# Green threads in 1.9.\*? **URL:** \ **Category:** Ruby\ **Created:** [July 4, 2012, 12:57pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209 "2012-07-04T12:57:16Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![aris](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/258eb7/32.png) [@aris](https://www.ruby-forum.com/u/aris)\ **Post date:** [July 4, 2012, 12:57pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/1 "2012-07-04T12:57:16Z")
I am new to Ruby. I am somewhat surprised that I was not able to find much info on this question via google or searching of forums. I was able to find a similar question posted a while back but no one answered it. Perhaps threads aren’t such an important topic in Ruby culture? Anyway, to the point. I’d like to use green threads (NOT kernel threads) in a Ruby program I’m writing. There is no reason for me to use kernel threads, and every reason to use green ones. Are green threads still available? If so, how do I access/use them (Thread class says nothing about whether it is green or kernel - I suspect kernel)? If not, why not? If not available, are there any alternatives? I checked into fibers, but they are not appropriate for what I want because if an exception happens, it happens in the “main thread” I am executing, which I don’t want. Thanks. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 1:18pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/2 "2012-07-04T13:18:59Z")
Hi, As far as I understand, Ruby 1.9 has native threads, but they’re blocked by the Global Interpreter Lock. So they should work like you want them to. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 1:26pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/3 "2012-07-04T13:26:21Z")
It depends on the interpreter. This post may help you get the picture: [http://www.igvita.com/2008/11/13/concurrency-is-a-myth-in-ruby/](http://www.igvita.com/2008/11/13/concurrency-is-a-myth-in-ruby/) ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 1:52pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/4 "2012-07-04T13:52:36Z")
rex goxman wrote in post #1067385: > Are you saying that green threads are used regardless of what is > happening with kernel threads and the GIL? The link posted by fxn > seems to indicate this. This looks like a mistake. Ruby 1.8 has green threads, Ruby 1.9 and JRuby have native threads (though Ruby 1.9 has a GIL). ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 1:45pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/5 "2012-07-04T13:45:05Z")
@jacques1 and fxn above: Are you saying that green threads are used regardless of what is happening with kernel threads and the GIL? The link posted by fxn seems to indicate this. EDIT: 1.9.x of course. Thanks. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 2:11pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/6 "2012-07-04T14:11:56Z")
On Wed, Jul 4, 2012 at 1:45 PM, rex goxman [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: @jacques1 and fxn above: > Are you saying that green threads are used regardless of what is > happening with kernel threads and the GIL? The thread posted by fxn > seems to indicate this. I don’t know enough to give a definitive answer (or plainly put, to answer), but here’s my interpretation of the post: I believe the green threads in Ilya’s post are the Ruby-land thread objects, they are not necessarily green in the sense of who is doing the scheduling. This is my interpretation a posteriori because of the way the JVM is drawn. They are definitely green threads in MRI 1.8 in the sense that MRI did scheduling (you already know that). Then, behind the scenes, they are mapped to native threads in MRI 1.9 and JRuby. One-to-one. In the case of MRI there’s a GIL. I guess technically a GIL does not mean that MRI is doing the scheduling, it means MRI is holding a lock, but the kernel schedules the native thread (because it is native). Maybe there’s a gray area in the definition of green thread here, I don’t know. That is my interpretation, but I don’t know enough to be certain. Please someone correct me if that is wrong! ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 2:30pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/7 "2012-07-04T14:30:38Z")
rex goxman писал 04.07.2012 16:26: > TCL > version of the same above, which I know uses kernel threads. It only > spawned a couple heavyweights per second. > > I guess the results are indeterminate? Hopefully someone else will > chime in who knows definitively. Ruby 1.9 uses kernel threads and does not have green threads. There is nothing like Erlang’s lightweight processes in Ruby (or, for that matter, in most of the languages). ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 2:42pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/8 "2012-07-04T14:42:20Z")
On Wed, Jul 4, 2012 at 2:30 PM, Peter Z. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: Ruby 1.9 uses kernel threads and does not have green threads. > There is nothing like Erlang’s lightweight processes in Ruby (or, for > that matter, in most of the languages). That is clear, but the definition of green thread depends on who schedules them. Is the GIL acting as a scheduler? Has MRI logic about what to lock next therefore scheduling in practice _among the threads in its process_? Or is my conjecture right that locking is mostly dumb and that ultimately the kernel is the scheduler because the thread is native? ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 2:46pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/9 "2012-07-04T14:46:26Z")
Xavier N. писал 04.07.2012 16:41: > schedules > them. > > Is the GIL acting as a scheduler? Has MRI logic about what to lock > next > therefore scheduling in practice _among the threads in its process_? > Or is > my conjecture right that locking is mostly dumb and that ultimately > the > kernel is the scheduler because the thread is native? The OP’s problem is not the scheduler itself but the associated system resources. You can create 20k Erlang processes (“threads”). You cannot create 20k pthreads. Just that. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 2:26pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/10 "2012-07-04T14:26:30Z")
If jacques1 is right, then there are no green threads, just kernel threads, and I’m out of luck (anyone know why they would do away with green threads instead of keeping them and also adding kernel threads?). I did a quick-and-dirty test here (ruby 1.9.3) to try to shed some light. My assumption is that green threads should be incredibly cheap to create (on the order of at least thousands per second), where as kernel threads should be much, much slower. (1…5000).each {Thread.new{}} This takes around 12 seconds to execute on my machine. It seems far too slow for green threads (I can create hundreds of thousands of green processes in erlang per second). However, someone out there correct me if I am wrong, but I would also expect kernel threads to be much slower than the above, i.e. on the order of a few per second. I coded up a TCL version of the same above, which I know uses kernel threads. It only spawned a couple heavyweights per second. I guess the results are indeterminate? Hopefully someone else will chime in who knows definitively. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 4:56pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/11 "2012-07-04T16:56:59Z")
You could try to emulate green threads using a native thread pool + fibers. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 3:00pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/12 "2012-07-04T15:00:27Z")
On Wed, Jul 4, 2012 at 2:45 PM, Peter Z. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: Xavier N. писал 04.07.2012 16:41: > > > > resources. > You can create 20k Erlang processes (“threads”). You cannot create 20k > pthreads. Just that. Looks so also to me, but Ilya’s post makes that clear (and it is a known characteristic of MRI 1.9)… why the followup then after I linked to the post? ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 6:13pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/13 "2012-07-04T18:13:27Z")
Peter Z. wrote in post #1067393: > There is nothing like Erlang’s lightweight processes in Ruby (or, for > that matter, in most of the languages). Well, for the purposes here, if Ruby’s threads were green threads, yes they would have been comparable to Erlang green processes. My emphasis is far more on the “green” and far less on whether it is a process or a thread. As far as the definition of green and whether it has anything to do with a scheduler or not, my definition of green is simply whether or not it is a ‘real’ thread or simply a virtual thread which lives inside of the vm. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 5:19pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/14 "2012-07-04T17:19:37Z")
You might also want to look into tarcieri’s celluloid: > **[GitHub - celluloid/celluloid: Actor-based concurrent object framework for Ruby](https://github.com/celluloid/celluloid/)** > > Actor-based concurrent object framework for Ruby. Contribute to celluloid/celluloid development by creating an account on GitHub. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 6:24pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/15 "2012-07-04T18:24:02Z")
rex goxman wrote in post #1067433: > Well, for the purposes here, if Ruby’s threads were green threads, yes > they would have been comparable to Erlang green processes. My emphasis > is far more on the “green” and far less on whether it is a process or a > thread. Ruby 1.8 _has_ green threads. It’s explained in Xavier’s link, and I also mentioned it above. You seem to misread “some implementations have native threads” as “all have native threads”. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 4, 2012, 7:03pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/16 "2012-07-04T19:03:11Z")
Jan E. wrote in post #1067435: > rex goxman wrote in post #1067433: > > > Well, for the purposes here, if Ruby’s threads were green threads, yes > > they would have been comparable to Erlang green processes. My emphasis > > is far more on the “green” and far less on whether it is a process or a > > thread. > > Ruby 1.8 _has_ green threads. It’s explained in Xavier’s link, and I > also mentioned it above. > > You seem to misread “some implementations have native threads” as “all > have native threads”. The title of this post is “green threads in 1.9.\* ?” Furthermore, I have this edit in one of my posts here: > EDIT: 1.9.x of course. So I have misread nothing. I am **ONLY** talking about 1.9.\*. I could care less about 1.8 or any other implementation. Thanks. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 5, 2012, 3:31am UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/17 "2012-07-05T03:31:17Z")
On Wed, Jul 4, 2012 at 3:57 AM, rex goxman [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I’d like to use green threads (NOT kernel threads) in a Ruby program I’m > writing. There is no reason for me to > use kernel threads, and every reason to use green ones. If you want to use 1.9, you’re out of luck. That said, you aren’t stating your reasoning for why you would prefer green threads over native ones. Native threads have a longer creation time and use marginally more memory (they use ~20kB per thread last I measured), however they generally perform better, particularly around I/O. On platforms like Linux scheduling is O(1) so there’s really no reason you can’t create large numbers of threads. There are definitely many reasons to prefer native threads over green threads. This is the reason why you have seen a shift from green threads to native threads in MRI, Rubinius, and the JVM. Why do you want green threads? ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 5, 2012, 1:40am UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/18 "2012-07-05T01:40:18Z")
On 5 July 2012 03:03, rex goxman [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > So I have misread nothing. I am **ONLY** talking about 1.9.\*. I could > care less about 1.8 or any other implementation. Couldn’t. Unless your level of caring is greater than your minimum. Or you can have negative carativitiy. I’m pretty sure Xavier (fxn) has answered this thread pretty well. My question is: do you really care about the greenness of the threads (academically), or do you actually want to know how best to utilise them since they seem to have unusual profiling characteristics? If the former, I don’t know what to suggest. Research, code scouring, reverse engineering (or read the link posted earlier). If the latter, I say explore and research, and if you find something that works best for your application use it, and maybe share it with us in case we need to do it again some day. As an aside, and I’m not pointing the finger at anyone in this thread when I say this, but a week or two ago I commented to a colleague of mine about how polite the ruby-talk forum was, and how people seemed to consciously avoid flaming and trolling, and how noobs got useful help even when they asked “dumb noob” questions, and how people said “thank you” . . . but in the past couple of days there’ve been a few discussions (usually related to optimisation or performance) that have developed a very negative tone, if not outright ALL CAPS TYPING and rage. What’s going on? I want a return to the happy, friendly ruby-talk of yesterweek. – Matthew K., B.Sc (CompSci) (Hons) [http://matthew.kerwin.net.au/](http://matthew.kerwin.net.au/) ABN: 59-013-727-651 “You’ll never find a programming language that frees you from the burden of clarifying your ideas.” - xkcd ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 5, 2012, 3:34am UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/19 "2012-07-05T03:34:13Z")
On Wed, Jul 4, 2012 at 5:11 AM, Xavier N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Then, behind the scenes, they are mapped to native threads in MRI 1.9 and > JRuby. One-to-one. In the case of MRI there’s a GIL. I guess technically a > GIL does not mean that MRI is doing the scheduling, it means MRI is holding > a lock, but the kernel schedules the native thread (because it is native). > Maybe there’s a gray area in the definition of green thread here, I don’t > know. MRI is still doing the scheduling in 1.9. It runs a timer thread that interrupts running threads after a certain amount of time so waiting threads can run. This way a single thread doing some computationally intensive operation doesn’t monopolize the entire VM. ---
**Author:** ![rex-goxman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/9d8465/32.png) [@rex-goxman](https://www.ruby-forum.com/u/rex-goxman)\ **Post date:** [July 5, 2012, 3:36pm UTC](https://www.ruby-forum.com/t/green-threads-in-1-9/221209/20 "2012-07-05T15:36:40Z")
\<\\> There are many situations to prefer green threads over kernel threads. It’s why I’m somewhat surprised that Ruby is just ditching green threads, vs. keeping them and deploying kernel threads along side them. Perhaps it’s a cultural thing. Rubyists might be more concerned with things like web servers (Rails development) and what not, and perhaps haven’t found want or need for green threads so much (just a guess). One reason to prefer green threads is if your application doesn’t need speed up through concurrency/parallelism, rather you want a threaded solution for algorithmic purposes, convenience purposes, or other purposes. This is a crappy example, but say you need to do some calculation which might fail or even crash, but you don’t want (or need) to check the inputs to the calculation, or wrap the thing up in an error catching mechanism, or anything of this nature. You just want to calculate it, and if it works, fine, and if it doesn’t (or even crashes) - fine, your main program continues to run. So spawn a green thread to run the calculation. If it works, great. If it crashes, who cares? You might say “do that with a kernel thread.” But what if I want to spawn this thread over and over again in a tight loop? I don’t want or need the monstrous overhead of a kernel thread here. I just want a green thread. Again, there’s a whole host of situations where one might want to have green threads vs. kernel threads. But I wasn’t here to debate that - if Rubyists want to throw green threads in the garbage, that’s their prerogative. I was just here to ask whether there were green threads or not (in 1.9.\*). [Next page](https://www.ruby-forum.com/t/green-threads-in-1-9/221209.md?page=2)