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

Defined Under Namespace

Classes: ClosedError

Instance Attribute Summary

Attributes inherited from Node

#A useful identifier for the current node., #Optional list of children., #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, #stopped?, #transient=, #transient?, #traverse

Constructor Details

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

Create a new scheduler.



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# File 'lib/async/scheduler.rb', line 40

def initialize(parent = nil, selector: nil)
	super(parent)
	
	@selector = selector || ::IO::Event::Selector.new(Fiber.current)
	@interrupted = false
	
	@blocked = 0
	
	@busy_time = 0.0
	@idle_time = 0.0
	
	@timers = ::IO::Event::Timers.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 31

def self.supported?
	true
end

Instance Method Details

#address_resolve(hostname) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 214

def address_resolve(hostname)
	# On some platforms, hostnames may contain a device-specific suffix (e.g. %en0). We need to strip this before resolving.
	# See <https://github.com/socketry/async/issues/180> for more details.
	hostname = hostname.split("%", 2).first
	::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 423

def async(*arguments, **options, &block)
	Kernel.raise ClosedError if @selector.nil?
	
	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.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 171

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

Terminate all child tasks and close the scheduler.



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# File 'lib/async/scheduler.rb', line 99

def close
	self.run_loop do
		until self.terminate
			self.run_once!
		end
	end
	
	Kernel.raise "Closing scheduler with blocked operations!" if @blocked > 0
ensure
	# We want `@selector = nil` to be a visible side effect from this point forward, specifically in `#interrupt` and `#unblock`. If the selector is closed, then we don't want to push any fibers to it.
	selector = @selector
	@selector = nil
	
	selector&.close
	
	consume
end

#closed? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/async/scheduler.rb', line 119

def closed?
	@selector.nil?
end

#fiber ⇒ Object 



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# File 'lib/async/scheduler.rb', line 441

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 130

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 254

def io_read(io, buffer, length, offset = 0)
	fiber = Fiber.current
	
	if timeout = get_timeout(io)
		timer = @timers.after(timeout) do
			fiber.raise(::IO::TimeoutError, "Timeout (#{timeout}s) while waiting for IO to become readable!")
		end
	end
	
	@selector.io_read(fiber, io, buffer, length, offset)
ensure
	timer&.cancel!
end

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



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# File 'lib/async/scheduler.rb', line 233

def io_wait(io, events, timeout = nil)
	fiber = Fiber.current
	
	if timeout
		# If an explicit timeout is specified, we expect that the user will handle it themselves:
		timer = @timers.after(timeout) do
			fiber.transfer
		end
	elsif timeout = get_timeout(io)
		# Otherwise, if we default to the io's timeout, we raise an exception:
		timer = @timers.after(timeout) do
			fiber.raise(::IO::TimeoutError, "Timeout (#{timeout}s) while waiting for IO to become ready!")
		end
	end
	
	return @selector.io_wait(fiber, io, events)
ensure
	timer&.cancel!
end

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



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# File 'lib/async/scheduler.rb', line 269

def io_write(io, buffer, length, offset = 0)
	fiber = Fiber.current
	
	if timeout = get_timeout(io)
		timer = @timers.after(timeout) do
			fiber.raise(::IO::TimeoutError, "Timeout (#{timeout}s) while waiting for IO to become writable!")
		end
	end
	
	@selector.io_write(fiber, io, buffer, length, offset)
ensure
	timer&.cancel!
end

#kernel_sleep(duration = nil) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 205

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

#load ⇒ Object

Compute the scheduler load according to the busy and idle times that are updated by the run loop.



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# File 'lib/async/scheduler.rb', line 56

def load
	total_time = @busy_time + @idle_time
	
	# If the total time is zero, then the load is zero:
	return 0.0 if total_time.zero?
	
	# We normalize to a 1 second window:
	if total_time > 1.0
		ratio = 1.0 / total_time
		@busy_time *= ratio
		@idle_time *= ratio
		
		# We don't need to divide here as we've already normalised it to a 1s window:
		return @busy_time
	else
		return @busy_time / total_time
	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 290

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 147

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

#raise ⇒ Object

Raise an exception on a specified fiber with the given arguments.

This internally schedules the current fiber to be ready, before raising the exception, so that it will later resume execution.



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# File 'lib/async/scheduler.rb', line 157

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

#resume(fiber, *arguments) ⇒ Object

Resume execution of the specified fiber.



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# File 'lib/async/scheduler.rb', line 165

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 402

def run(...)
	Kernel.raise ClosedError if @selector.nil?
	
	initial_task = self.async(...) if block_given?
	
	self.run_loop do
		run_once
	end
	
	return initial_task
end

#run_once(timeout = nil) ⇒ Object

Run one iteration of the event loop. Does not handle interrupts.



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# File 'lib/async/scheduler.rb', line 341

def run_once(timeout = nil)
	Kernel.raise "Running scheduler on non-blocking fiber!" unless Fiber.blocking?
	
	if self.finished?
		self.stop
	end
	
	# If we are finished, we stop the task tree and exit:
	if @children.nil?
		return false
	end
	
	return run_once!(timeout)
end

#scheduler_close(error = $!) ⇒ Object

Invoked when the fiber scheduler is being closed.

Executes the run loop until all tasks are finished, then closes the scheduler.



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

def scheduler_close(error = $!)
	# If the execution context (thread) was handling an exception, we want to exit as quickly as possible:
	unless error
		self.run
	end
ensure
	self.close
end

#stop ⇒ Object

Stop all children, including transient children, ignoring any signals.



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# File 'lib/async/scheduler.rb', line 372

def stop
	@children&.each do |child|
		child.stop
	end
end

#terminate ⇒ Object

Terminate all child tasks.



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# File 'lib/async/scheduler.rb', line 88

def terminate
	# If that doesn't work, take more serious action:
	@children&.each do |child|
		child.terminate
	end
	
	return @children.nil?
end

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



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# File 'lib/async/scheduler.rb', line 461

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 124

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 136

def transfer
	@selector.transfer
end

#unblock(blocker, fiber) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 194

def unblock(blocker, fiber)
	# $stderr.puts "unblock(#{blocker}, #{fiber})"
	
	# This operation is protected by the GVL:
	if selector = @selector
		selector.push(fiber)
		selector.wakeup
	end
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 447

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!
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 141

def yield
	@selector.yield
end