From: "Dan0042 (Daniel DeLorme) via ruby-core" <ruby-core@...>
Date: 2024-11-05T16:38:09+00:00
Subject: [ruby-core:119744] [Ruby master Feature#20855] Introduce `Fiber::Scheduler#blocking_region` to avoid stalling the event loop.

Issue #20855 has been updated by Dan0042 (Daniel DeLorme).


I also don't understand this patch. `Zlib.deflate` is a CPU-bound operation right? So it makes sense for Fibers of the same Thread to execute the 10 operations sequentially. That's what Fibers are about. If you want parallelism you need Threads or Ractors. It seems like this is transforming Fiber::Scheduler into a generic FiberAndOrThreadScheduler? That can't be right.

----------------------------------------
Feature #20855: Introduce `Fiber::Scheduler#blocking_region` to avoid stalling the event loop.
https://bugs.ruby-lang.org/issues/20855#change-110408

* Author: ioquatix (Samuel Williams)
* Status: Open
----------------------------------------
The current Fiber Scheduler performance can be significantly impacted by blocking operations that cannot be deferred to the event loop, particularly in high-concurrency environments where Fibers rely on non-blocking operations for efficient task execution.

## Problem Description

Fibers in Ruby are designed to improve performance and responsiveness by allowing concurrent tasks to proceed without blocking one another. However, certain operations inherently block the fiber scheduler, leading to delayed execution across other fibers. When blocking operations are inevitable, such as system or CPU bound operations without event-loop support, they create bottlenecks that degrade the scheduler's overall performance.

## Proposed Solution

The proposed solution in PR https://github.com/ruby/ruby/pull/11963 introduces a `blocking_region` hook in the fiber scheduler to improve handling of blocking operations. This addition allows code that releases the GVL (Global VM Lock) to be lifted out of the event loop, reducing the performance impact on the scheduler during blocking calls. By isolating these operations from the primary event loop, this enhancement aims to improve worst case performance in the presence of blocking operations.

### `blocking_region(work)`

The new, optional, fiber scheduler hook `blocking_region` accepts an opaque callable object `work`, which encapsulates work that can be offloaded to a thread pool for execution. If the hook is not implemented `rb_nogvl` executes as usual.

## Example

```ruby
require "zlib"
require "async"
require "benchmark"

DATA = Random.new.bytes(1024*1024*100)

duration = Benchmark.measure do
  Async do
    10.times do
      Async do
        Zlib.deflate(DATA)
      end
    end
  end
end

# Ruby 3.3.4: ~16 seconds
# Ruby 3.4.0 + PR: ~2 seconds.
```


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clipboard-202411060314-mby8k.png (120 KB)


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