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

Constant Summary collapse

WORKER_POOL = 
ENV.fetch("ASYNC_SCHEDULER_WORKER_POOL", nil).then do |value|
	value == "true" ? true : nil
end

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, profiler: Profiler&.default, worker_pool: WORKER_POOL) ⇒ Scheduler

Create a new scheduler.

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# File 'lib/async/scheduler.rb', line 53

def initialize(parent = nil, selector: nil, profiler: Profiler&.default, worker_pool: WORKER_POOL)
	super(parent)
	
	@selector = selector || ::IO::Event::Selector.new(Fiber.current)
	@profiler = profiler
	
	@interrupted = false
	
	@blocked = 0
	
	@busy_time = 0.0
	@idle_time = 0.0
	
	@timers = ::IO::Event::Timers.new
	if worker_pool == true
		@worker_pool = WorkerPool.new
	else
		@worker_pool = worker_pool
	end
	
	if @worker_pool
		self.singleton_class.prepend(WorkerPool::BlockingOperationWait)
	end
end

Class Method Details

.supported? ⇒ Boolean

Whether the fiber scheduler is supported.

Returns:

  • (Boolean)
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# File 'lib/async/scheduler.rb', line 44

def self.supported?
	true
end

Instance Method Details

#address_resolve(hostname) ⇒ Object

Resolve the address of the given hostname.

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# File 'lib/async/scheduler.rb', line 265

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.

Use #run or Task#async instead.

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.

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# File 'lib/async/scheduler.rb', line 528

def async(*arguments, **options, &block)
	# warn "Async::Scheduler#async is deprecated. Use `run` or `Task#async` instead.", uplevel: 1, category: :deprecated
	
	Kernel.raise ClosedError if @selector.nil?
	
	task = Task.new(Task.current? || self, **options, &block)
	
	task.run(*arguments)
	
	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 206

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 124

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
	
	worker_pool = @worker_pool
	@worker_pool = nil
	
	worker_pool&.close
	
	consume
end

#closed? ⇒ Boolean

Returns:

  • (Boolean)
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# File 'lib/async/scheduler.rb', line 149

def closed?
	@selector.nil?
end

#fiber ⇒ Object

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# File 'lib/async/scheduler.rb', line 540

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 160

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

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

Read from the specified IO into the buffer.

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# File 'lib/async/scheduler.rb', line 320

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

Wait for the specified IO to become ready for the specified events.

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# File 'lib/async/scheduler.rb', line 290

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

Write the specified buffer to the IO.

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# File 'lib/async/scheduler.rb', line 344

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

Sleep for the specified duration.

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# File 'lib/async/scheduler.rb', line 251

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 81

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 369

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 177

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 187

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 195

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.

Forwards all parameters to #async if a block is given.

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# File 'lib/async/scheduler.rb', line 502

def run(...)
	Kernel.raise ClosedError if @selector.nil?
	
	begin
		@profiler&.start
		
		initial_task = self.async(...) if block_given?
		
		self.run_loop do
			run_once
		end
		
		return initial_task
	ensure
		@profiler&.stop
	end
end

#run_once(timeout = nil) ⇒ Object

Run one iteration of the event loop.

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# File 'lib/async/scheduler.rb', line 423

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 103

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.

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# File 'lib/async/scheduler.rb', line 457

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 113

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

Invoke the block, but after the specified timeout, raise the specified exception with the given message. 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 576

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 154

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 166

def transfer
	@selector.transfer
end

#unblock(blocker, fiber) ⇒ Object

Unblock a fiber that was previously blocked.

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# File 'lib/async/scheduler.rb', line 235

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 553

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 171

def yield
	@selector.yield
end