code: def _process_queue(self):
      with stack_context.NullContext():
          while True:
              started = 0
              while self._free_list and self._requests:
                  started += 1
                  curl = self._free_list.pop()
                  (request, callback) = self._requests.popleft()
                  curl.info = {
                      "headers": httputil.HTTPHeaders(),
                      "buffer": BytesIO(),
                      "request": request,
                      "callback": callback,
                      "curl_start_time": time.time(),
                  }
                  try:
                      self._curl_setup_request(
                          curl,
                          request,
                          curl.info["buffer"],
                          curl.info["headers"],
                      )
                  except Exception as e:
                      # If there was an error in setup, pass it on
                      # to the callback. Note that allowing the
                      # error to escape here will appear to work
                      # most of the time since we are still in the
                      # caller's original stack frame, but when
                      # _process_queue() is called from
                      # _finish_pending_requests the exceptions have
                      # nowhere to go.
                      self._free_list.append(curl)
                      callback(
                          HTTPResponse(
                              request=request, code=599, error=e
                          )
                      )
                  else:
                      self._multi.add_handle(curl)
  
              if not started:
                  break
  
imports: from __future__ import absolute_import, division, print_function
  import collections
  import functools
  import logging
  import pycurl
  import threading
  import time
  from io import BytesIO
  from tornado import httputil
  from tornado import ioloop
  from tornado import stack_context
  from tornado.escape import utf8, native_str
  from tornado.httpclient import HTTPResponse, HTTPError, AsyncHTTPClient, main
label_desc: Use image node_id 10 for calling the CurlAsyncHTTPClient obj's underlying member method code with example usage: obj._process_queue() without return types