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Archive for November, 2009

The ISO C++ committee met in Santa Cruz, CA, USA on October 19-24. You can find the minutes here, which include the votes at the whole-group sessions but not the details of the breakout technical sessions where we spend most of the week.

The good news is that there’s little new technical news. We did a lot of work during the week, but it was mostly working on refining the standard, deciding integration questions of how two language features should work together in cases not clearly described, fixing bugs, and answering national body comments on our first public draft last fall (those are now nearly all answered). We expect to produce another public draft at our next meeting in March.

We did vote in one small feature that I and Lawrence Crowl in particular had been working on: a simple async() facility to launch asynchronous work easily without messing with packaged_tasks and raw threads. Here’s a sample use, also demonstrating a simple use of the futures library and a lambda function for kicks:

  future f = std::async( []{ OtherWork(); } );

  //... do our own work concurrently with OtherWork ...

  OkayNowWeNeedTheResult( f.get() );  // blocks if necessary until f is ready

If you’ve been following the futures library, you’ll notice a name change above: We also renamed unique_future<T> to just plain future<T> as part of recasting the futures wording to make it clearer and more consistent. That’s an example of the kind of cleanup work being done.

Near the end of the meeting, we also discussed deprecating export (as I reported earlier) and exception specifications other than throw()-nothing. There seemed to be significant support for deprecating both, and so we’ll probably see a concrete proposal at our next meeting.

In sad news, the convener (chair) of the committee for the past year, P.J. Plauger, stepped down at the end of the meeting. After I had been the convener for two three-year terms from 2002 to 2008, I decided it was time for someone else to have a go and so Plauger replaced me a year ago. He has done a really great job over the past year and his contributions in that role will be missed, but we won’t lose his services entirely as he remains an active participant in the committee. I will probably volunteer again to replace him.

That’s pretty much it. The next meeting of the ISO C++ standards committee is in March:

(Edited to fix “2009” in the title and add a link to the Pittsburgh meeting invitation.)

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This month’s Effective Concurrency column, Prefer structured lifetimes – local, nested, bounded, deterministic, is now live on DDJ’s website.

From the article:

Where possible, prefer structured lifetimes: ones that are local, nested, bounded, and deterministic. This is true no matter what kind of lifetime we’re considering, including object lifetimes, thread or task lifetimes, lock lifetimes, or any other kind. …

I hope you enjoy it. Finally, here are links to previous Effective Concurrency columns:

The Pillars of Concurrency (Aug 2007)

How Much Scalability Do You Have or Need? (Sep 2007)

Use Critical Sections (Preferably Locks) to Eliminate Races (Oct 2007)

Apply Critical Sections Consistently (Nov 2007)

Avoid Calling Unknown Code While Inside a Critical Section (Dec 2007)

Use Lock Hierarchies to Avoid Deadlock (Jan 2008)

Break Amdahl’s Law! (Feb 2008)

Going Superlinear (Mar 2008)

Super Linearity and the Bigger Machine (Apr 2008)

Interrupt Politely (May 2008)

Maximize Locality, Minimize Contention (Jun 2008)

Choose Concurrency-Friendly Data Structures (Jul 2008)

The Many Faces of Deadlock (Aug 2008)

Lock-Free Code: A False Sense of Security (Sep 2008)

Writing Lock-Free Code: A Corrected Queue (Oct 2008)

Writing a Generalized Concurrent Queue (Nov 2008)

Understanding Parallel Performance (Dec 2008)

Measuring Parallel Performance: Optimizing a Concurrent Queue (Jan 2009)

volatile vs. volatile (Feb 2009)

Sharing Is the Root of All Contention (Mar 2009)

Use Threads Correctly = Isolation + Asynchronous Messages (Apr 2009)

Use Thread Pools Correctly: Keep Tasks Short and Nonblocking (Apr 2009)

Eliminate False Sharing (May 2009)

Break Up and Interleave Work to Keep Threads Responsive (Jun 2009)

The Power of “In Progress” (Jul 2009)

Design for Manycore Systems (Aug 2009)

Avoid Exposing Concurrency – Hide It Inside Synchronous Methods (Oct 2009)

Prefer structured lifetimes – local, nested, bounded, deterministic (Nov 2009)

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I mentioned yesterday that I’ll be involved in two sessions at PDC09, including a parallel patterns tutorial. I know many of you are interested in concurrency in general and on Microsoft platforms in particular, so I thought I’d share this more complete list of concurrency-related sessions at PDC, put together by my colleague Stephen Toub.

Overview:

Native code in Visual Studio 2010:

Managed code in Visual Studio 2010:

HPC Server:

Research and Incubation:

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For those of you coming to PDC’09 in Los Angeles a couple of weeks from now, I’ll be there for a few hours on Monday and Wednesday participating in two events:

See you at PDC!

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