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task.rb
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task.rb
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# Copyright, 2017, by Samuel G. D. Williams. <http://www.codeotaku.com>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
require 'fiber'
require 'forwardable'
require_relative 'node'
require_relative 'condition'
module Async
# Raised when a task is explicitly stopped.
class Stop < Exception
end
# A task represents the state associated with the execution of an asynchronous
# block.
class Task < Node
extend Forwardable
# Yield the unerlying `result` for the task. If the result
# is an Exception, then that result will be raised an its
# exception.
# @return [Object] result of the task
# @raise [Exception] if the result is an exception
# @yield [result] result of the task if a block if given.
def self.yield
if block_given?
result = yield
else
result = Fiber.yield
end
if result.is_a? Exception
raise result
else
return result
end
end
# Create a new task.
# @param reactor [Async::Reactor] the reactor this task will run within.
# @param parent [Async::Task] the parent task.
def initialize(reactor, parent = Task.current?)
super(parent || reactor)
@reactor = reactor
@status = :initialized
@result = nil
@finished = nil
@fiber = Fiber.new do |*args|
set!
begin
@result = yield(self, *args)
@status = :complete
# Async.logger.debug("Task #{self} completed normally.")
rescue Stop
@status = :stop
# Async.logger.debug("Task #{self} stopped: #{$!}")
Async.logger.debug(self) {$!}
rescue Exception => error
@result = error
@status = :failed
Async.logger.debug(self) {$!}
raise
ensure
# Async.logger.debug("Task #{self} closing: #{$!}")
finish!
end
end
end
def to_s
"<#{self.description} status=#{@status}>"
end
# @attr ios [Reactor] The reactor the task was created within.
attr :reactor
def_delegators :@reactor, :timeout, :sleep
# Yield back to the reactor and allow other fibers to execute.
def yield
reactor.yield
end
# @attr fiber [Fiber] The fiber which is being used for the execution of this task.
attr :fiber
def_delegators :@fiber, :alive?
# @attr status [Symbol] The status of the execution of the fiber, one of `:running`, `:complete`, `:stopped`, or `:failed`.
attr :status
# Resume the execution of the task.
def run(*args)
if @status == :initialized
@status = :running
@fiber.resume(*args)
else
raise RuntimeError, "Task already running!"
end
end
def async(*args, &block)
task = Task.new(@reactor, self, &block)
task.run(*args)
return task
end
# Retrieve the current result of the task. Will cause the caller to wait until result is available.
# @raise [RuntimeError] if the task's fiber is the current fiber.
# @return [Object]
def result
raise RuntimeError.new("Cannot wait on own fiber") if Fiber.current.equal?(@fiber)
if running?
@finished ||= Condition.new
@finished.wait
else
Task.yield {@result}
end
end
alias wait result
# Stop the task and all of its children.
# @return [void]
def stop
@children.each(&:stop)
if @fiber.alive?
@fiber.resume(Stop.new)
end
end
# Lookup the {Task} for the current fiber. Raise `RuntimeError` if none is available.
# @return [Async::Task]
# @raise [RuntimeError] if task was not {set!} for the current fiber.
def self.current
Thread.current[:async_task] or raise RuntimeError, "No async task available!"
end
# Check if there is a task defined for the current fiber.
# @return [Async::Task, nil]
def self.current?
Thread.current[:async_task]
end
# Check if the task is running.
# @return [Boolean]
def running?
@status == :running
end
# Whether we can remove this node from the reactor graph.
# @return [Boolean]
def finished?
super && @status != :running
end
private
# Finish the current task, and all bound bound IO objects.
def finish!
# 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(@result)
end
end
# Set the current fiber's `:async_task` to this task.
def set!
# This is actually fiber-local:
Thread.current[:async_task] = self
end
end
end