ruby-core

Issue #14736 has been updated by ioquatix (Samuel Williams).


For the first case, you naturally can't call Fiber.yield in that context... but this works:

```
#!/usr/bin/env ruby

require 'fiber'

fiber = Fiber.new do
	def aga; yield 1; Fiber.yield 4; yield 8; end
	puts to_enum(:aga).to_a
end

value = fiber.resume
puts "Got #{value}"
while fiber.alive?
	fiber.resume
end

# Prints:
# Got 4
# 1
# 8
```

This also works:

```
#!/usr/bin/env ruby

require 'fiber'

fiber = Fiber.new do
	def aga; yield 1; Fiber.yield 4; yield 8; end
	e = to_enum(:aga)
	
	puts e.next
	puts e.next
	puts e.next
end

value = fiber.resume
puts "Got #{value.inspect}"
while fiber.alive?
	fiber.resume
end

# 1
# 4
# 8
# Got nil
```

The semantics of `Fiber.yield` from within the enumerator block depend on how it's being used. That's not something I was aware of. I see that it fails if you try to do this:

```
#!/usr/bin/env ruby

$LOAD_PATH << File.expand_path("../../lib", __dir__)

require 'async'
require 'async/io/stream'
require 'async/io/host_endpoint'
require 'async/io/protocol/line'

class Lines < Async::IO::Protocol::Line
	def each
		return to_enum unless block_given?
		
		while line = read_line
			yield line
		end
	end
end

input = Lines.new(
	Async::IO::Stream.new(
		Async::IO::Generic.new($stdin)
	)
)

Async.run do
	# This works:
	# input.each do |line|
	# 	puts "... #{line}"
	# end
	
	# This doesn't:
	enumerator = input.each
	while line = enumerator.next
		puts "... #{line}"
	end
end
```

I can imagine, if you don't know the underlying task is asynchronous, that this might cause some frustration, fortunately the error is reasonably clear in this instance.

The problem is the nested fiber is not created in an `Async::Task`. I believe that with this PR in place, it would be possible to avoid this, because ALL Fiber created on the thread with a selector is asynchronous, so it shouldn't be a problem. I am interested in working further on this PR, and this is an interesting test case. Perhaps I will see if it can work or not.

----------------------------------------
Feature #14736: Thread selector for flexible cooperative fiber based concurrency
https://bugs.ruby-lang.org/issues/14736#change-72824

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Ruby concurrency can be greatly enhanced by concurrent, deterministic IO.

Fibers have been shown many times to be a great abstraction for this purpose. The retain normal code flow and don't require any kind of Thread synchronisation. They are enjoyable to write code with because you don't have to concern yourself with thread synchronisation or other complicated issues.

The basic idea is that if some operation would block, it yields the Fiber, and other Fibers within the thread can continue to execute.

There are a number of ways to implement this. Here is a proof of concept to amend the existing `rb_io_wait_readable`/`rb_io_wait_writable`.

https://github.com/ruby/ruby/pull/1870

This design minimally affects the Ruby implementation and allows flexibility for selector implementation. With a small amount of work, we can support EventMachine (65 million downloads), NIO4r (21 million downloads). It would be trivial to back port.

This PR isn't complete but I am seeking feedback. If it's a good idea, I will do my best to see it through to completion, including support for EventMachine and NIO4r.

---Files--------------------------------
port_scanner_threadlet.rb (925 Bytes)


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