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John Regehr
Works at University of Utah
Attended University of Virginia
Lives in Salt Lake City
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John Regehr

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I have a program that implements a search using unix fork(). The search tree is maybe 30-40 forks deep. Without throttling, it's just a forkbomb that kills the host machine, so I'm in search of a good way to throttle it.

One way is, following each fork, for the parent to wait() for the child. This works fine and gives the invariant that there's almost always exactly one runnable process.

But what I want is the invariant that there are always N runnable processes, where N is the number of cores I have. For reasons I don't entirely understand, I'm having trouble getting this to work. Obvious tricks with a semaphore initialized to N don't work.

Anyone know the solution I'm looking for here?  Thanks!
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If you run the LLVM verifier, it aborts when opt-fuzz creates an invalid function, in which case the atexit handler won't bump the semaphore. I'm still trying to figure out a reasonable way to work around that problem. 

This generator is kind of stupid but in conjunction with another tool, has lead to the discovery of several nasty LLVM optimization bugs.
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John Regehr

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I learned most of what I know about static analysis from these notes. They're refreshingly direct and clear (unfortunately much of the other material on this topic isn't).
 
Our lecture notes on static program analysis are now online - with implementation and exercises.
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John Regehr

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IBM note explaining their opposition to removing trigraphs from C++. 

"The future is already here — it's just not very evenly distributed."

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4210.pdf
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It's not that programmers who face compiler bugs are 'so good', or that we suspect the compiler before our own code. It's that we're writing inherently intricate code, with lots of low-level interactions.

When something goes unexpectedly wrong, we investigate in depth, and find that expectations of the compiler don't square with what it's done.

In some cases, that means we eventually look at the generated assembly code, and see a mismatch with the source that doesn't arise from undefined or implementation-defined behavior in the relevant standard. E.g. Intel's compiler 'optimizing' a simple call to strrchr() to an inlined infinite loop. E.g. IBM's compiler emitting undefined linker references to symbols that the source code doesn't depend on.

In other cases, one compiler rejects code that others accept, and the standards say it should have too. E.g https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57743
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The results of the SIGPLAN survey on open access are in. There is a strong majority of respondents strongly in favor of getting rid of paywalls in the next two years. What will the ACM do? ‪#‎WhoOwnsYourResearch‬   http://janvitek.github.io/whoowns.html
There were 860 responses with 54% respondents being members of the ACM. Membership is higher in North America (75%) and lower in the rest of the world (49%). The majority of respondents are from Europe (53%) followed by the USA and Canada (37%). The geographic distribution of responses is shown ...
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Photographing Snowflakes in Freefall: A team of researchers at the University of Utah have developed a Multi-Angle Snowflake Camera. http://www.wired.com/2015/03/photographing-snowflakes-freefall/
A camera has been developed to show photographs of snowflakes in freefall.
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Have him in circles
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John Regehr

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Nothing is better than these recipes created by a recurrent neural network.
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+John Regehr Did you check out the RNN generated Linux code?
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Chandan Dalawat originally shared to Maths Articles:
 
The shortest paper ever ?

Bull. Amer. Math. Soc. 72 1966 1079.

http://www.ams.org/journals/bull/1966-72-06/S0002-9904-1966-11654-3/home.html
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+1 for CDC 6600 - Good times.
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From the "you just can't make this up"-department.
"Star Wars" fans are being warned away from several locations in Tunisia linked to the movies due to reported jihadist activity. Tataouine, which inspired the name of Luke Skywalker's home planet of Tatooine, has become a way-station fo...
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John Regehr

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Here's what I did today:
http://blog.regehr.org/archives/1229
Ever since learning that the space shuttle booster motors were manufactured and tested at ATK in Promontory Utah — not too far from where I live — I wanted to see one of the tests. I didn't manage to do that before the shuttle program was shut down, but today I got to see something better: a ...
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Just put a spray mister right over the slide entrance.
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Available
In case you have not heard through other social media outlets: Bit9 and I have parted ways, which leaves me looking for my next opportunity! Check out my resume . "Experienced software engineer and leader. Ported flagship Bit9 security product to Linux, imp...
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Have him in circles
935 people
awais Naseem's profile photo
licka kraus's profile photo
Benjamin Pierce's profile photo
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Paul Pluzhnikov's profile photo
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Dan Ciliske's profile photo
Education
  • University of Virginia
    CS, 1995 - 2001
  • Kansas State University
    CS and math, 1990 - 1995
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  • Monument Valley
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Employment
  • University of Utah
    prof, 2001 - present
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I've been here a number of times both without and with kids. It's a wonderful restaurant either way. The steak frites is completely fantastic as are several other items on the menu. I've loved most of the sides that I've tried. There's usually a nice soup. They're happy to let us split things when visiting with the kids. Their own beers are perfectly fine (though underpowered) but they have a decent selection of bottles also.
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