AsyncSourceAsyncScheduler

class Scheduler

Handles scheduling of fibers. Implements the fiber scheduler interface.

Nested

Definitions

def self.supported?

  • public

Whether the fiber scheduler is supported.

Signature

public

Since stable-v1.

Implementation

def self.supported?
	true
end

def initialize(parent = nil, selector: nil)

  • public

Create a new scheduler.

Signature

public

Since stable-v1.

parameter parent Node | Nil

The parent node to use for task hierarchy.

parameter selector IO::Event::Selector

The selector to use for event handling.

Implementation

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

def load

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

Signature

returns Float

The load of the scheduler. 0.0 means no load, 1.0 means fully loaded or over-loaded.

Implementation

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

def scheduler_close(error = $!)

Invoked when the fiber scheduler is being closed.

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

Implementation

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

def terminate

Terminate all child tasks.

Implementation

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

def close

  • public

Terminate all child tasks and close the scheduler.

Signature

public

Since stable-v1.

Implementation

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

def closed?

  • public

Signature

returns Boolean

Whether the scheduler has been closed.

public

Since stable-v1.

Implementation

def closed?
	@selector.nil?
end

def to_s

Signature

returns String

A description of the scheduler.

Implementation

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

def interrupt

  • asynchronous

Interrupt the event loop and cause it to exit.

Signature

asynchronous

May be called from any thread.

Implementation

def interrupt
	@interrupted = true
	@selector&.wakeup
end

def transfer

Transfer from the calling fiber to the event loop.

Implementation

def transfer
	@selector.transfer
end

def yield

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

Implementation

def yield
	@selector.yield
end

def push(fiber)

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

Signature

parameter fiber Fiber | Object

The object to be resumed on the next iteration of the run-loop.

Implementation

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

def raise(...)

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.

Signature

parameter fiber Fiber

The fiber to raise the exception on.

parameter *arguments Array

The arguments to pass to the fiber.

Implementation

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

def resume(fiber, *arguments)

Resume execution of the specified fiber.

Signature

parameter fiber Fiber

The fiber to resume.

parameter arguments Array

The arguments to pass to the fiber.

Implementation

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

def block(blocker, timeout)

  • asynchronous

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

Signature

asynchronous

May only be called on same thread as fiber scheduler.

Implementation

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

def unblock(blocker, fiber)

  • asynchronous

Signature

asynchronous

May be called from any thread.

Implementation

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

def kernel_sleep(duration = nil)

  • asynchronous

Signature

asynchronous

May be non-blocking..

Implementation

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

def address_resolve(hostname)

  • asynchronous

Signature

asynchronous

May be non-blocking..

Implementation

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

def io_wait(io, events, timeout = nil)

  • asynchronous

Signature

asynchronous

May be non-blocking..

Implementation

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

def process_wait(pid, flags)

  • asynchronous

Wait for the specified process ID to exit.

Signature

parameter pid Integer

The process ID to wait for.

parameter flags Integer

A bit-mask of flags suitable for Process::Status.wait.

returns Process::Status

A process status instance.

asynchronous

May be non-blocking..

Implementation

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

def run_once(timeout = nil)

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

Signature

parameter timeout Float | Nil

The maximum timeout, or if nil, indefinite.

returns Boolean

Whether there is more work to do.

Implementation

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

def stop

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

Implementation

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

def run(...)

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

Implementation

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

def async(*arguments, **options, &block)

  • deprecated

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.

Signature

yields {|task| ...}

Executed within the task.

returns Task

The task that was scheduled into the reactor.

deprecated

With no replacement.

Implementation

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

def with_timeout(duration, exception = TimeoutError, message = "execution expired", &block)

Invoke the block, but after the specified timeout, raise class Async::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.

Signature

parameter duration Numeric

The time in seconds, in which the task should complete.

Implementation

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

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