class Async::Task

@public Since ‘stable-v1`.

def self.current

@raises[RuntimeError] If task was not {set!} for the current fiber.
@returns [Task]
Lookup the {Task} for the current fiber. Raise `RuntimeError` if none is available.
def self.current
	Fiber.current.async_task or raise RuntimeError, "No async task available!"
end

def self.current?

@returns [Interface(:async) | Nil]
Check if there is a task defined for the current fiber.
def self.current?
	Fiber.current.async_task
end

def self.yield

Deprecated:
  • With no replacement.
def self.yield
	Fiber.scheduler.transfer
end

def alive?

@returns [Boolean] Whether the internal fiber is alive, i.e. it is actively executing.
def alive?
	@fiber&.alive?
end

def annotate(annotation, &block)

@parameter annotation [String] The description to annotate the task with.

This will internally try to annotate the fiber if it is running, otherwise it will annotate the task itself.

Annotate the task with a description.
def annotate(annotation, &block)
	if @fiber
		@fiber.annotate(annotation, &block)
	else
		super
	end
end

def annotation

@returns [Object] The annotation of the task.
def annotation
	if @fiber
		@fiber.annotation
	else
		super
	end
end

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

@returns [Task] The child task.
@raises [FinishedError] If the task has already finished.

Run an asynchronous task as a child of the current task.
def async(*arguments, **options, &block)
	raise FinishedError if self.finished?
	
	task = Task.new(self, **options, &block)
	
	task.run(*arguments)
	
	return task
end

def backtrace(*arguments)

@returns [Array(Thread::Backtrace::Location) | Nil] The backtrace of the task, if available.
def backtrace(*arguments)
	@fiber&.backtrace(*arguments)
end

def completed!(result)

State transition into the completed state.
def completed!(result)
	@result = result
	@status = :completed
end

def completed?

@returns [Boolean] Whether the task has completed execution and generated a result.
def completed?
	@status == :completed
end

def current?

@returns [Boolean] Whether this task is the currently executing task.
def current?
	Fiber.current.equal?(@fiber)
end

def defer_stop

@public Since `stable-v1`.
@yields {} The block of code to execute.

If stop is invoked a second time, it will be immediately executed.

You can nest calls to defer_stop, but the stop will only be deferred until the outermost block exits.

Defer the handling of stop. During the execution of the given block, if a stop is requested, it will be deferred until the block exits. This is useful for ensuring graceful shutdown of servers and other long-running tasks. You should wrap the response handling code in a defer_stop block to ensure that the task is stopped when the response is complete but not before.
def defer_stop
	# Tri-state variable for controlling stop:
	# - nil: defer_stop has not been called.
	# - false: defer_stop has been called and we are not stopping.
	# - true: defer_stop has been called and we will stop when exiting the block.
	if @defer_stop.nil?
		# If we are not deferring stop already, we can defer it now:
		@defer_stop = false
		
		begin
			yield
		rescue Stop
			# If we are exiting due to a stop, we shouldn't try to invoke stop again:
			@defer_stop = nil
			raise
		ensure
			# If we were asked to stop, we should do so now:
			if @defer_stop
				@defer_stop = nil
				raise Stop, "Stopping current task (was deferred)!"
			end
		end
	else
		# If we are deferring stop already, entering it again is a no-op.
		yield
	end
end

def failed!(exception = false)

State transition into the failed state.
def failed!(exception = false)
	@result = exception
	@status = :failed
end

def failed?

@returns [Boolean] Whether the task failed with an exception.
def failed?
	@status == :failed
end

def finish!

Finish the current task, moving any children to the parent.
def finish!
	# Don't hold references to the fiber or block after the task has finished:
	@fiber = nil
	@block = nil # If some how we went directly from initialized to finished.
	
	# Attempt to remove this node from the task tree.
	consume
	
	# If this task was being used as a future, signal completion here:
	if @finished
		@finished.signal(self)
		@finished = nil
	end
end

def finished?

@returns [Boolean]
Whether we can remove this node from the reactor graph.
def finished?
	# If the block is nil and the fiber is nil, it means the task has finished execution. This becomes true after `finish!` is called.
	super && @block.nil? && @fiber.nil?
end

def initialize(parent = Task.current?, finished: nil, **options, &block)

@parameter parent [Task] the parent task.
@parameter reactor [Reactor] the reactor this task will run within.
Create a new task.
def initialize(parent = Task.current?, finished: nil, **options, &block)
	super(parent, **options)
	
	# These instance variables are critical to the state of the task.
	# In the initialized state, the @block should be set, but the @fiber should be nil.
	# In the running state, the @fiber should be set.
	# In a finished state, the @block should be nil, and the @fiber should be nil.
	@block = block
	@fiber = nil
	
	@status = :initialized
	@result = nil
	@finished = finished
	
	@defer_stop = nil
end

def reactor

@returns [Scheduler] The scheduler for this task.
def reactor
	self.root
end

def run(*arguments)

@raises [RuntimeError] If the task is already running.

Begin the execution of the task.
def run(*arguments)
	if @status == :initialized
		@status = :running
		
		schedule do
			@block.call(self, *arguments)
		rescue => error
			# I'm not completely happy with this overhead, but the alternative is to not log anything which makes debugging extremely difficult. Maybe we can introduce a debug wrapper which adds extra logging.
			if @finished.nil?
				Console::Event::Failure.for(error).emit(self, "Task may have ended with unhandled exception.", severity: :warn)
			# else
			# 	Console::Event::Failure.for(error).emit(self, severity: :debug)
			end
			
			raise
		end
	else
		raise RuntimeError, "Task already running!"
	end
end

def running?

@returns [Boolean] Whether the task is running.
def running?
	@status == :running
end

def schedule(&block)

def schedule(&block)
	@fiber = Fiber.new(annotation: self.annotation) do
		begin
			completed!(yield)
		rescue Stop
			stopped!
		rescue StandardError => error
			failed!(error)
		rescue Exception => exception
			failed!(exception)
			
			# This is a critical failure, we should stop the reactor:
			raise
		ensure
			# Console.info(self) {"Task ensure $! = #{$!} with #{@children&.size.inspect} children!"}
			finish!
		end
	end
	
	@fiber.async_task = self
	
	self.root.resume(@fiber)
end

def sleep(duration = nil)

Deprecated:
  • Prefer {Kernel#sleep} except when compatibility with `stable-v1` is required.
def sleep(duration = nil)
	super
end

def stop(later = false)

@parameter later [Boolean] Whether to stop the task later, or immediately.

If `later` is false, it means that `stop` has been invoked directly. When `later` is true, it means that `stop` is invoked by `stop_children` or some other indirect mechanism. In that case, if we encounter the "current" fiber, we can't stop it right away, as it's currently performing `#stop`. Stopping it immediately would interrupt the current stop traversal, so we need to schedule the stop to occur later.

Stop the task and all of its children.
def stop(later = false)
	if self.stopped?
		# If the task is already stopped, a `stop` state transition re-enters the same state which is a no-op. However, we will also attempt to stop any running children too. This can happen if the children did not stop correctly the first time around. Doing this should probably be considered a bug, but it's better to be safe than sorry.
		return stopped!
	end
	
	# If we are deferring stop...
	if @defer_stop == false
		# Don't stop now... but update the state so we know we need to stop later.
		@defer_stop = true
		return false
	end
	
	# If the fiber is alive, we need to stop it:
	if @fiber&.alive?
		if self.current?
			# If the fiber is current, and later is `true`, we need to schedule the fiber to be stopped later, as it's currently invoking `stop`:
			if later
				# If the fiber is the current fiber and we want to stop it later, schedule it:
				Fiber.scheduler.push(Stop::Later.new(self))
			else
				# Otherwise, raise the exception directly:
				raise Stop, "Stopping current task!"
			end
		else
			# If the fiber is not curent, we can raise the exception directly:
			begin
				# There is a chance that this will stop the fiber that originally called stop. If that happens, the exception handling in `#stopped` will rescue the exception and re-raise it later.
				Fiber.scheduler.raise(@fiber, Stop)
			rescue FiberError
				# In some cases, this can cause a FiberError (it might be resumed already), so we schedule it to be stopped later:
				Fiber.scheduler.push(Stop::Later.new(self))
			end
		end
	else
		# We are not running, but children might be, so transition directly into stopped state:
		stop!
	end
end

def stop!

def stop!
	stopped!
	
	finish!
end

def stopped!

def stopped!
	# Console.info(self, status:) {"Task #{self} was stopped with #{@children&.size.inspect} children!"}
	@status = :stopped
	
	stopped = false
	
	begin
		# We are not running, but children might be so we should stop them:
		stop_children(true)
	rescue Stop
		stopped = true
		# If we are stopping children, and one of them tries to stop the current task, we should ignore it. We will be stopped later.
		retry
	end
	
	if stopped
		raise Stop, "Stopping current task!"
	end
end

def stopped?

@returns [Boolean] Whether the task has been stopped.
def stopped?
	@status == :stopped
end

def to_s

@returns [String] A description of the task and it's current status.
def to_s
	"\#<#{self.description} (#{@status})>"
end

def wait

@returns [Object] The final expression/result of the task's block.
@raises [RuntimeError] If the task's fiber is the current fiber.

Conceptually speaking, waiting on a task should return a result, and if it throws an exception, this is certainly an exceptional case that should represent a failure in your program, not an expected outcome. In other words, you should not design your programs to expect exceptions from `#wait` as a normal flow control, and prefer to catch known exceptions within the task itself and return a result that captures the intention of the failure, e.g. a `TimeoutError` might simply return `nil` or `false` to indicate that the operation did not generate a valid result (as a timeout was an expected outcome of the internal operation in this case).

Retrieve the current result of the task. Will cause the caller to wait until result is available. If the task resulted in an unhandled error (derived from `StandardError`), this will be raised. If the task was stopped, this will return `nil`.
def wait
	raise "Cannot wait on own fiber!" if Fiber.current.equal?(@fiber)
	
	# `finish!` will set both of these to nil before signaling the condition:
	if @block || @fiber
		@finished ||= Condition.new
		@finished.wait
	end
	
	if @status == :failed
		raise @result
	else
		return @result
	end
end

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

Execute the given block of code, raising the specified exception if it exceeds the given duration during a non-blocking operation.
def with_timeout(duration, exception = TimeoutError, message = "execution expired", &block)
	Fiber.scheduler.with_timeout(duration, exception, message, &block)
end

def yield

Yield back to the reactor and allow other fibers to execute.
def yield
	Fiber.scheduler.yield
end