SPLASH 2011: David Ungar - Self, ManyCore, and Embracing Non-Determinism
- Posted: Nov 17, 2011 at 6:00 AM
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David Ungar is a visionary computer scientist and engineer currently working at IBM Research. He is the co-creator of the object-oriented Self programming language, which is a language influenced by SmallTalk and one that has influenced many other languages, not the least of which is today's darling of the web, JavaScript. Self has also helped move virtual machine evolution forward (interestingly, Google's Lars Bak (V8) was at one point David's employer).
It's an honor to finally have David on Channel 9, to get to ask him about what inspired the Self project, what he's up to today, and what he thinks are currently the biggest problems in computing. Of course, David has lately been busy working on the concurrency problem—how does one reasonably program 1,000 core machines, anyway? Here's an excerpt from the description of his excellent SPLASH 2011 talk on how to think about and program ManyCore (I was there. Dave is (again) way ahead of his time for sure, and he's working with a great cast including Sam Adams, Doug Kimelman, and Mark Wegman...):
In our Renaissance project at IBM, Brussels, and Portland State, we are investigating what we call "anti-lock," "race-and-repair," or "end-to-end nondeterministic" computing. As part of this effort, we have built a Smalltalk system that runs on the 64-core Tilera chip, and have experimented with dynamic languages atop this system. When we give up synchronization, we of necessity give up determinism. There seems to be a fundamental tradeoff between determinism and performance, just as there once seemed to be a tradeoff between static checking and performance.
The obstacle we shall have to overcome, if we are to successfully program manycore systems, is our cherished assumption that we write programs that always get the exactly right answers. This assumption is deeply embedded in how we think about programming. The folks who build web search engines already understand, but for the rest of us, to quote Firesign Theatre: Everything You Know Is Wrong!
Recently, Channel 9 was invited to attend the great SPLASH conference. What is SPLASH? Systems, Programming, Languages and Applications: Software for Humanity. A big thanks to the SPLASH event organizers for inviting me and my camera to engage some key computer scientists and engineers in geeky, fun conversation! SPLASH is a great event! I learned a ton and met many amazing computer scientists and students.
SPLASH is an annual conference that embraces all aspects of software construction and delivery, and that joins all factions of programming technologies. Since 2010 SPLASH is the umbrella for OOPSLA and Onward! [source=splashcon.org]
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This is fantastic.
A fascinating and insightful interview!
Post updated on Nov 18th, 2011, with:
A great interview with a computer science pioneer and a visionary of the future of computing!
Notable points:
- David's pioneering work in the Self programming language influenced profoundly computer science and software technology (Self's adaptive optimization [1:37], object prototyping [2:58], cartoon animation GUI [3:46])
- the future of computer architecture [5:52]
- the challenges of parallel programming [7:42]
- researching new data structures & algorithms that deal with imperfect computations [12:20]
- what apps would take advantage of a PC with 1000 cores? [13:28]
- building systems that unleash creativity in people, matters the most to David [15:45]
My annotations on the full video follow:
- [0:20] Q: what's David's vision behind the Self programming language?
- [0:23] David's preocupation was in bridging the gap BETWEEN how people think AND computer programming thinking
- [0:54] Self was born by removing features from Smalltalk
- [1:12] surprizing discovery: language got more powerful by removing features
- [1:37] reference to pioneering work in Self's adaptive optimization
- [2:38] JVM users benefit from the early optimization ideas in Self
- [2:58] Javascript benefits from the prototype object orientation pioneered in Self
- [3:03] prototype model better matches how people think
- [3:12] reference to a book on experiments on how people think
- [3:22] prototype model is a more effective way to deal with objects in class-based model
- [3:46] application of cartoon animation to user interfaces
- [5:15] the problem on parallel programming, not solvable by today's approaches
- [5:52] reference to an IBM project on the future of computer architecture with cheap chips of hundered or thousand cores
- [7:42] reference to Amdahl law, of serial limitations put by parallel-serial processing
- [8:14] the challenge of removing the 10% serialization
- [8:24] synchronization issue in serialization (that doesn't scale)
- [8:50] the value in abandoning serialization
- [9:43] the fundamental tradeoff between correctness and performance
- [10:42] reference to David's report on a spreadsheet application and a data structure
- [11:58] mitiation strategies
- [12:20] reference to a new research area of data structures & algorithms to allow imperfections and go back and mitigate them
- [13:28] what apps would take advantage of a PC with 1000 cores? Business analytics, [14:31] smarter planet apps, natural language understanding, IBM Watson, [15:34] associative search (finding info on PC the way you think)
- [15:45] what is the biggest problem that matter the most to David?
- [16:08] David cares about building systems that unleash creativity in people
- [18:09] David's take on SPLASH: "mobile intelectual brigadoon"
- [19:30] reference to IBM's culture on looking into the future
- [20:10] the tools David is using
- [20:35] ref to a free Virtual Machine running on 60 cores
Quite a delightful fellow, he would be a great mentor for many these days. I wonder if he would like my conceptual solution for parallelizing sequential computation.
http://toxprox.tumblr.com/post/184172056/the-many-core-answer-relativistic-computation
It uses pipelining in a vectorized form relative to other pipelines in the system, and is a just-above abstraction above instruction level parallelism. There's a diagram for people to enjoy too
What do people think?
Thanks a lot for the great interview; is David's talk on video? Or is there presentation materials I can get a hold of?
10:30 talks about the exact problem I am dealing with right now. We have a hashtable datastructure using locking for synchronization. It has been giving us, alternatingly, performance problems (high CPU due to spinwait not using YieldProcessor, but an older x86 only assembly rep nop call), and duplicate key problems. There is another race condition happening that I can't seem to prevent, where the probable cause is that lookups in the hashtable is not a critical section and if it was then we'd reduce performance and introduce deadlocks. Some thread A wants to insert a record into the cache, A checks for an existing entry, finds none, then sleeps. Thread B then wants to insert the record in the cache, does the lookup for an existing entry, finds none, but continues and inserts the record. Thread A wakes up and thinks it is fine to insert the record, since it just checked, now you attempt to insert a duplicate. There are many other problems to mitigate as well. It becomes so complicated that you can't duplicate bugs when they occur.
In my research I've found this paper: Split-Ordered Lists: Lock-Free Extensible Hash Tables and related papers, such as Resizable, scalable, concurrent hash tables. I'm interested in hearing anything anyone has to say about those papers and if anyone has implemented them, I think I will have to try it, as our product is being scaled up so much that the existing locking based hashtable simply cannot work reliably or fast enough anymore.
@HeavensRevenge: Checking it out. I found another paper called "Resizable, Scalable, Concurrent Hash Tables via Relativistic Programming" ... it's new to me.
@Richard.Hein: Thats a damn good paper, I had no idea my idea/term is spreading and is helping to make research progress in ways I hadn't known
Thanks for linking that paper, I'd definitely suggest that sort of solution for your hash table not by bias but by such impressive results they got.
Good luck with coding a prototype for your product.
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