Class: Async::Semaphore

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

Overview

A synchronization primitive, which limits access to a given resource.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(limit = 1, parent: nil) ⇒ Semaphore

Returns a new instance of Semaphore.



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# File 'lib/async/semaphore.rb', line 14

def initialize(limit = 1, parent: nil)
	@count = 0
	@limit = limit
	@waiting = List.new
	
	@parent = parent
end

Instance Attribute Details

#count ⇒ Object (readonly)

The current number of tasks that have acquired the semaphore.



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# File 'lib/async/semaphore.rb', line 23

def count
  @count
end

#limit ⇒ Object

The maximum number of tasks that can acquire the semaphore.



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# File 'lib/async/semaphore.rb', line 26

def limit
  @limit
end

#waiting ⇒ Object (readonly)

The tasks waiting on this semaphore.



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# File 'lib/async/semaphore.rb', line 29

def waiting
  @waiting
end

Instance Method Details

#acquire ⇒ Object

Acquire the semaphore, block if we are at the limit. If no block is provided, you must call release manually.



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# File 'lib/async/semaphore.rb', line 79

def acquire
	wait
	
	@count += 1
	
	return unless block_given?
	
	begin
		return yield
	ensure
		self.release
	end
end

#async(*arguments, parent: (@parent or Task.current), **options) ⇒ Object

Run an async task. Will wait until the semaphore is ready until spawning and running the task.



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# File 'lib/async/semaphore.rb', line 61

def async(*arguments, parent: (@parent or Task.current), **options)
	wait
	
	parent.async(**options) do |task|
		@count += 1
		
		begin
			yield task, *arguments
		ensure
			self.release
		end
	end
end

#blocking? ⇒ Boolean

Whether trying to acquire this semaphore would block.

Returns:

  • (Boolean) 


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# File 'lib/async/semaphore.rb', line 56

def blocking?
	@count >= @limit
end

#empty? ⇒ Boolean

Is the semaphore currently acquired?

Returns:

  • (Boolean) 


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

def empty?
	@count.zero?
end

#release ⇒ Object

Release the semaphore. Must match up with a corresponding call to ‘acquire`. Will release waiting fibers in FIFO order.



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# File 'lib/async/semaphore.rb', line 94

def release
	@count -= 1
	
	while (@limit - @count) > 0 and node = @waiting.first
		node.resume
	end
end