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

Instance Attribute Summary

Attributes inherited from Node

#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, #stop, #stopped?, #terminate, #transient?, #traverse

Constructor Details

#initialize(parent = nil, selector: nil) ⇒ Scheduler

Returns a new instance of Scheduler.



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# File 'lib/async/scheduler.rb', line 39

def initialize(parent = nil, selector: nil)
  super(parent)
  
  @selector = selector || ::IO::Event::Selector.new(Fiber.current)
  @interrupted = false
  
  @blocked = 0
  
  @timers = ::Timers::Group.new
end

Class Method Details

.supported? ⇒ Boolean

Whether the fiber scheduler is supported.

Returns:



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# File 'lib/async/scheduler.rb', line 35

def self.supported?
  true
end

Instance Method Details

#address_resolve(hostname) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 151

def address_resolve(hostname)
  ::Resolv.getaddresses(hostname)
end

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

Deprecated.

With no replacement.

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.



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# File 'lib/async/scheduler.rb', line 259

def async(*arguments, **options, &block)
  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.logger.debug "Initial execution of task #{fiber} complete (#{result} -> #{fiber.alive?})..."
  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 110

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 



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# File 'lib/async/scheduler.rb', line 51

def close
  # This is a critical step. Because tasks could be stored as instance variables, and since the reactor is (probably) going out of scope, we need to ensure they are stopped. Otherwise, the tasks will belong to a reactor that will never run again and are not stopped.
  self.terminate
  
  Kernel::raise "Closing scheduler with blocked operations!" if @blocked > 0
  
  # We depend on GVL for consistency:
  # @guard.synchronize do
  
  @selector&.close
  @selector = nil
  
  # end
  
  consume
end

#closed? ⇒ Boolean

Returns:



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# File 'lib/async/scheduler.rb', line 70

def closed?
  @selector.nil?
end

#fiber ⇒ Object 



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# File 'lib/async/scheduler.rb', line 275

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 79

def interrupt
  @interrupted = true
  @selector.wakeup
end

#io_read(io, buffer, length) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 177

def io_read(io, buffer, length)
  @selector.io_read(Fiber.current, io, buffer, length)
end

#io_wait(io, events, timeout = nil) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 156

def io_wait(io, events, timeout = nil)
  fiber = Fiber.current
  
  if timeout
    timer = @timers.after(timeout) do
      fiber.raise(TimeoutError)
    end
  end
  
  # Console.logger.info(self, "-> io_wait", fiber, io, events)
  events = @selector.io_wait(fiber, io, events)
  # Console.logger.info(self, "<- io_wait", fiber, io, events)
  
  return events
rescue TimeoutError
  return false
ensure
  timer&.cancel
end

#io_write(io, buffer, length) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 181

def io_write(io, buffer, length)
  @selector.io_write(Fiber.current, io, buffer, length)
end

#kernel_sleep(duration = nil) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 142

def kernel_sleep(duration = nil)
  if duration
    self.block(nil, duration)
  else
    self.transfer
  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 191

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 96

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

#raise(*arguments) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 100

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

#resume(fiber, *arguments) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 104

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.



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# File 'lib/async/scheduler.rb', line 232

def run(...)
  Kernel::raise RuntimeError, 'Reactor has been closed' if @selector.nil?
  
  initial_task = self.async(...) if block_given?
  
  @interrupted = false
  
  while self.run_once
    if @interrupted
      break
    end
  end
  
  return initial_task
ensure
  Console.logger.debug(self) {"Exiting run-loop because #{$! ? $! : 'finished'}."}
end

#run_once(timeout = nil) ⇒ Object

Run one iteration of the event loop.



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# File 'lib/async/scheduler.rb', line 198

def run_once(timeout = nil)
  Kernel::raise "Running scheduler on non-blocking fiber!" unless Fiber.blocking?
  
  # If we are finished, we stop the task tree and exit:
  if self.finished?
    return false
  end
  
  interval = @timers.wait_interval
  
  # If there is no interval to wait (thus no timers), and no tasks, we could be done:
  if interval.nil?
    # Allow the user to specify a maximum interval if we would otherwise be sleeping indefinitely:
    interval = timeout
  elsif interval < 0
    # We have timers ready to fire, don't sleep in the selctor:
    interval = 0
  elsif timeout and interval > timeout
    interval = timeout
  end
  
  begin
    @selector.select(interval)
  rescue Errno::EINTR
    # Ignore.
  end
  
  @timers.fire
  
  # The reactor still has work to do:
  return true
end

#timeout_after(duration, exception, message, &block) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 295

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 74

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 85

def transfer
  @selector.transfer
end

#unblock(blocker, fiber) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 133

def unblock(blocker, fiber)
  # $stderr.puts "unblock(#{blocker}, #{fiber})"
  
  # This operation is protected by the GVL:
  @selector.push(fiber)
  @selector.wakeup
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 281

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 if timer
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 90

def yield
  @selector.yield
end