From: "matz (Yukihiro Matsumoto) via ruby-core" <ruby-core@...>
Date: 2026-10-07T08:43:15+00:00
Subject: [ruby-core:126967] [Ruby Feature#11817] map.parallel

Issue #11817 has been updated by matz (Yukihiro Matsumoto).

Status changed from Open to Closed

Thank you for bringing a concrete use case.

For I/O-bound work like yours, this already works today:

```ruby
results = items.map { |item| Thread.new { process(item) } }.map(&:value)
```

Beyond that, a built-in method has to decide the things @rkh listed: which execution unit to use, how many run at once, and what happens to the others when one fails. I don't see a single answer that fits everyone, so for now I think this belongs to gems such as `async`, `concurrent-ruby` or `parallel`.

Matz.

----------------------------------------
Feature #11817: map.parallel
https://bugs.ruby-lang.org/issues/11817#change-119364

* Author: eike.rb (Eike Dierks)
* Status: Closed
----------------------------------------
I'd like to suggest a new method: #parallel

That method should take care of executing workloads in parallel across multiple cores.

I believe that #map can sometimes be distributed to many simultaneous threads.

So we would spread out the map blocks into parallel processing,
and then collect the results in order.

I believe this would need some new infrastructure like apple did with great_central,
so I'm talking along these lines.
(Aka we only want to open up as many threads as there are cores)

This would not help much with a simple map (because we need to collect and serialize the results in the end)
but it could be cool for more complex mappings.

Maybe this should have been a rails topic first,
because there it might make a lot of sense to render partials in parallel,
this could really speed up rails response rendering ;-)

But I believe this is a topic for ruby in general.
Given that we now go to really many cores,
it should be at the heart of ruby to use that.

For a start we could just declare #parallel as -> return self.
and than improve on it.

A naive implementation would just open a new thread for every parallel map block,
but that would not work well -- it actually would be very slow.

So we actually need a thread management,
along the lines of great central.

I believe this should be built into the very core libs of the ruby language.

I know this is hard stuff, but it needs to be done.
Let's go parallel from the heart of the language.

---


Please let us discuss if adding the #parallel method would be a good idea.
Let's come up with some implementations to find the problems.

I'm explicitly referring to map#parallel here.
In rails that might be cache.parallel (if you followed)

for some math tasks it might also be
   parallel do {}



































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