Archive for category ruby

MacRuby on iOS – RubyMotion review

Yesterday, RubyMotion was released and let’s be honest, it is one the best alternatives to Objective-C out there (if not the best).

RubyMotion is a commercial, proprietary fork of MacRuby that targets iOS. This is not a small achievement, MacRuby relies on Objective C’s Garbage Collector (libauto) which is not available on iOS. Static compilation and new memory management solution was required to target the iOS platform . The new runtime had to be small and efficient. Furthermore, being able to run code on iOS isn’t enough, you need tools to interact with the compiler, to debug, to packages applications etc…

I don’t think anyone will contest the fact that RubyMotion is a well done product. The question however is, “is it worth for you to invest some money, time and energy in this product instead of using Apple’s language and tools“. In this article, I’ll try to balance the pros and cons of RubyMotion so you can have a better understanding of what RubyMotion could mean for you. As a disclaimer I should say that I was beta testing RubyMotion, that they are strong ties between RubyMotion and the MacRuby project I’m part of and finally that having MacRuby on iOS has been something I’ve been looking forward for a very long time.

Over the last few months I’ve seen RubyMotion take shape and finally hit the big 1.0. As you can see from Twitter and HackerNews, the Ruby community is excited about being able to use their language to write statically compiled, native iOS apps. Spoiler alert, they are right, it’s a lot of fun.

 


 

What I like about RubyMotion:

Ruby Language

I don’t mind Objective-C, I think it’s a fine superset of C, with the arrival of blocks, new literals and automatic memory management via ARC, Objective-C is actually getting better over time. But frankly, it’s not Ruby. You still have to deal with headers, you always have to compile your code via some weird Xcode voodoo settings, testing is a pain, the language, even with the new literals is quite verbose. On the other hand, using Ruby syntax I can get much more flexibility, reuse my code via mixins, easily reopen existing classes etc… At the end of the day, I end up with some code that seems cleaner, easier to understand and maintain even though I’m calling the same underlying APIs. Ruby’s flexibility also allows developers to make their own higher level APIs, take a look at some of the wrappers/helpers I wrote while playing with RubyMotion.

Matt Aimonetti - Ruby Logo

MacRuby

RubyMotion is based on MacRuby, meaning that all the time and energy invested in the project will benefit RubyMotion’s users. All the concepts I explain in my MacRuby book apply to RubyMotion. You don’t have to find workarounds to work with native APIs, Ruby objects are Objective-C objects and performance is great. I do regret Apple didn’t decide to embrace MacRuby for iOS but at the same time, even though we lost the Open Source aspect of the project and Apple’s backing, we gained much more flexibility and freedom on Laurent’s part.

REPL/Interactive shell

RubyMotion doesn’t currently have a debugger, but it does have something Objective-C developers don’t have, a REPL working with the simulator. This feature is quite handy when debugging your application or learning the Cocoa APIs. You can click on a visual element in the simulator and start modifying the objects in real time in a terminal window and see the modifications in the simulator. It reminds me of the first time I used firebug to edit the html/css of a web page and saw the changes in real time.

Matt Aimonetti - RubyMotion REPL

Not dependent on Xcode

Xcode is fine when you write Objective-C code, but it crashes often, it has a complicated UI and never really worked well for MacRuby due to the fact that Objective-C and Ruby have different requirements and the that Xcode is not open source. It’s also fully controlled by Apple and doesn’t provide APIs for 3rd party developers. (That said, the Xcode team has often helped out when a new released of Xcode broke MacRuby, so thank you guys).

Being able to use simple rake tasks to compile, simulate and deploy applications is just really really nice. I’m sure we’ll end up with better IDE integration, nice GUIs for some who like that, but in the meantime, as a “hacker”, I really enjoy the simplicity of the Rake tasks and not being forced in using a specific IDE.

 

Memory management

Even though ARC made memory management much easier for Objective-C developers, when using RubyMotion you don’t have to worry about memory (well at least not explicitly, don’t be dumb and create a bazillion objects and hold references to them either). This includes the CoreFoundation objects that you still have to manually manage in Objective-C. Memory management is transparent and in most cases it’s really nice.

 


 

What I like less about RubyMotion

Here is a list of things that are cons to using RubyMotion, note that while the list is longer than my list of “pros”, I listed a lot of small things. I also think that most of these issues will get solved in the next few months.

 

Ruby language

There are some cases where Ruby just isn’t that great or is not an option. Examples include dealing with API relying heavily on pointers, when using some of the lower level APIs or when you have to interact with C++ (video game engines for instance). The good news is that within the same project, you can write part of your code in Objective-C and the rest in RubyMotion. The other thing that bothers me a little bit with writing Ruby code for iOS is that you can’t easily enforce argument types and therefore you are losing a lot of the features provided by Clang to the Objective-C developers. I dream of an optionally typed Ruby — but that’s a different topic.

Another downside of using Ruby is that Ruby developers will assume all standard libraries and gems will be compatible with RubyMotion. This isn’t the case. You need to think of RubyMotion as only offering the Ruby syntax (modulo a few differences). To be honest, most of the std libs and gems aren’t that useful when writing iOS apps. Even when I write MacRuby apps, I rarely rely on them and pick libraries designed to work in a non-blocking, multi-threaded environment (usually ObjC libs that I wrap).

 

Cocoa Touch

If you’re already an iOS/OS X developer, you know that most of the hurdles aren’t the language syntax but the Cocoa APIs. These APIs are what you need to interact with to create your application. Cocoa APIs are usually much lower-level compared to what you usually see in Python, Ruby or even Java. While they are quite consistent, the APIs still have a stiff learning curve and currently,  if you want to write iOS applications, even if you know Ruby, you still have to learn Cocoa.

However, I do think that with RubyMotion now building a userbase, we will start seeing more and more wrappers around these sometimes hideous APIs.

 

No Xcode/IDE

There are cases where an IDE is really practical, especially when learning new APIs. Being able to have code completion, quick access to the documentation, instrumentation, debugging, interface builder, refactoring tools are things that Objective-C developers might have a hard time with when switching to RubyMotion. If you don’t know either Ruby or Cocoa, getting started with RubyMotion might be quite hard and you are probably not currently in the target audience.

 

Writing UI code by hand

In some cases, it makes sense, in other, it should be much easier. I know that Laurent is working on a DSL to make that easier and I’m looking forward to it. But in the mean time, this is quite a painful exercise, especially due to the complexity of the Cocoa UI APIs. Using Xcode’s interface builder and Storyboards is something I know a lot of us wish we could do with RubyMotion when developing specific types of applications.

Matt Aimonetti - Xcode iOS storyboard

No debugger

Again, this is eventually coming but the current lack of debugger can be problematic at times, especially when the problem isn’t obvious.

 

Lack of clear target audience

It’s hard to blame a brand new product for not having clearly defined a target audience. But as a developer I find myself wondering “when should I use RubyMotion and for what kinds of problems?” Is RubyMotion great for quick prototypes I can then turn into production code? Or is good for throw away prototypes? Is it reserved for “fart and flash light” applications? Is it ready for prime time and should I invest and write my new awesome apps using it? Should I convert over my existing code base over from Titanium (or whatever other alternatives you used)? Should I use RubyMotion every time I would use Objective-C?

I guess we will see when the first applications start hitting the app store and people start reporting on their experience.

Documentation

I’m partially to blame here since I could have moved my butt and start writing a book but the point is nonetheless valid. All the iOS documentation out there is for Objective-C, all the APIs and samples provided by Apple are obviously only for Objective-C. Thankfully, you can use the 2 MacRuby books available out there to understand how to convert this existing documentation into something useful, but RubyMotion will need to provide better and more adapted documentation for beginners. I have no doubt that this is coming sooner than later.

 

Proprietary solution

RubyMotion isn’t open source and currently fully relies on the shoulders of a single man. If unfortunately, Laurent goes out of business or decides to do something else then we will have to rewrite our apps in Objective-C.  Using RubyMotion for a professional product represents a significant business risk, which is exactly the same as using proprietary technology from any vendor. Apple could also decide to switch to JavaScript or rewrite iOS in Java and deprecate Objective-C. Let’s just say that it is unlikely.

I usually favor open source solutions, from the programming language I use to the OS I deploy on. This isn’t always possible and if you want to write iOS applications, you don’t currently have a choice. I do wish Laurent had found a way to make money while keeping the source code open. But who knows — after he makes his first million(s), he might change his mind.

Matt Aimonetti - RMS

Conclusion

I would strongly suggest you consider giving RubyMotion a try. I can assure you that it will provide at least a few hours of ‘hacking fun’ (and you will be able to brag about havng written your own iPhone app).  It will also help support financially someone who’s taking a risk in trying to push mobile development to the next level.

RubyMotion is, by far, my favorite alternative to Objective-C. But it is hard to tell, just 48 hours after its release, what people will do with it. Can it transcend the programming language barriers and attract Python, PHP, Java, ObjC and JavaScript developers? What is the sweet spot for RubyMotion applications? Will it affect the native vs web app battle? Can it make iOS development more accessible to the masses? Only time will tell.

What do you think?

 

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Introduction to mruby

A couple days ago, I wrote an introduction article to help developers getting started with mruby (aka mrb).

matt aimonetti - getting started with mruby

Besides explaining the difference between mrb and the other implementations, the article shows concrete examples to embed Ruby inside a C software application. The article doesn’t mention a few nice tricks such as mruby allowing you replace double by float (though still imperfect), the possibility to replace the memory allocator and it was even reported to me that mruby can run on the Lego Mindstorms platform which only has 250K of memory!

mruby is still in alpha stage but it’s getting more interesting every day and at this rate it will soon become a real alternative to Lua.

Learn how to get started with mruby now.

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new Ruby: mruby and mobiruby Ruby for iOS/Android

A few days ago, I wrote an article covering Ruby creator Matz’ new Ruby implementation: mruby and its first related project: MobiRuby which aims to let Ruby developers write iOS and Android applications using their favorite language.

 

Matt Aimonetti article on mruby and MobiRuby

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Quick dive into Ruby ORM object initialization

Yesterday I did some quick digging into how ORM objects are initialized and the performance cost associated to that. In other words, I wanted to see what’s going on when you initialize an ActiveRecord object.

Before I show you the benchmark numbers and you jump to conclusions, it’s important to realize that in the grand scheme of things, the performance cost we are talking is small enough that it is certainly not the main reason why your application is slow. Spoiler alert: ActiveRecord is slow but the cost of initialization isn’t by far the worse part of ActiveRecord. Also, even though this article doesn’t make activeRecord look good, and I’m not trying to diss it. It’s a decent ORM that does a great job in most cases.

Let’s get started by the benchmarks number to give us an idea of the damage (using Ruby 1.9.3 p125):

 

                                                             | Class | Hash  | AR 3.2.1 | AR no protection | Datamapper | Sequel |
--------------------------------------------------------------------------------------------------------------------------------------
.new() x100000                                               | 0.037 | 0.049 | 1.557    | 1.536            | 0.027      | 0.209  |
.new({:id=>1, :title=>"Foo", :text=>"Bar"}) x100000          | 0.327 | 0.038 | 6.784    | 5.972            | 4.226      | 1.986  |

 

You can see that I am comparing the allocation of a Class instance, a Hash and some ORM models. The benchmark suite tests the allocation of an empty object and one with passed attributes. The benchmark in question is available here.

As you can see there seems to be a huge performance difference between allocating a basic class and an ORM class. Instantiating an ActiveRecord class is 20x slower than instantiating a normal class, while ActiveRecord offers some extra features, why is it so much slower, especially at initialization time?

The best way to figure it out is to profile the initialization. For that, I used perftools.rb and I generated a graph of the call stack.

Here is what Ruby does (and spends its time) when you initialize a new Model instance (click to download the PDF version):

 

Profiler diagram of AR model instantiation by Matt Aimonetti

 

This is quite a scary graph but it shows nicely the features you are getting and their cost associated. For instance, the option of having the before and after initialization callback cost you 14% of your CPU time per instantiation, even though you probably almost never use these callbacks. I’m reading that by interpreting the node called ActiveSupport::Callback#run_callbacks, 3rd level from the top. So 14.1% of the CPU time is spent trying to run callbacks. As a quick note, note that 90.1% of the CPU time is spent initializing objects, the rest is spent in the loop and in the garbage collection (because the profiler runs many loops). You can then follow the code and see how the code works, creating a dynamic class callback method on the fly (the one with the long name) and then recreating the name of this callback to call it each time the object is allocated. It sounds like that’s a good place for some micro optimizations which could yield up to 14% performance increase in some cases.

Another major part of the CPU time is spent in ActiveModel’s sanitization. This is the piece of code that allows you to block some model attributes to be mass assigned. This is useful when you don’t want to sanitize your incoming params but want to create or update a model instance by using all the passed user params. To avoid malicious users to modify some specific params that might be in your model but not in your form, you can protect these attributes. A good example would be an admin flag on a User object. That said, if you manually initialize an instance, you don’t need this extra protection, that’s why in the benchmark above, I tested and without the protection. As you can see, it makes quite a big difference. The profiler graph of the same initialization without the mass assignment protection logically ends up looking quite different:

 


Matt Aimonetti shows the stack trace generated by the instantiation of an Active Record model

 

Update: My colleague Glenn Vanderburg pointed out that some people might assuming that the shown code path is called for each record loaded from the database. This isn’t correct, the graph represents instances allocated by calling #new. See the addition at the bottom of the post for more details about what’s going on when you fetch data from the DB.

I then decided to look at the graphs for the two other popular Ruby ORMs:

Datamapper

 

and Sequel

 

 

While I didn’t give you much insight in ORM code, I hope that this post will motivate you to sometimes take a look under the cover and profile your code to see what’s going on and why it might be slow. Never assume, always measure. Tools such as perftools are a great way to get a visual feedback and get a better understanding of how the Ruby interpreter is handling your code.

UPDATE:

I heard you liked graphs so I added some more, here is what’s going on when you do Model.first:

 

Model.all

 

And finally this is the code graph for a call to Model.instantiate which is called after a record was retrieved from the database to convert into an Object. (You can see the #instantiate call referenced in the graph above).

 

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My RubyConf 2011 talk is online

I realize I forgot to mention that my RubyConf talk is now online on the confreaks site (wait until the end, Matz actually answers a question from the audience).

Photo of Matt Aimonetti giving a talk at RubyConf 2011 with one of his slides showing how thread scheduling works

I wrote a couple follow up posts you might also be interested in:

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Data safety and GIL removal

After my recent RubyConf talk and follow up post addressing the Ruby & Python’s Global Interpreter Lock (aka GVL/Global VM Lock). a lot of people asked me to explain what I meant by “data safety”. While my point isn’t to defend one approach or the other, I spent a lot of time explaining why C Ruby and C Python use a GIL and where it matters and where it matters less. As a reminder and as mentioned by Matz himself, the main reason why C Ruby still has a GIL is data safety. But if this point isn’t clear to you, you might be missing the main argument supporting the use of a GIL.

Showing obvious concrete examples of data corruption due to unsafe threaded code isn’t actually as easy at it sounds. First of all, even with a GIL, developers can write unsafe threaded code. So we need to focus only on the safety problems raised by removing the GIL. To demonstrate what I mean, I will try to create some race conditions and show you the unexpected results you might get. Again, before you go crazy on the comments, remember that threaded code is indeterministic and the code below might potentially work on your machine and that’s exactly why it is hard to demonstrate. Race conditions depend on many things, but in this case I will focus on race conditions affecting basic data structures since it might be the most surprising.

Example:

@array, threads = [], []
4.times do
  threads << Thread.new { (1..100_000).each {|n| @array << n} }
end
threads.each{|t| t.join }
puts @array.size

In the above example, I’m creating an instance variable of Array type and I start 4 threads. Each of these threads adds 100,000 items to the array. We then wait for all the threads to be done and check the size of the array.

If you run this code in C Ruby the end result will be as expected:

400000

Now if you switch to JRuby you might be surprised by the output. If you are lucky you will see the following:

ConcurrencyError: Detected invalid array contents due to unsynchronized modifications with concurrent users
        << at org/jruby/RubyArray.java:1147
  __file__ at demo.rb:3
      each at org/jruby/RubyRange.java:407
  __file__ at demo.rb:3
      call at org/jruby/RubyProc.java:274
      call at org/jruby/RubyProc.java:233

This is actually a good thing. JRuby detects that you are unsafely modifying an instance variable across threads and that data corruption will occur. However, the exception doesn’t always get raised and you will potentially see results such as:

335467
342397
341080

This is a sign that the data was corrupted but that JRuby didn’t catch the unsynchronized modification. On the other hand MacRuby and Rubinius 2 (dev) won’t raise any exceptions and will just corrupt the data, outputting something like:

294278
285755
280704
279865

In other words, if not manually synchronized, shared data can easily be corrupted. You might have two threads modifying the value of the same variable and one of the two threads will step on top of the other leaving you with a race condition. You only need 2 threads accessing the same instance variable at the same time to get a race condition. My example uses more threads and more mutations to make the problem more obvious. Note that TDD wouldn’t catch such an issue and even extensive testing will provide very little guarantee that your code is thread safe.

 

So what? Thread safety isn’t a new problem.

That’s absolutely correct, ask any decent Java developer out there, he/she will tell how locks are used to “easily” synchronize objects to make your code thread safe. They might also mention the deadlocks and other issues related to that, but that’s a different story. One might also argue that when you write web apps, there is very little shared data and the chances of corrupting data across concurrent requests is very small since most of the data is kept in a shared data store outside of the process.

All these arguments are absolutely valid, the challenge is that you have a large community and a large amount of code out there that expects a certain behavior. And removing the GIL does change this behavior. It might not be a big deal for you because you know how to deal with thread safety, but it might be a big deal for others and C Ruby is by far the most used Ruby implementation. It’s basically like saying that automatic cars shouldn’t be made and sold, and everybody has to switch to stick shifts. They have better gas mileage, I personally enjoy driving then and they are cheaper to build. Removing the GIL is a bit like that. There is a cost associated with this decision and while this cost isn’t insane, the people in charge prefer to not pay it.

 

Screw that, I’ll switch to Node.js

I heard a lot of people telling me they were looking into using Node.js because it has a better design and no GIL. While I like Node.js and if I were to implement a chat room or an app keeping connections for a long time, I would certainly compare it closely to EventMachine, I also think that this argument related to the GIL is absurd. First, you have other Ruby implementations which don’t have a GIL and are really stable (i.e: JRuby) but then Node basically works the same as Ruby with a GIL. Yes, Node is evented and single threaded but when you think about it, it behaves the same as Ruby 1.9 with its GIL. Many requests come in and they are handled one after the other and because IO requests are non-blocking, multiple requests can be processed concurrently but not in parallel. Well folks, that’s exactly how C Ruby works too, and unlike popular believe, most if not all the popular libraries making IO requests are non blocking (when using 1.9). So, next time you try to justify you wanting to toy with Node, please don’t use the GIL argument.

 

What should I do?

As always, evaluate your needs and see what makes sense for your project. Start by making sure you are using Ruby 1.9 and your code makes good use of threading. Then look at your app and how it behaves, is it CPU-bound or IO-bound. Most web apps out there are IO-bound (waiting for the DB, redis or API calls), and when doing an IO call, Ruby’s GIL is released allowing another thread to do its work. In that case, not having a GIL in your Ruby implementation won’t help you. However, if your app is CPU-bound, then switching to JRuby or Rubinius might be beneficial. However, don’t assume anything until you proved it and remember that making such a change will more than likely require some architectural redesign, especially if using JRuby.  But, hey, it might totally be worth it as many proved it in the past.

 

I hope I was able to clarify things a bit further. If you wish to dig further, I would highly recommend you read the many discussions the Python community had in the last few years.

 

 

 

 

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About concurrency and the GIL

During RubyConf 2011, concurrency was a really hot topic. This is not a new issue, and the JRuby team has been talking about true concurrency for quite a while . The Global Interpreter Lock has also been in a subject a lot of discussions in the Python community and it’s not surprising that the Ruby community experiences the same debates since the evolution of their implementations are somewhat similar. (There might also be some tension between EngineYard hiring the JRuby and Rubinius teams and Heroku which recently hired Matz (Ruby’s creator) and Nobu, the #1 C Ruby contributor)

The GIL was probably even more of a hot topic now that Rubinius is about the join JRuby and MacRuby in the realm of GIL-less Ruby implementations.

During my RubyConf talk (slides here), I tried to explain how C Ruby works and why some decisions like having a GIL were made and why the Ruby core team isn’t planning on removing this GIL anytime soon. The GIL is something a lot of Rubyists love to hate, but a lot of people don’t seem to question why it’s here and why Matz doesn’t want to remove it. Defending the C Ruby decision isn’t quite easy for me since I spend my free time working on an alternative Ruby implementation which doesn’t use a GIL (MacRuby). However, I think it’s important that people understand why the MRI team (C Ruby team) and some Pythonistas feels so strongly about the GIL.

What is the GIL?

Here is a quote from the Python wiki:

In CPython, the global interpreter lock, or GIL, is a mutex that prevents multiple native threads from executing Python bytecodes at once. This lock is necessary mainly because CPython’s memory management is not thread-safe. (However, since the GIL exists, other features have grown to depend on the guarantees that it enforces.) [...] The GIL is controversial because it prevents multithreaded CPython programs from taking full advantage of multiprocessor systems in certain situations. Note that potentially blocking or long-running operations, such as I/O, image processing, and NumPy number crunching, happen outside the GIL. Therefore it is only in multithreaded programs that spend a lot of time inside the GIL, interpreting CPython bytecode, that the GIL becomes a bottleneck.

The same basically applies to C Ruby. To illustrate the quote above, here is a diagram representing two threads being executed by C Ruby:

Fair thread scheduling in Ruby by Matt Aimonetti

Such a scheduling isn’t a problem at all when you only have 1 cpu, since a cpu can only execute a piece of code at a time and context switching happens all the time to allow the machine to run multiple processes/threads in parallel. The problem is when you have more than 1 CPU because in that case, if you were to only run 1 Ruby process, then you would most of the time only use 1 cpu at a time. If you are running on a 8 cpu box, that’s not cool at all! A lot of people stop at this explanation and imagine that their server can only handle one request at a time and they they rush to sign Greenpeace petitions asking Matz to make Ruby greener by optimizing Ruby and saving CPU cycles. Well, the reality is slightly different, I’ll get back to that in a minute. Before I explain “ways to achieve true concurrency with CRuby, let me explain why C Ruby uses a GIL and why each implementation has to make an important choice and in this case both CPython and C Ruby chose to keep their GIL.

 

Why a GIL in the first place?

  • It makes developer’s lives easier (it’s harder to corrupt data)
  • It avoids race conditions within C extensions
  • It makes C extensions development easier (no write barriers..)
  • Most of the C libraries which are wrapped are not thread safe
  • Parts of Ruby’s implementation aren’t threadsafe (Hash for instance)
As you can see the arguments can be organized in two main categories: data safety and C extensions/implementation. An implementation which doesn’t rely too much on C extensions (because they run a bit slow, or because code written in a different language is preferred) is only faced with one argument: data safety.

 

Should C Ruby remove its GIL?

  • No: it potentially makes Ruby code unsafe(r)
  • No: it would break existing C extensions
  • No: it would make writing C extensions harder
  • No: it’s a lot of work to change make C Ruby threadsafe
  • No: Ruby is fast enough in most cases
  • No: Memory optimization and GC is more important to tackle first
  • No: C Ruby code would run slower
  • Yes: we really need better/real concurrency
  • Yes: Rubber boots analogy (Gustavo Niemeyer)
Don’t count the amount of pros/cons to jump to the conclusion that removing the GIL is a bad idea. A lot of the arguments for removing the GIL are related. At the end of the day it boils down to data safety. During the Q&A section of my RubyConf talk, Matz came up on stage and said data safety was the main reason why C Ruby still has a GIL. Again, this is a topic which was discussed at length in the Python community and I’d encourage you to read arguments from the Jython (the equivalent of JRuby for Python) developers, the PyPy (the equivalent of Rubinius in the Python community) and CPython developers. (a good collection of arguments are actually available in the comments related to the rubber boots post mentioned earlier)

 

How can true concurrency be achieved using CRuby?

  • Run multiple processes (which you probably do if you use Thin, Unicorn or Passenger)
  • Use event-driven programming with a process per CPU
  • MultiVMs in a process. Koichi presented his plan to run multiple VMs within a process.  Each VM would have its own GIL and inter VM communication would be faster than inter process. This approach would solve most of the concurrency issues but at the cost of memory.
Note:  forking a process only saves memory when using REE since it implements a GC patch that makes the forking process Copy on Write friendly. The Ruby core team worked on a patch for Ruby 1.9 to achieve the same result. Nari & Matz are currently working on improving the implementation to make sure overall performance isn’t affected.

Finally, when developing web applications, each thread spend quite a lot of time in IOs which, as mentioned above won’t block the thread scheduler. So if you receive two quasi-concurrent requests you might not even be affected by the GIL as illustrated in this diagram from Yehuda Katz:

This is a simplified diagram but you can see that a good chunk of the request life cycle in a Ruby app doesn’t require the Ruby thread to be active (CPU Idle blocks) and therefore these 2 requests would be processed almost concurrently.

To boil it down to something simplified, when it comes to the GIL, an implementor has to chose between data safety and memory usage. But it is important to note that context switching between threads is faster than context switching between processes and data safety can and is often achieved in environments without a GIL, but it requires more knowledge and work on the developer side.

 

Conclusion

The decision to keep or remove the GIL is a bit less simple that it is often described. I respect Matz’ decision to keep the GIL even though, I would personally prefer to push the data safety responsibility to the developers. However, I do know that many Ruby developers would end up shooting themselves in the foot and I understand that Matz prefers to avoid that and work on other ways to achieve true concurrency without removing the GIL. What is great with our ecosystem is that we have some diversity, and if you think that a GIL less model is what you need, we have some great alternative implementations that will let you make this choice. I hope that this article will help some Ruby developers understand and appreciate C Ruby’s decision and what this decision means to them on a daily basis.

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