ruby-core

Issue #13618 has been updated by funny_falcon (Yura Sokolov).


Considering implementation, `Fiber.transfer` should be used, not `Fiber.resume`+`Fiber.yield`,
ie exclusively use `fiber_switch(..., ..., ..., 0);` and never use `fiber_yield(..., ...)`+`fuber_resume(...,...,...)`.
Reason: to allow nested fiber calls to be scheduled as well.
Example:

Lets have following class
```ruby
class MyPipe
  def initialize(host, port)
    @con = TCPSocket.new(host, port)
  end
  def pipe
    while s = @con.gets
      yield s
    end
  end
end
mypipe = MyPipe.new
```

Now lets iterate:
```ruby
mypipe.pipe{|s| puts s}
```

So far so good.
But now lets use it as enumerator:
```ruby
mypipe.to_enum(:pipe).each{|s| puts s}
```

BAAHHHMMMM!!!! Either we have to fallback to blocking io at `@conn.gets`,
or `fiber_yield` inside of scheduler will yield our `puts s` block, instead of returning to scheduler.

Both Enumerator and io scheduler could not use same `fiber_yield`.
There should be scheduler fiber as a property of native thread (probably, its main fiber),
and scheduled "Threadlets" should transfer control to it, not yield to.


-------------

Second remark about design: please, do not create new beast!
Ruby has Thread, Fiber, Continuation... It doesn't need new Thread::Light, Fred or any thing else!
Let it be just Thread!!!
In my opinion, Thread should be either "green" by default, or by constructor parameter.
Looks like, for backward compatibility, it is better to have native threads still default:
- first, all disk io heavy application will not magically turn into turtles after Ruby's version upgrade
  (so, Eric's application will work unmodified)
- aside of disk io and network io, there are heavy computations, that are also wrapped with "release GVL".

I think, it could be good to have possibility to specify different scheduler variants:
- `Thread.new(scheduler: :current)` - create thread in a scheduler of current native thread.
- `Thread.new(scheduler: :main)` - create thread in a scheduler of main native thread.
- `Thread.new(scheduler: :new)` - create new native thread, and schedule new thread there.
- `Thread.new(scheduler: other_thread.scheduler)` - create new thread in a scheduler of other thread.
- `Thread.new(scheduler: :exclusive)` - create new native thread without scheduler, and run Thread on a native thread stack.

Default `Thread.new` should be synonym for `Thread.new(scheduler: :new)` or `Thread.new(scheduler: :exclusive)`.

Mutex and Queue should be aware of new scheduling model, because there will be only one Thread class.

To be honest, I'd prefer Thread to be green by default.
But given, it is desirable to accept this change before 3.0, it is better to keep compatible behavior, i think.

----------------------------------------
Feature #13618: [PATCH] auto fiber schedule for rb_wait_for_single_fd and rb_waitpid
https://bugs.ruby-lang.org/issues/13618#change-72798

* Author: normalperson (Eric Wong)
* Status: Assigned
* Priority: Normal
* Assignee: normalperson (Eric Wong)
* Target version: 
----------------------------------------
```
auto fiber schedule for rb_wait_for_single_fd and rb_waitpid

Implement automatic Fiber yield and resume when running
rb_wait_for_single_fd and rb_waitpid.

The Ruby API changes for Fiber are named after existing Thread
methods.

main Ruby API:

    Fiber#start -> enable auto-scheduling and run Fiber until it
		   automatically yields (due to EAGAIN/EWOULDBLOCK)

The following behave like their Thread counterparts:

    Fiber.start - Fiber.new + Fiber#start (prelude.rb)
    Fiber#join - run internal scheduler until Fiber is terminated
    Fiber#value - ditto
    Fiber#run - like Fiber#start (prelude.rb)

Right now, it takes over rb_wait_for_single_fd() and
rb_waitpid() function if the running Fiber is auto-enabled
(cont.c::rb_fiber_auto_sched_p)

Changes to existing functions are minimal.

New files (all new structs and relations should be documented):

    iom.h - internal API for the rest of RubyVM (incomplete?)
    iom_internal.h - internal header for iom_(select|epoll|kqueue).h
    iom_epoll.h - epoll-specific pieces
    iom_kqueue.h - kqueue-specific pieces
    iom_select.h - select-specific pieces
    iom_pingable_common.h - common code for iom_(epoll|kqueue).h
    iom_common.h - common footer for iom_(select|epoll|kqueue).h

Changes to existing data structures:

    rb_thread_t.afrunq   - list of fibers to auto-resume
    rb_vm_t.iom          - Ruby I/O Manager (rb_iom_t) :)

Besides rb_iom_t, all the new structs are stack-only and relies
extensively on ccan/list for branch-less, O(1) insert/delete.

As usual, understanding the data structures first should help
you understand the code.

Right now, I reuse some static functions in thread.c,
so thread.c includes iom_(select|epoll|kqueue).h

TODO:

    Hijack other blocking functions (IO.select, ...)

I am using "double" for timeout since it is more convenient for
arithmetic like parts of thread.c.   Most platforms have good FP,
I think.  Also, all "blocking" functions (rb_iom_wait*) will
have timeout support.

./configure gains a new --with-iom=(select|epoll|kqueue) switch

libkqueue:

  libkqueue support is incomplete; corner cases are not handled well:

    1) multiple fibers waiting on the same FD
    2) waiting for both read and write events on the same FD

  Bugfixes to libkqueue may be necessary to support all corner cases.
  Supporting these corner cases for native kqueue was challenging,
  even.  See comments on iom_kqueue.h and iom_epoll.h for
  nuances.

Limitations

Test script I used to download a file from my server:
----8<---
require 'net/http'
require 'uri'
require 'digest/sha1'
require 'fiber'

url = 'http://80x24.org/git-i-forgot-to-pack/objects/pack/pack-97b25a76c03b489d4cbbd85b12d0e1ad28717e55.idx'

uri = URI(url)
use_ssl = "https" == uri.scheme
fibs = 10.times.map do
  Fiber.start do
    cur = Fiber.current.object_id
    # XXX getaddrinfo() and connect() are blocking
    # XXX resolv/replace + connect_nonblock
    Net::HTTP.start(uri.host, uri.port, use_ssl: use_ssl) do |http|
      req = Net::HTTP::Get.new(uri)
      http.request(req) do |res|
    dig = Digest::SHA1.new
    res.read_body do |buf|
      dig.update(buf)
      #warn "#{cur} #{buf.bytesize}\n"
    end
    warn "#{cur} #{dig.hexdigest}\n"
      end
    end
    warn "done\n"
    :done
  end
end

warn "joining #{Time.now}\n"
fibs[-1].join(4)
warn "joined #{Time.now}\n"
all = fibs.dup

warn "1 joined, wait for the rest\n"
until fibs.empty?
  fibs.each(&:join)
  fibs.keep_if(&:alive?)
  warn fibs.inspect
end

p all.map(&:value)

Fiber.new do
  puts 'HI'
end.run.join
```


---Files--------------------------------
0001-auto-fiber-schedule-for-rb_wait_for_single_fd-and-rb.patch (82.8 KB)


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