Rework implementation to use Fiber#transfer. Fixes #23.

Ruby 3 allows mixing `Fiber#resume/#yield` and `Fiber#transfer`. We can
take advantage of that to minimise the impact of non-blocking operations
on user flow control.

Previously, non-blocking operations would invoke `Fiber.yield` and this
was a user-visible side-effect. We did take advantage of it, but it also
meant that integration of Async with existing usage of Fiber could be
problematic. We tracked the most obvious issues in `enumerator_spec.rb`.

Now, non-blocking operations transfer directly to the scheduler fiber
and thus don't impact other usage of resume/yield.

.github/workflows/development.yml

@@ -14,10 +14,7 @@ jobs:
           - macos
 
         ruby:
-          - 2.5
-          - 2.6
-          - 2.7
-          - 3.0
+          - head
 
         experimental: [false]
         env: [""]
@@ -34,7 +31,7 @@ jobs:
             ruby: head
             experimental: true
           - os: ubuntu
-            ruby: 2.6
+            ruby: head
             env: COVERAGE=PartialSummary,Coveralls
             experimental: true
 

async.gemspec

@@ -13,10 +13,11 @@ Gem::Specification.new do |spec|
 
 	spec.files = Dir.glob('{lib}/**/*', File::FNM_DOTMATCH, base: __dir__)
 
-	spec.required_ruby_version = ">= 2.5.0"
+	spec.required_ruby_version = ">= 3.1.0"
 
 	spec.add_dependency "console", "~> 1.10"
-	spec.add_dependency "nio4r", "~> 2.3"
+
+	spec.add_dependency "event"
 	spec.add_dependency "timers", "~> 4.1"
 
 	spec.add_development_dependency "async-rspec", "~> 1.1"

examples/fibers.rb

@@ -50,7 +50,7 @@ def timeout(duration)
 
 		timer = reactor.add_timer(duration) do
 			if self.alive?
-				error = Fiber::TimeoutError.new("execution expired")
+				error = Fiber::TimeoutError.new
 				error.set_backtrace backtrace
 				self.resume error
 			end

gems.rb

@@ -4,6 +4,9 @@
 
 gemspec
 
+# gem "event", path: "../event"
+# gem "async-rspec", path: "../async-rspec"
+
 group :maintenance, optional: true do
 	gem "bake-bundler"
 	gem "bake-modernize"

lib/async.rb

@@ -21,15 +21,14 @@
 # THE SOFTWARE.
 
 require_relative "async/version"
-require_relative "async/logger"
 require_relative "async/reactor"
 
 require_relative "kernel/async"
 require_relative "kernel/sync"
 
 module Async
 	# Invoke `Reactor.run` with all arguments/block.
-	def self.run(*arguments, &block)
-		Reactor.run(*arguments, &block)
+	def self.run(...)
+		Reactor.run(...)
 	end
 end

lib/async/condition.rb

@@ -37,11 +37,9 @@ def wait
 			fiber = Fiber.current
 			@waiting << fiber
 
-			Task.yield
-
-			# It would be nice if there was a better construct for this. We only need to invoke #delete if the task was not resumed normally. This can only occur with `raise` and `throw`. But there is no easy way to detect this.
-		# ensure when not return or ensure when raise, throw
+			Fiber.scheduler.transfer
 		rescue Exception
+			# It would be nice if there was a better construct for this. We only need to invoke #delete if the task was not resumed normally. This can only occur with `raise` and `throw`. But there is no easy way to detect this.
 			@waiting.delete(fiber)
 			raise
 		end
@@ -61,7 +59,7 @@ def signal(value = nil)
 			@waiting = []
 
 			waiting.each do |fiber|
-				fiber.resume(value) if fiber.alive?
+				Fiber.scheduler.resume(fiber, value) if fiber.alive?
 			end
 
 			return nil

lib/async/debug/selector.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-# Copyright, 2018, by Samuel G. D. Williams. <http://www.codeotaku.com>
+# Copyright, 2021, by Samuel G. D. Williams. <http://www.codeotaku.com>
 # 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -20,62 +20,14 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-require_relative 'monitor'
-require_relative '../logger'
-
-require 'nio'
-require 'set'
+require 'fiber'
+require 'event/debug/selector'
 
 module Async
 	module Debug
-		class LeakError < RuntimeError
-			def initialize(monitors)
-				super "Trying to close selector with active monitors: #{monitors.inspect}! This may cause your socket or file descriptor to leak."
-			end
-		end
-
-		class Selector
-			def initialize(selector = NIO::Selector.new)
-				@selector = selector
-				@monitors = Set.new
-			end
-
-			def register(object, interests)
-				Async.logger.debug(self) {"Registering #{object.inspect} for #{interests}."}
-
-				unless io = ::IO.try_convert(object)
-					raise RuntimeError, "Could not convert #{io} into IO!"
-				end
-
-				monitor = Monitor.new(@selector.register(object, interests), self)
-
-				@monitors.add(monitor)
-
-				return monitor
-			end
-
-			def deregister(monitor)
-				Async.logger.debug(self) {"Deregistering #{monitor.inspect}."}
-
-				unless @monitors.delete?(monitor)
-					raise RuntimeError, "Trying to remove monitor for #{monitor.inspect} but it was not registered!"
-				end
-			end
-
-			def wakeup
-				@selector.wakeup
-			end
-
-			def close
-				if @monitors.any?
-					raise LeakError, @monitors
-				end
-			ensure
-				@selector.close
-			end
-
-			def select(*arguments)
-				@selector.select(*arguments)
+		class Selector < Event::Debug::Selector
+			def initialize(selector = nil)
+				super(selector || Event::Backend.new(Fiber.current))
 			end
 		end
 	end

lib/async/debug/monitor.rb → lib/async/interrupt.rb

@@ -1,6 +1,4 @@
-# frozen_string_literal: true
-
-# Copyright, 2018, by Samuel G. D. Williams. <http://www.codeotaku.com>
+# Copyright, 2020, by Samuel G. D. Williams. <http://www.codeotaku.com>
 # 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -20,28 +18,33 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-require 'delegate'
-
 module Async
-	module Debug
-		class Monitor < Delegator
-			def initialize(monitor, selector)
-				@monitor = monitor
-				@selector = selector
-			end
-
-			def __getobj__
-				@monitor
-			end
+	# A thread safe synchronisation primative.
+	class Interrupt
+		def initialize(scheduler, &block)
+			@scheduler = scheduler
+			@input, @output = IO.pipe
 
-			def close
-				@selector.deregister(self)
-				@monitor.close
+			@fiber = Fiber.new do
+				while true
+					@scheduler.io_wait(@fiber, @input, ::Event::READABLE)
+					block.call(@input.read_nonblock(1))
+				end
 			end
 
-			def inspect
-				"\#<#{self.class} io=#{@monitor.io.inspect} interests=#{@monitor.interests.inspect} readiness=#{@monitor.readiness.inspect}>"
-			end
+			@fiber.transfer
+		end
+
+		def signal(event = '.')
+			@output.write('.')
+			@output.flush
+		end
+
+		def close
+			@input.close
+			@output.close
 		end
 	end
+
+	private_constant :Interrupt
 end

lib/async/node.rb

@@ -175,6 +175,10 @@ def initialize(parent = nil, annotation: nil, transient: false)
 			end
 		end
 
+		def root
+			@parent&.root || self
+		end
+
 		# You should not directly rely on these pointers but instead use `#children`.
 		# List pointers:
 		attr_accessor :head
@@ -225,7 +229,7 @@ def backtrace(*arguments)
 		end
 
 		def to_s
-			"\#<#{description}>"
+			"\#<#{self.description}>"
 		end
 
 		# Change the parent of this node.
@@ -329,6 +333,10 @@ def stop(later = false)
 			end
 		end
 
+		def stopped?
+			@children.nil?
+		end
+
 		def print_hierarchy(out = $stdout, backtrace: true)
 			self.traverse do |node, level|
 				indent = "\t" * level

lib/async/notification.rb

@@ -30,7 +30,7 @@ class Notification < Condition
 		def signal(value = nil, task: Task.current)
 			return if @waiting.empty?
 
-			task.reactor << Signal.new(@waiting, value)
+			Fiber.scheduler << Signal.new(@waiting, value)
 
 			@waiting = []
 
@@ -42,9 +42,9 @@ def alive?
 				true
 			end
 
-			def resume
+			def transfer
 				waiting.each do |fiber|
-					fiber.resume(value) if fiber.alive?
+					fiber.transfer(value) if fiber.alive?
 				end
 			end
 		end