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

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 32

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:

  • (Boolean) 


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# File 'lib/async/scheduler.rb', line 28

def self.supported?
  true
end

Instance Method Details

#address_resolve(hostname) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 158

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.

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 271

def async(*arguments, **options, &block)
  Kernel::raise ClosedError if @selector.nil?
  
  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 115

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 50

def close
  # It's critical to stop all tasks. Otherwise they might be holding on to resources which are never closed/released correctly.
  until self.terminate
    self.run_once
  end
  
  Kernel.raise "Closing scheduler with blocked operations!" if @blocked > 0
  
  # We depend on GVL for consistency:
  # @guard.synchronize do
  
  # 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
  
  # end
  
  consume
end

#closed? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/async/scheduler.rb', line 74

def closed?
  @selector.nil?
end

#fiber ⇒ Object 



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# File 'lib/async/scheduler.rb', line 289

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 84

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

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



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# File 'lib/async/scheduler.rb', line 187

def io_read(io, buffer, length, offset = 0)
  @selector.io_read(Fiber.current, io, buffer, length, offset)
end

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



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# File 'lib/async/scheduler.rb', line 166

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, offset = 0) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 192

def io_write(io, buffer, length, offset = 0)
  @selector.io_write(Fiber.current, io, buffer, length, offset)
end

#kernel_sleep(duration = nil) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 149

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 203

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 101

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

#raise(*arguments) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 105

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

#resume(fiber, *arguments) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 109

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 244

def run(...)
  Kernel::raise ClosedError 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 210

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

#scheduler_close ⇒ Object 



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# File 'lib/async/scheduler.rb', line 43

def scheduler_close
  self.run
ensure
  self.close
end

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



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# File 'lib/async/scheduler.rb', line 309

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 78

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 90

def transfer
  @selector.transfer
end

#unblock(blocker, fiber) ⇒ Object 



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# File 'lib/async/scheduler.rb', line 138

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 295

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 95

def yield
  @selector.yield
end