Ruby Threads and the Global Interpreter Lock in C

https://www.omniref.com/ruby/2.2.0.preview1/files/thread_pthread.h#annotation=4057266&line=38

by montanalow • 12 years ago

56 25 12 years ago

towski• 12 years ago

The only question I have is, how much work is it to create a C based ruby without a global interpreter lock.

montanalow2• 12 years ago

Matz mentioned off hand at the last Ruby Conf that Nobu has been experimenting without the GIL. It's scary because running code without the GIL will expose a lot of existing concurrency bugs that have been safely hidden thus far. A lot of code works fine with the GIL, since it prevents the full parallelism that would exercise all possible race conditions, so it's unlikely they'd remove it in anything other than a major release, i.e. Ruby 3.0

philwelch• 12 years ago

He also tweeted this awhile ago: https://twitter.com/yukihiro_matz/status/495219763883163648

"My vague plan for Ruby GIL is 1) add more abstract concurrency e.g. actors 2) add warning when using threads directly 3) then remove GIL"

masklinn• 12 years ago

An other issue, the one CPython has hit repeatedly when trying to remove the GIL — and the big sticking point for the core team in general — is that single-threaded performances of a naive interpreter suffer a lot when splitting the GIL: instead of a single lock which is taken and released relatively rarely, the interpreter has to juggle with many small locks which it has to acquire and release much more often. When David Beazley looked back on the GIL-less patch for CPython 1.4[0] he measured performance hits of 4x~7x.

Though in the case of CPython most of the cost comes from the refcounting. MRI is not refcounted so the performance hit of finer locking would probably be lower.

[0] http://dabeaz.blogspot.be/2011/08/inside-look-at-gil-removal...

dfox• 12 years ago

Creating MRI/CPython/Perl5-style VM without GIL is not much harder than creating the same thing with GIL. But the problem is that converting existing implementation to not use GIL is comparable amount of work.

sandstrom• 12 years ago

It mentions Rubinius briefly (it doesn't have a GIL).

Slightly of topic, but can anyone with better knowledge then myself of ruby implementations and internals explain why it hasn't caught much of a following (what it seems anyway, I may be wrong here).

To me it seems like a pretty good idea to implement Ruby mostly in Ruby, since it makes it easier to get contributions (especially to less performance-sensitive parts of the language, e.g. parts of the standard lib).

montanalow2• 12 years ago

Rubinius is neat, but for me personally (and I think most of the community) it's performance. Writing C enables optimizations by hand that still yield very significant performance gains over the best of what any other high level language (java, c++, ruby) can muster. I don't want to write C, but I'm glad someone else does so I get the benefits when I write Ruby.

FranzVonSuppe• 12 years ago

I don't understand how you can say Java, C++, and Ruby in the same breath. They are not at all alike. Also what optimizations are available to C which are not in C++? C++ is (almost) a strict superset of C.

cremno• 12 years ago

CRuby's standard library is partially written in Ruby.

https://github.com/ruby/ruby/tree/trunk/lib

Rubinius' one (called RubySL) also includes some rewrites of standard libraries, that were originally written in C. And as you may know, Rubinius itself is just Ruby code to some extent.

https://github.com/rubysl

mruby has some Ruby code, too. Even some parts of the core language are written in it.

https://github.com/mruby/mruby/tree/master/mrblib

Argorak2• 12 years ago

Rubinius has been traditionally lagging behind in features (e.g. for a long time didn't implement 1.9 string encoding properly) and wasn't necessarily _that_ much faster.

Also, people that do want to work at the core of a language usually have knowledge of multiple and don't mind using C or any other implementation language.

Ruby stdlib is mostly written in Ruby, btw.

Still, with Rubinius 3.0 coming up, I'm very interested what is coming there.

pmontra• 12 years ago

This 3 parts series from 2013 explains in details how the GIL works http://www.jstorimer.com/blogs/workingwithcode/8085491-nobod...

Disclaimer: it's linked in the omniref.com page too.

hardwaresofton2• 12 years ago

Did anyone notice a popup box asking you if you "didn't find what you were looking for"?

it appeared almost automatically after I moved my mouse to close the tab... Are they doing some mouse tracking and looking for rapid movement off screen (to the top of the page)?

If so, that's really cool. If not, nevermind

girvo• 12 years ago

I triggered it on purpose when I saw your post, by pretending to close the tab. Pretty neat trick!

hardwaresofton2• 12 years ago

Yeah, it looks like they even do it maybe once per IP - I tried to reproduce it but couldn't, even in incognito mode.

Glad I wasn't crazy

Ruby Threads and the Global Interpreter Lock in C

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