class Tins::Limited

def initialize(maximum, name: nil)

Create a Limited instance, that runs _maximum_ threads at most. 
def initialize(maximum, name: nil)
  @maximum  = Integer(maximum)
  raise ArgumentError, "maximum < 1" if @maximum < 1
  @mutex    = Mutex.new
  @continue = ConditionVariable.new
  @name     = name
  @count    = 0
  @tg       = ThreadGroup.new
end