class Async::Pool::Controller

def initialize(constructor, limit: nil, concurrency: (limit || 1), policy: nil, tags: nil)

@parameter policy [Policy] The pool policy.
@parameter concurrency [Integer] The maximum number of concurrent tasks that can be creating a new resource.
@parameter limit [Integer | Nil] The maximum number of resources that this pool can have at any given time. If nil, the pool can have an unlimited number of resources.
@parameter constructor [Proc] A block which creates a new resource.

Create a new resource pool. 
def initialize(constructor, limit: nil, concurrency: (limit || 1), policy: nil, tags: nil)
	@constructor = constructor
	@limit = limit
	
	# This semaphore is used to limit the number of concurrent tasks which are creating new resources.
	@guard = Async::Semaphore.new(concurrency)
	
	@policy = policy
	@gardener = nil
	
	@tags = tags
	
	# All available resources:
	@resources = {}
	
	# Resources which may be available to be acquired:
	# This list may contain false positives, or resources which were okay but have since entered a state which is unusuable.
	@available = []
	
	# Used to signal when a resource has been released:
	@notification = Async::Notification.new
end