text: # Copyright 2019 Novartis Institutes for BioMedical Research Inc. Licensed
  # under the Apache License, Version 2.0 (the "License"); you may not use
  # this file except in compliance with the License. You may obtain a copy
  # of the License at http://www.apache.org/licenses/LICENSE-2.0. Unless
  # required by applicable law or agreed to in writing, software distributed
  # under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES
  # OR CONDITIONS OF ANY KIND, either express or implied. See the License for
  # the specific language governing permissions and limitations under the License.
  
  import time
  import logging
  
  from cellxgene_gateway.util import current_time_stamp
  from cellxgene_gateway.env import ttl
  
  
  class PruneProcessCache:
      def __init__(self, cache):
          self.cache = cache
          self.expire_seconds = (3600 if ttl is None else int(ttl))
  
      def __call__(self):
          while True:
              time.sleep(60)
              self.prune()
  
      def prune(self):
          timestamp = current_time_stamp()
          cutoff = timestamp - self.expire_seconds
          processes_to_delete = [p for p in self.cache.entry_list if  p.timestamp < cutoff]
          processes_to_keep = [p for p in self.cache.entry_list if not p.timestamp < cutoff]
          logger = logging.getLogger("cellxgene_gateway")
          logger.debug(f"Cutoff {cutoff} = timestamp {timestamp} - expire seconds {self.expire_seconds} , keeping {processes_to_keep}")
          
          for process in processes_to_delete:
              try:
                  logger.info(f"pruning process {process.pid} ({process.key.dataset})")
                  self.cache.prune(process)
              except Exception:
                  logger.exception("failed to prune process {process.pid} ({process.dataset})")
  