concurrent-ruby CountDownLatch

可让一些线程等到另一些线程完成后才运行

有java和ruby两种实现

CountDownLatchImplementation = case
                               when Concurrent.on_jruby?
                                 JavaCountDownLatch
                               else
                                 MutexCountDownLatch
                               end

ruby的实现其实依赖于ConditionVariable

module Concurrent
  class MutexCountDownLatch < Synchronization::LockableObject
    def initialize(count = 1)
      Utility::NativeInteger.ensure_integer_and_bounds count
      Utility::NativeInteger.ensure_positive count

      super()
      synchronize { ns_initialize count }
    end

    def wait(timeout = nil)
      synchronize { ns_wait_until(timeout) { @count == 0 } }
    end

    def count_down
      synchronize do
        @count -= 1 if @count > 0
        ns_broadcast if @count == 0
      end
    end

    # ..

    protected

    def ns_initialize(count)
      @count = count
    end
  end
end