Class: Async::Scheduler

Inherits:
Node
  • Object
show all
Defined in:
lib/async/scheduler.rb

Overview

Handles scheduling of fibers. Implements the fiber scheduler interface.

Direct Known Subclasses

Reactor

Instance Attribute Summary

Attributes inherited from Node

#annotation, #children, #head, #parent, #tail

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Node

#The parent node.=, #annotate, #backtrace, #children?, #consume, #description, #finished?, #print_hierarchy, #root, #stop, #stopped?, #terminate, #transient?, #traverse

Constructor Details

#initialize(parent = nil, selector: nil) ⇒ Scheduler

Returns a new instance of Scheduler.



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# File 'lib/async/scheduler.rb', line 26

def initialize(parent = nil, selector: nil)
	super(parent)
	
	@selector = selector || ::IO::Event::Selector.new(Fiber.current)
	@interrupted = false
	
	@blocked = 0
	
	@timers = ::Timers::Group.new
end

Class Method Details

.supported? ⇒ Boolean

Whether the fiber scheduler is supported.

Returns:

  • (Boolean) 


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# File 'lib/async/scheduler.rb', line 22

def self.supported?
	true
end

Instance Method Details

#address_resolve(hostname) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 144

def address_resolve(hostname)
	::Resolv.getaddresses(hostname)
end

#async(*arguments, **options, &block) ⇒ Object

Deprecated.

With no replacement.

Start an asynchronous task within the specified reactor. The task will be executed until the first blocking call, at which point it will yield and and this method will return.

This is the main entry point for scheduling asynchronus tasks.



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# File 'lib/async/scheduler.rb', line 252

def async(*arguments, **options, &block)
	task = Task.new(Task.current? || self, **options, &block)
	
	# I want to take a moment to explain the logic of this.
	# When calling an async block, we deterministically execute it until the
	# first blocking operation. We don't *have* to do this - we could schedule
	# it for later execution, but it's useful to:
	# - Fail at the point of the method call where possible.
	# - Execute determinstically where possible.
	# - Avoid scheduler overhead if no blocking operation is performed.
	task.run(*arguments)
	
	# Console.logger.debug "Initial execution of task #{fiber} complete (#{result} -> #{fiber.alive?})..."
	return task
end

#block(blocker, timeout) ⇒ Object

Invoked when a fiber tries to perform a blocking operation which cannot continue. A corresponding call #unblock must be performed to allow this fiber to continue.



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# File 'lib/async/scheduler.rb', line 103

def block(blocker, timeout)
	# $stderr.puts "block(#{blocker}, #{Fiber.current}, #{timeout})"
	fiber = Fiber.current
	
	if timeout
		timer = @timers.after(timeout) do
			if fiber.alive?
				fiber.transfer(false)
			end
		end
	end
	
	begin
		@blocked += 1
		@selector.transfer
	ensure
		@blocked -= 1
	end
ensure
	timer&.cancel
end

#close ⇒ Object 



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# File 'lib/async/scheduler.rb', line 44

def close
	# This is a critical step. Because tasks could be stored as instance variables, and since the reactor is (probably) going out of scope, we need to ensure they are stopped. Otherwise, the tasks will belong to a reactor that will never run again and are not stopped.
	self.terminate
	
	Kernel::raise "Closing scheduler with blocked operations!" if @blocked > 0
	
	# We depend on GVL for consistency:
	# @guard.synchronize do
	
	@selector&.close
	@selector = nil
	
	# end
	
	consume
end

#closed? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/async/scheduler.rb', line 63

def closed?
	@selector.nil?
end

#fiber ⇒ Object 



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# File 'lib/async/scheduler.rb', line 268

def fiber(...)
	return async(...).fiber
end

#interrupt ⇒ Object

Interrupt the event loop and cause it to exit.



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# File 'lib/async/scheduler.rb', line 72

def interrupt
	@interrupted = true
	@selector.wakeup
end

#io_read(io, buffer, length, offset = 0) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 170

def io_read(io, buffer, length, offset = 0)
	@selector.io_read(Fiber.current, io, buffer, length, offset)
end

#io_wait(io, events, timeout = nil) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 149

def io_wait(io, events, timeout = nil)
	fiber = Fiber.current
	
	if timeout
		timer = @timers.after(timeout) do
			fiber.raise(TimeoutError)
		end
	end
	
	# Console.logger.info(self, "-> io_wait", fiber, io, events)
	events = @selector.io_wait(fiber, io, events)
	# Console.logger.info(self, "<- io_wait", fiber, io, events)
	
	return events
rescue TimeoutError
	return false
ensure
	timer&.cancel
end

#io_write(io, buffer, length, offset = 0) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 174

def io_write(io, buffer, length, offset = 0)
	@selector.io_write(Fiber.current, io, buffer, length, offset)
end

#kernel_sleep(duration = nil) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 135

def kernel_sleep(duration = nil)
	if duration
		self.block(nil, duration)
	else
		self.transfer
	end
end

#process_wait(pid, flags) ⇒ Object

Wait for the specified process ID to exit.



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# File 'lib/async/scheduler.rb', line 184

def process_wait(pid, flags)
	return @selector.process_wait(Fiber.current, pid, flags)
end

#push(fiber) ⇒ Object

Schedule a fiber (or equivalent object) to be resumed on the next loop through the reactor.



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# File 'lib/async/scheduler.rb', line 89

def push(fiber)
	@selector.push(fiber)
end

#raise(*arguments) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 93

def raise(*arguments)
	@selector.raise(*arguments)
end

#resume(fiber, *arguments) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 97

def resume(fiber, *arguments)
	@selector.resume(fiber, *arguments)
end

#run ⇒ Object

Run the reactor until all tasks are finished. Proxies arguments to #async immediately before entering the loop, if a block is provided.



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# File 'lib/async/scheduler.rb', line 225

def run(...)
	Kernel::raise RuntimeError, 'Reactor has been closed' if @selector.nil?
	
	initial_task = self.async(...) if block_given?
	
	@interrupted = false
	
	while self.run_once
		if @interrupted
			break
		end
	end
	
	return initial_task
ensure
	Console.logger.debug(self) {"Exiting run-loop because #{$! ? $! : 'finished'}."}
end

#run_once(timeout = nil) ⇒ Object

Run one iteration of the event loop.



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# File 'lib/async/scheduler.rb', line 191

def run_once(timeout = nil)
	Kernel::raise "Running scheduler on non-blocking fiber!" unless Fiber.blocking?
	
	# If we are finished, we stop the task tree and exit:
	if self.finished?
		return false
	end
	
	interval = @timers.wait_interval
	
	# If there is no interval to wait (thus no timers), and no tasks, we could be done:
	if interval.nil?
		# Allow the user to specify a maximum interval if we would otherwise be sleeping indefinitely:
		interval = timeout
	elsif interval < 0
		# We have timers ready to fire, don't sleep in the selctor:
		interval = 0
	elsif timeout and interval > timeout
		interval = timeout
	end
	
	begin
		@selector.select(interval)
	rescue Errno::EINTR
		# Ignore.
	end
	
	@timers.fire
	
	# The reactor still has work to do:
	return true
end

#scheduler_close ⇒ Object 



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# File 'lib/async/scheduler.rb', line 37

def scheduler_close
	self.run
ensure
	self.close
end

#timeout_after(duration, exception, message, &block) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 288

def timeout_after(duration, exception, message, &block)
	with_timeout(duration, exception, message) do |timer|
		yield duration
	end
end

#to_s ⇒ Object 



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# File 'lib/async/scheduler.rb', line 67

def to_s
	"\#<#{self.description} #{@children&.size || 0} children (#{stopped? ? 'stopped' : 'running'})>"
end

#transfer ⇒ Object

Transfer from the calling fiber to the event loop.



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# File 'lib/async/scheduler.rb', line 78

def transfer
	@selector.transfer
end

#unblock(blocker, fiber) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 126

def unblock(blocker, fiber)
	# $stderr.puts "unblock(#{blocker}, #{fiber})"
	
	# This operation is protected by the GVL:
	@selector.push(fiber)
	@selector.wakeup
end

#with_timeout(duration, exception = TimeoutError, message = "execution expired", &block) ⇒ Object

Invoke the block, but after the specified timeout, raise TimeoutError in any currenly blocking operation. If the block runs to completion before the timeout occurs or there are no non-blocking operations after the timeout expires, the code will complete without any exception.



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# File 'lib/async/scheduler.rb', line 274

def with_timeout(duration, exception = TimeoutError, message = "execution expired", &block)
	fiber = Fiber.current
	
	timer = @timers.after(duration) do
		if fiber.alive?
			fiber.raise(exception, message)
		end
	end
	
	yield timer
ensure
	timer.cancel if timer
end

#yield ⇒ Object

Yield the current fiber and resume it on the next iteration of the event loop.



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# File 'lib/async/scheduler.rb', line 83

def yield
	@selector.yield
end