Facing up to parallelism

Multicore means today's HPC is tomorrow's general purpose

Boost IT visibility and business value

There is, of course, a great deal known about parallel programming and there are already two promising programming approaches that Smith is pursing. One is functional programming and the other is atomic memory transactions. Neither is a complete answer in itself, of course. Functional programming, for example, does not allow mutable states to exist, while atomic memory transactions implement dependence awkwardly. The use of such technologies in mainstream computing is new ground and he acknowledged that atomic memory transaction technology already has critics claiming it is doomed to be too slow. He also pointed out that this was still to be shown as a permanent condition.

He did highlight two functional programming languages, Sisal and NESL, for specific mention, however. "Critics say that functional languages are inefficient, but these two are excellent counter-examples. On Cray systems they could run as fast as Fortran."

One of the issues that confronts programmers moving into the parallel processing world is the role of transactions in the management of invariants.

"Invariants are a program's conservation laws," he observed. "And there are rules of data structure, or state, integrity that need to be observed." These rules were developed in the paper Verifying properties of parallel programs: An axiomatic approach by Susan Owicki and David Gries, which sets out the following law:

If statements p and q preserve the invariant I and they do not "interfere", their parallel composition { p|| q} also preserves I.

Transactions then play their part as set out by Leslie Lamport and Fred Schneider in their paper The Hoare Logic of CSP, And All That:

If p and q are performed atomically, i.e. as transactions, then they will not interfere.

As Smith observed: "Although operations seldom commute with respect to state, transactions give us commutativity with respect to the invariant, and it would be nice if the invariants were available to the compiler if programmers can provide them readily."

For Microsoft programmers he pointed to the new C# and Visual Basic enhancements to be found with LINQ (Language Integrated Query) project, a set of extensions to the .NET Framework that add such capabilities as language-integrated query, set, and transform operations and can operate on data in memory or in an external database.

His view is that, for the immediate future, all the major styles of parallel programming should be supported. These include both functional and transactional styles, data parallel and task parallel, message passing and shared memory, declarative and imperative, and implicit and explicit styles.

"To cover all these will require more than one language, but then we use multiple languages today as it is. What is important is that the parallelism and locality are exposed to the compiler, so that the compiler can adapt them for the target system."

Here, he suggested that the ability to work with heterogeneous processors in any infrastructure would be an important capability. "We will need independence from the idiosyncrasies of the machine."

He also pointed delegates to the language interoperability available with .NET as a help. This would help provide automatic parallelisation, which he said many have already suggested is demonstrated failure. "What failed is parallelism discovery, particularly in-the-large. There is now a need to package parallelism, which means not worrying about how many cores are available at any one time or about whether you need to recompile the application for a different number of cores."

When it comes to debugging parallel applications, Smith suggested that setting conditional data breakpoints and ad-hoc data perusal are likely to be two important techniques for developers to learn. The former is a technique which stops the application if an invariant fails to be true, while the latter is a form of data mining application. Application tuning will also be important, particularly in identifying where there is insufficient parallelism available.

As a call-to-arms in facing up to what he sees as inevitable, he told delegates: "We have to rethink the basics of computing, but thanks to HPC we have a good starting point. It does mean, however, that many applications will have to be re-modeled and re-engineered from the strategy downwards." ®

Build a business case: developing custom apps

More from The Register

next story
KDE releases ice-cream coloured Plasma 5 just in time for summer
Melty but refreshing - popular rival to Mint's Cinnamon's still a work in progress
Leaked Windows Phone 8.1 Update specs tease details of Nokia's next mobes
New screen sizes, dual SIMs, voice over LTE, and more
Mozilla keeps its Beard, hopes anti-gay marriage troubles are now over
Plenty on new CEO's todo list – starting with Firefox's slipping grasp
Apple: We'll unleash OS X Yosemite beta on the MASSES on 24 July
Starting today, regular fanbois will be guinea pigs, it tells Reg
Another day, another Firefox: Version 31 is upon us ALREADY
Web devs, Mozilla really wants you to like this one
Secure microkernel that uses maths to be 'bug free' goes open source
Hacker-repelling, drone-protecting code will soon be yours to tweak as you see fit
Cloudy CoreOS Linux distro declares itself production-ready
Lightweight, container-happy Linux gets first Stable release
prev story


Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
The Essential Guide to IT Transformation
ServiceNow discusses three IT transformations that can help CIO's automate IT services to transform IT and the enterprise.
Maximize storage efficiency across the enterprise
The HP StoreOnce backup solution offers highly flexible, centrally managed, and highly efficient data protection for any enterprise.