text: # MIT License
  #
  # Copyright (c) 2018 Evgeny Medvedev, evge.medvedev@gmail.com
  #
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be included in all
  # copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  # SOFTWARE.
  
  
  from concurrent.futures import ThreadPoolExecutor
  from threading import BoundedSemaphore
  
  
  class BoundedExecutor:
      """BoundedExecutor behaves as a ThreadPoolExecutor which will block on
      calls to submit() once the limit given as "bound" work items are queued for
      execution.
      :param bound: Integer - the maximum number of items in the work queue
      :param max_workers: Integer - the size of the thread pool
      """
  
      def __init__(self, bound, max_workers):
          self._delegate = ThreadPoolExecutor(max_workers=max_workers)
          self._semaphore = BoundedSemaphore(bound + max_workers)
  
      def submit(self, fn, *args, **kwargs):
          """See concurrent.futures.Executor#submit"""
          self._semaphore.acquire()
          try:
              future = self._delegate.submit(fn, *args, **kwargs)
          except:
              self._semaphore.release()
              raise
          else:
              future.add_done_callback(lambda x: self._semaphore.release())
              return future
  
      def shutdown(self, wait=True):
          """See concurrent.futures.Executor#shutdown"""
          self._delegate.shutdown(wait)
  