Nokogiri VS Concurrent Ruby

release planning: v1.16.0 · Issue #2897 · sparklemotion/nokogiri

What's holding me back from going all in with Crystal is I have a lot of pre-existing Ruby code, and porting Ruby code to Crystal can be tricky. For example, Crystal lacks an Enumerator class (aka generators) due to captured block semantics. I also wish the shards ecosystem was a little more mature; for example there's multiple HTML parsing libraries, but none have all of the features that Ruby's Nokogiri has. For new greenfield backend projects, I would totally use Crystal.

Welcome! Ruby isn't exactly "dying", but the hype/popularity is definitely fading. This is primarily because Ruby is no longer "new", most of Ruby's popularity came from Rails, and now Rails is no longer the "new hotness". However, Ruby still has lots of awesome features and lots of awesome other libraries and frameworks, such as the new fancy irb gem that uses reline, nokogiri, chunky_png, the async gems, Dragon Ruby, SciRuby, Ronin, and the new Hanami web framework.

great for hacking at xml

Mike has worked hard over the years to have Nokogiri come with its dependencies. It does come with libxml and all that is required.

From https://nokogiri.org

> These dependencies are met by default by Nokogiri's packaged versions of the libxml2 and libxslt source code, but a configuration option --use-system-libraries is provided to allow specification of alternative library locations.

Some authors work hard to have their tools do the right thing and consistently.

If the page is rendered as html you can use Nokogiri. It has great support and is pretty easy to get started with too.

And even now, pulling in a Java-based HTML5 parser is still probably easier than re-implementing in FFI, which is why I created https://github.com/sparklemotion/nokogiri/issues/2227 and would love to have this the conversation there if possible.

After this, I took a look at the semaphore class in the popular library, concurrent-ruby to see how they implement it, and I learnt about something new: condition variables. And Ruby comes with this included!

https://github.com/ruby-concurrency/concurrent-ruby has great docs if someone is looking for alternatives.

I wonder how this would compare to using concurrent-ruby under ruby 2.7, especially in a real-world setting (where the calls are actually to external services that return and buffer data, instead of just sleep). The author says that he's felt that ruby threads "feel easy to mess up," but I've found that concurrent-ruby makes it pretty simple, and performant enough even with the GIL.

As I could not find a clear example about how to rescue exceptions from Concurrent::Promises (part of the Concurrent Ruby gem ) I read through the documentation and here are two examples: one that documents success case and one that shows what is happening when there is an error.

In a sense the GIL (or actually GVL as it's called in current ruby versions) has already been removed for ruby.

It's only the original MRI Ruby that still has it several over Ruby implementations already removed it. e.g. JRuby.

Concurrent-Ruby[1] is probably a good place to start if you want to work with GVL free ruby on JRuby. It's quite well supported and is currently used by Rails.

If you just want async or non-blocking IO I'd take a look at the Async Gem[2]. It looks pretty solid in Ruby > 3.0 and it's been invited by Matz to be part of the stdlib, which I think is a pretty good endorsement.

For MRI itself I don't think it's likely they'll ever remove the GVL. Ractors are probably a better solution for CPU concurrency in the long run, although I think they're pretty experimental currently.

1. https://github.com/ruby-concurrency/concurrent-ruby

I like how the article exposes you to tools to prove/disprove the problem. I would have hoped it introduced to tools like concurrent ruby and the use of atomics like u/Freeky already mentioned though.

Using conccurrent-ruby, how can I execute a set of promises and then get the results?

I’d highly recommend the concurrent-ruby gem that has implementations of various metaphors of concurrency, from async to promises, as well as edge features such as actors.

You may want to consider using something like concurrent-ruby that provides nice abstractions over multithreading.