Class: Async::Task

Inherits:
Node
  • Object
show all
Defined in:
lib/async/task.rb

Overview

Encapsulates the state of a running task and it’s result.

“‘mermaid stateDiagram-v2

*

–> Initialized

Initialized –> Running : Run

Running –> Completed : Return Value Running –> Failed : Exception

Completed –> [*] Failed –> [*]

Running –> Stopped : Stop Stopped –> [*] Completed –> Stopped : Stop Failed –> Stopped : Stop Initialized –> Stopped : Stop “‘

Defined Under Namespace

Classes: FinishedError

Instance Attribute Summary collapse

Attributes inherited from Node

#children, #head, #parent, #tail

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Node

#The parent node.=, #children?, #consume, #description, #print_hierarchy, #root, #terminate, #transient?, #traverse

Constructor Details

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

Create a new task.



76
77
78
79
80
81
82
83
84
85
86
87
88
89
 
# File 'lib/async/task.rb', line 76

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
end

Instance Attribute Details

#fiber ⇒ Object (readonly) 



135
136
137
 
# File 'lib/async/task.rb', line 135

def fiber
  @fiber
end

#result ⇒ Object (readonly)

Access the result of the task without waiting. May be nil if the task is not completed. Does not raise exceptions.



221
222
223
 
# File 'lib/async/task.rb', line 221

def result
  @result
end

#status ⇒ Object (readonly) 



172
173
174
 
# File 'lib/async/task.rb', line 172

def status
  @status
end

Class Method Details

.current ⇒ Object

Lookup the Async::Task for the current fiber. Raise ‘RuntimeError` if none is available. @raises If task was not #set! for the current fiber.



264
265
266
 
# File 'lib/async/task.rb', line 264

def self.current
	Thread.current[:async_task] or raise RuntimeError, "No async task available!"
end

.current? ⇒ Boolean

Check if there is a task defined for the current fiber.

Returns:

  • (Boolean) 


270
271
272
 
# File 'lib/async/task.rb', line 270

def self.current?
	Thread.current[:async_task]
end

.yield ⇒ Object

Deprecated.

With no replacement.



69
70
71
 
# File 'lib/async/task.rb', line 69

def self.yield
	Fiber.scheduler.transfer
end

Instance Method Details

#alive? ⇒ Boolean

Whether the internal fiber is alive, i.e. it

Returns:

  • (Boolean) 


138
139
140
 
# File 'lib/async/task.rb', line 138

def alive?
	@fiber&.alive?
end

#annotate(annotation, &block) ⇒ Object 



99
100
101
102
103
104
105
 
# File 'lib/async/task.rb', line 99

def annotate(annotation, &block)
	if @fiber
		@fiber.annotate(annotation, &block)
	else
		super
	end
end

#annotation ⇒ Object 



107
108
109
110
111
112
113
 
# File 'lib/async/task.rb', line 107

def annotation
	if @fiber
		@fiber.annotation
	else
		super
	end
end

#async(*arguments, **options, &block) ⇒ Object

Run an asynchronous task as a child of the current task.

Raises:



188
189
190
191
192
193
194
195
196
 
# File 'lib/async/task.rb', line 188

def async(*arguments, **options, &block)
	raise FinishedError if self.finished?
	
	task = Task.new(self, **options, &block)
	
	task.run(*arguments)
	
	return task
end

#backtrace(*arguments) ⇒ Object 



95
96
97
 
# File 'lib/async/task.rb', line 95

def backtrace(*arguments)
	@fiber&.backtrace(*arguments)
end

#completed? ⇒ Boolean Also known as: complete?

The task has completed execution and generated a result.

Returns:

  • (Boolean) 


165
166
167
 
# File 'lib/async/task.rb', line 165

def completed?
	@status == :completed
end

#current? ⇒ Boolean

Returns:

  • (Boolean) 


274
275
276
 
# File 'lib/async/task.rb', line 274

def current?
	Fiber.current.equal?(@fiber)
end

#failed? ⇒ Boolean

Returns:

  • (Boolean) 


155
156
157
 
# File 'lib/async/task.rb', line 155

def failed?
	@status == :failed
end

#finished? ⇒ Boolean

Whether we can remove this node from the reactor graph.

Returns:

  • (Boolean) 


144
145
146
147
 
# File 'lib/async/task.rb', line 144

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

#reactor ⇒ Object 



91
92
93
 
# File 'lib/async/task.rb', line 91

def reactor
	self.root
end

#run(*arguments) ⇒ Object

Begin the execution of the task.



175
176
177
178
179
180
181
182
183
184
185
 
# File 'lib/async/task.rb', line 175

def run(*arguments)
	if @status == :initialized
		@status = :running
		
		schedule do
			@block.call(self, *arguments)
		end
	else
		raise RuntimeError, "Task already running!"
	end
end

#running? ⇒ Boolean

Whether the task is running.

Returns:

  • (Boolean) 


151
152
153
 
# File 'lib/async/task.rb', line 151

def running?
	@status == :running
end

#sleep(duration = nil) ⇒ Object

Deprecated.

Prefer Kernel#sleep except when compatibility with ‘stable-v1` is required.



120
121
122
 
# File 'lib/async/task.rb', line 120

def sleep(duration = nil)
	super
end

#stop(later = false) ⇒ Object

Stop the task and all of its children.

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.



228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
 
# File 'lib/async/task.rb', line 228

def stop(later = false)
	if self.stopped?
		# If we already stopped this task... don't try to stop it again:
		return
	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

#stopped? ⇒ Boolean

The task has been stopped

Returns:

  • (Boolean) 


160
161
162
 
# File 'lib/async/task.rb', line 160

def stopped?
	@status == :stopped
end

#to_s ⇒ Object 



115
116
117
 
# File 'lib/async/task.rb', line 115

def to_s
	"\#<#{self.description} (#{@status})>"
end

#wait ⇒ Object

Retrieve the current result of the task. Will cause the caller to wait until result is available. If the result was an exception, raise that exception.

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).



204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
 
# File 'lib/async/task.rb', line 204

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 @result.is_a?(Exception)
		raise @result
	else
		return @result
	end
end

#with_timeout(duration, exception = TimeoutError, message = "execution expired", &block) ⇒ Object

Execute the given block of code, raising the specified exception if it exceeds the given duration during a non-blocking operation.



125
126
127
 
# File 'lib/async/task.rb', line 125

def with_timeout(duration, exception = TimeoutError, message = "execution expired", &block)
	Fiber.scheduler.with_timeout(duration, exception, message, &block)
end

#yield ⇒ Object

Yield back to the reactor and allow other fibers to execute.



130
131
132
 
# File 'lib/async/task.rb', line 130

def yield
	Fiber.scheduler.yield
end