poco经常卡死在某个方法里

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多线程执行poco一系列操作，比如poco.exists()等，在操作poco时已加上锁（以前未加锁也经常出现，现在加了锁还是会出现，只是概率少了）
已排除以下因素：
1，手机问题，用了多台手机测试，均会出现，应该与手机无关
2，系统问题，在win7.64，树莓派，ubuntu16.64系统都会出现

**描述问题bug**

```
# 以下为测试代码 ===>>>

#!/usr/bin/python3
# coding: utf-8

import logging, os, sys
sys.path.append(os.path.dirname(__file__))

from airtest.core.api import *
import random, time, threading
from airtest.core.api import *
from airtest.core.android.android import Android

from poco.drivers.android.uiautomation import AndroidUiautomationPoco

package_name = 'com.planet.light2345'
poco = None
devicex = None
logger = None

lock = threading.Lock()

def run():
global devicex, poco, logger
logger = init_logger('test')

devicex = connect_device('android:///')

logger.info(devicex)

poco = AndroidUiautomationPoco(devicex, use_airtest_input=True, screenshot_each_action=False)
auto_setup(__file__)

_run()

def init_logger(device_id):
logger = logging.getLogger(device_id)
logger.setLevel(logging.INFO)
handler = logging.StreamHandler()
formatter = logging.Formatter(
fmt='[%(asctime)s][%(levelname)s][%(filename)s:%(lineno)d] %(message)s',
datefmt='%Y-%m-%d %I:%M:%S'
)
handler.setFormatter(formatter)
logger.addHandler(handler)

return logger

def _run():
t = threading.Thread(target=_thread)
t.setDaemon(True)
t.start()

sleep(3)

_main()

def _thread():
logger.info('_thread start')
c = 0
while True:
logger.info('_thread..... %s 1 ***', c)
lock.acquire()
logger.info('_thread..... %s 2 ***', c)
poco('hehehexfee').exists()
logger.info('_thread..... %s 3 ***', c)
keyevent('BACK')
logger.info('_thread..... %s 5 ***', c)
lock.release()
logger.info('_thread..... %s 6 ***', c)

sleep(0.04)
c += 1

logger.info('_thread..... <<<<<<--------------------')

def _main():
logger.info('_main start')
c = 0
while True:
logger.info('_main....=>> 1 %s--', c)
lock.acquire()
logger.info('_main....=>> 2 %s--', c)
poco('(47209502309nbek').exists()
logger.info('_main....=>> 4 %s--', c)
poco.swipe([0.4, 0.2], [0.46, 0.58], duration=0.3)
logger.info('_main....=>> 5 %s--', c)
lock.release()
logger.info('_main....=>> 7 %s--', c)

sleep(0.08)
c += 1

logger.info('_main (((==============..........')

if __name__ in ['__main__', 'airtest.cli.runner']:
run()

```

```
# 以下为log，以及ctrl＋C后的信息
[2019-09-03 05:29:58][INFO][mmx.py:82] _main....=>> 1 354--
[2019-09-03 05:29:59][INFO][mmx.py:67] _thread..... 357 5 ***
[2019-09-03 05:29:59][INFO][mmx.py:69] _thread..... 357 6 ***
[2019-09-03 05:29:59][INFO][mmx.py:84] _main....=>> 2 354--
[2019-09-03 05:29:59][INFO][mmx.py:61] _thread..... 358 1 ***
[2019-09-03 05:29:59][INFO][mmx.py:86] _main....=>> 4 354--
[2019-09-03 05:30:00][INFO][mmx.py:88] _main....=>> 5 354--
[2019-09-03 05:30:00][INFO][mmx.py:90] _main....=>> 7 354--
[2019-09-03 05:30:00][INFO][mmx.py:63] _thread..... 358 2 ***
[2019-09-03 05:30:00][INFO][mmx.py:82] _main....=>> 1 355--

# 到这一步，程序已卡死，没有再执行下去，以下为 Ctrl＋C后的报错信息

^CTraceback (most recent call last):
File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 380, in _make_request
[pocoservice.apk] stdout: b'\ncom.netease.open.pocoservice.InstrumentedTestAsLauncher:'
[pocoservice.apk] stderr: b''
httplib_response = conn.getresponse(buffering=True)
TypeError: getresponse() got an unexpected keyword argument 'buffering'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/usr/local/lib/python3.6/dist-packages/airtest/__main__.py", line 6, in
main()
File "/usr/local/lib/python3.6/dist-packages/airtest/cli/__main__.py", line 16, in main
run_script(args)
File "/usr/local/lib/python3.6/dist-packages/airtest/cli/runner.py", line 138, in run_script
result = unittest.TextTestRunner(verbosity=0).run(suite)
File "/usr/lib/python3.6/unittest/runner.py", line 176, in run
test(result)
File "/usr/lib/python3.6/unittest/suite.py", line 84, in __call__
return self.run(*args, **kwds)
File "/usr/lib/python3.6/unittest/suite.py", line 122, in run
test(result)
File "/usr/lib/python3.6/unittest/case.py", line 653, in __call__
return self.run(*args, **kwds)
File "/usr/lib/python3.6/unittest/case.py", line 605, in run
testMethod()
File "/usr/local/lib/python3.6/dist-packages/airtest/cli/runner.py", line 61, in runTest
exec(compile(code.encode("utf-8"), pyfilepath, 'exec'), self.scope)
File "/home/yang/mmx.py", line 109, in
run()
File "/home/yang/mmx.py", line 37, in run
_run()
File "/home/yang/mmx.py", line 60, in _run
_main()
File "/home/yang/mmx.py", line 92, in _main
poco('(47209502309nbek').exists()
File "/usr/local/lib/python3.6/dist-packages/poco/proxy.py", line 72, in wrapped
return func(proxy, *args, **kwargs)
File "/usr/local/lib/python3.6/dist-packages/poco/proxy.py", line 774, in exists
return self.attr('visible')
File "/usr/local/lib/python3.6/dist-packages/poco/proxy.py", line 39, in wrapped
return func(self, *args, **kwargs)
File "/usr/local/lib/python3.6/dist-packages/poco/proxy.py", line 734, in attr
nodes = self._do_query(multiple=False)
File "/usr/local/lib/python3.6/dist-packages/poco/proxy.py", line 872, in _do_query
self._nodes = self.poco.agent.hierarchy.select(self.query, multiple)
File "/usr/local/lib/python3.6/dist-packages/poco/utils/retry.py", line 15, in wrapped
return func(*args, **kwargs)
File "/usr/local/lib/python3.6/dist-packages/poco/utils/hrpc/hierarchy.py", line 33, in select
return self.selector.select(query, multiple)
File "/usr/local/lib/python3.6/dist-packages/hrpc/object_proxy.py", line 92, in __call__
return self._client__.evaluate(self.__call_no_evaluate__(remote_obj_cache, *args))
File "/usr/local/lib/python3.6/dist-packages/hrpc/client.py", line 63, in evaluate
self.transport.send({'id': reqid, 'uri': obj_proxy._uri__, 'method': obj_proxy._invocation_path__})
File "/usr/local/lib/python3.6/dist-packages/hrpc/transport/http.py", line 23, in send
r = requests.post(self.endpoint, data=json.dumps(req), headers={'Content-Type': 'application/json'})
File "/usr/lib/python3/dist-packages/requests/api.py", line 112, in post
return request('post', url, data=data, json=json, **kwargs)
File "/usr/lib/python3/dist-packages/requests/api.py", line 58, in request
return session.request(method=method, url=url, **kwargs)
File "/usr/lib/python3/dist-packages/requests/sessions.py", line 520, in request
resp = self.send(prep, **send_kwargs)
File "/usr/lib/python3/dist-packages/requests/sessions.py", line 630, in send
r = adapter.send(request, **kwargs)
File "/usr/lib/python3/dist-packages/requests/adapters.py", line 440, in send
timeout=timeout
File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 601, in urlopen
chunked=chunked)
File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 383, in _make_request
httplib_response = conn.getresponse()
File "/usr/lib/python3.6/http/client.py", line 1331, in getresponse
response.begin()
File "/usr/lib/python3.6/http/client.py", line 297, in begin
version, status, reason = self._read_status()
File "/usr/lib/python3.6/http/client.py", line 258, in _read_status
line = str(self.fp.readline(_MAXLINE + 1), "iso-8859-1")
File "/usr/lib/python3.6/socket.py", line 586, in readinto
return self._sock.recv_into(b)
KeyboardInterrupt
[03:16:23][DEBUG] /usr/local/lib/python3.6/dist-packages/airtest/core/android/static/adb/linux/adb -s 721QACRG644X7 forward --remove tcp:14405
[03:16:23][DEBUG] /usr/local/lib/python3.6/dist-packages/airtest/core/android/static/adb/linux/adb -s 721QACRG644X7 forward --remove tcp:18106
[03:16:23][DEBUG] /usr/local/lib/python3.6/dist-packages/airtest/core/android/static/adb/linux/adb -s 721QACRG644X7 forward --remove tcp:13054

```

**执行脚本命令:** `python3 -m airtest run mmx.py`
**python 版本:** `Python 3.6.7`

**airtest 版本:** `airtest==1.0.27`
> airtest版本通过`pip freeze`可以命令可以查到

**其他相关环境信息**
在win7.64，树莓派，ubuntu16.64系统都会出现卡死现象