of an entity instance should be incompatible with changes to any other field of that instance.
		Whilst the use of database or exclusive concurrency strategies can ensure that individual JTA transactions are serialisable, it does not ensure that what the user sees on the screen is correct when the changes are written to the database.
		The new optimistic concurrency strategy provides the same degree of data integrity guarantees as the database concurrency strategy but, because it is not scoped within a JTA transaction, does not have its shortcomings.
	dev2dev.bea.com /pub/a/2003/06/Optimistic_Concurrency.html (3590 words)

	The CONCURRENCY Mailing List (Site not responding. Last check: 2007-11-05)
		CONCURRENCY is a moderated email forum focusing on concurrent process theory, especially operational and abstract semantics, specification, and verification of: concurrent, distributed, reactive, real-time and hybrid systems.
		The CONCURRENCY forum was founded by Albert Meyer (MIT) and has been maintained by Frits Vaandrager until the end of 1997.
		A hypermail archive of the CONCURRENCY mailing list, containing the messages sent in the years between 1988 and 2002, is maintained by Martin Leucker at the RWTH Aachen.
	homepages.cwi.nl /~bertl/concurrency (262 words)

	The World Wide Web Virtual Library: Concurrent Systems
		Concurrent Systems Architecture Group, Department of Computer Science, University of Illinois at Urbana-Champaign, USA.
		Concurrent and Distributed Systems research group at University of St. Andrews, Scotland.
		CWB-NC (The Concurrency Workbench of North Carolina), which includes a LOTOS interface, diagnostic infomation, etc. Note: The CWB and CWB-NC have a common ancestor, but are each under separate development.
	www.comlab.ox.ac.uk /archive/concurrent.html (969 words)

	Amazon.com: Java Concurrency in Practice: Books: Brian Goetz,Tim Peierls,Joshua Bloch,Joseph Bowbeer,David Holmes,Doug ... (Site not responding. Last check: 2007-11-05)
		Java SE 5 and 6 are a huge step forward for the development of concurrent applications, with improvements to the Java Virtual Machine to support high-performance, highly scalable concurrent classes and a rich set of new concurrency building blocks.
		He specializes in synchronization and concurrency and was a member of the JSR-166 expert group that developed the new concurrency utilities.
		Concurrency, in the form of threads, has been present in the Java language from its beginning, and this book is all about concurrency in the current and future versions of Java with an emphasis on writing practical code.
	www.amazon.com /Java-Concurrency-Practice-Brian-Goetz/dp/0321349601 (3238 words)

	Dr. Dobb's \| Object Concurrency Control 101 \| June 29, 2001 (Site not responding. Last check: 2007-11-05)
		Pessimistic concurrency control locks the source for the entire time that a copy of it exists, not allowing other copies to exist until the copy with the lock has finished its transaction.
		This is a brute force approach to concurrency that is applicable for small-scale systems or systems where concurrent access is very rare: Pessimistic locking doesn't scale well because it blocks simultaneous access to common resources.
		Your object concurrency control strategy should be implemented in a common application framework or reusable component that everyone uses in their code.
	www.ddj.com /dept/architect/184414697?cid=Ambysoft (1925 words)

	K. Scott Allen : Concurrency
		Like Jeff Atwood, I don’t think concurrency is an area the typical application developer is ever going to deal with.
		When Comega first appeared I thought the next version of C# would be taking a turn towards new concurrency abstractions, but I see no mention of these in the C# 3.0 specification.
		Some of the platforms I write for won't let you make any kind of socket connection from the main UI thread so everything has to be threaded and feed it's data to the main UI thread when it's done or when it retrieves something.
	odetocode.com /Blogs/scott/archive/2005/09/19/2261.aspx (355 words)

	Concurrency (Site not responding. Last check: 2007-11-05)
		For the right kind of code, it makes life very easy for the programmer, as you don't have to think too much about concurrency issues, and you don't have to deal with threads.
		The downside for J2ME is that we don't have the equivalent of select, so we'd have to do the system with threads, which would probably be costly in terms of the resources required to set it up.
		Conceptually, I think this is a cleaner way of doing threads, compared with 'sharing everything and using mutexes', and it's a little closer to how Erlang handles concurrency, which is very nice indeed.
	journal.dedasys.com /articles/2006/06/24/concurrency (420 words)

	Server clinic: Concurrency for grown-ups
		Concurrency labels situations where more than one "application" is running at a time.
		Events are a distinct concurrency concept useful for managing I/O and related multi-tasking responsibilities.
		Remember that concurrency has both a forward- and backward-facing aspect: the "user view" or "programming model" controls the functionality of how you interact with an application, while the "back end" manages assignment of tasks to hardware.
	www-106.ibm.com /developerworks/library/l-sc5.html (1642 words)

	Synopsis on concurrency (Site not responding. Last check: 2007-11-05)
		Under the heading of ``Concurrency'' goes the analysis of the problems that in a multiprogramming environment may occur when processes share resources like the content of a shared memory area, files, devices.
		In general, these are all problems due to lack of proper synchronization in the access to the shared resources, which may cause data corruption or evil situations, known as deadlocks, in which processes are stalled waiting to access a shared resource, and never being allowed to.
		A general treatment of concurrency problems starts with the definition of the concept of ``critical section'' of a program: it's simply a code fragment in which a shared resource is accessed, and encapsulation in the source of these code fragments is of vital importance for the fruitful use of the above mentioned tools.
	www.cim.mcgill.ca /~franco/OpSys-304-427/lecture-notes/node29.html (433 words)

	Java Concurrency in Practice - $39.99 (Site not responding. Last check: 2007-11-05)
		One of the challenges of developing concurrent programs in Java is the mismatch between the concurrency features offered by the platform and how developers need to think about concurrency in their programs.
		Java 5.0 is a huge step forward for the development of concurrent applications in Java, providing new higher-level components and additional low-level mechanisms that make it easier for novices and experts alike to build concurrent applications.
		The authors are the primary members of the JCP Expert Group that created these facilities; in addition to describing their behavior and features, we present the underlying design patterns and anticipated usage scenarios that motivated their inclusion in the platform libraries.
	www.awprofessional.com /title/0321349601 (1828 words)

	The Java Community Process(SM) Program - JSRs: Java Specification Requests - detail JSR# 166
		As a result, application programmers are often forced to implement their own higher level concurrency facilities.
		The concurrency facilities written by application programmers are often incorrect or inefficient.
		Offering a standard set of concurrency utilities will ease the task of writing a wide variety of multithreaded applications and generally improve the quality of the applications that use them.
	jcp.org /en/jsr/detail?id=166 (624 words)

	Concurrency in JDK 5.0
		JDK 5.0 added major new support for developing concurrent applications, including JVM changes, new low-level synchronization utilities, and higher-level, thread-safe, high-performance concurrency classes such as thread pools, concurrent collections, semaphores, latches, and barriers.
		While this tutorial is aimed at a wide range of levels, it is assumed that readers have a basic understanding of threads, concurrency, and the concurrency primitives provided by the Java language, particularly the semantics and correct use of synchronization.
		Beginning readers may wish to first consult the "Introduction to Java Threads" tutorial, or read the concurrency chapter of a general purpose introductory text on the Java language.
	www.ibm.com /developerworks/edu/j-dw-java-concur-i.html?ca=drs-j4904 (182 words)

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