Question

multiprocessing.Pool让我发疯... 我想要升级许多软件包，对于每一个软件包，我都要检查是否有更大的版本。这是由check_one函数完成的主要代码在Updater.update方法中：我创建了Pool对象并调用map()方法。

以下是代码：

def check_one(args):
    res, total, package, version = args
    i = res.qsize()
    logger.info('\r[{0:.1%} - {1}, {2} / {3}]',
        i / float(total), package, i, total, addn=False)
    try:
        json = PyPIJson(package).retrieve()
        new_version = Version(json['info']['version'])
    except Exception as e:
        logger.error('Error: Failed to fetch data for {0} ({1})', package, e)
        return
    if new_version > version:
        res.put_nowait((package, version, new_version, json))

class Updater(FileManager):

    # __init__ and other methods...

    def update(self):    
        logger.info('Searching for updates')
        packages = Queue.Queue()
        data = ((packages, self.set_len, dist.project_name, Version(dist.version)) \
            for dist in self.working_set)
        pool = multiprocessing.Pool()
        pool.map(check_one, data)
        pool.close()
        pool.join()
        while True:
            try:
                package, version, new_version, json = packages.get_nowait()
            except Queue.Empty:
                break
            txt = 'A new release is avaiable for {0}: {1!s} (old {2}), update'.format(package,
                                                                                      new_version,
                                                                                      version)
            u = logger.ask(txt, bool=('upgrade version', 'keep working version'), dont_ask=self.yes)
            if u:
                self.upgrade(package, json, new_version)
            else:
                logger.info('{0} has not been upgraded', package)
        self._clean()
        logger.success('Updating finished successfully')

当我运行它时，我得到了这个奇怪的错误：

Searching for updates
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 552, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 505, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/local/lib/python2.7/dist-packages/multiprocessing/pool.py", line 225, in _handle_tasks
    put(task)
PicklingError: Can't pickle <type 'thread.lock'>: attribute lookup thread.lock failed

Answer 1

多处理通过check_one将任务（包括data和Queue.Queue）传递给工作进程。放入Queue.Queue的所有内容都必须是可选的。 Queue本身不可摘：

import multiprocessing as mp
import Queue

def foo(queue):
    pass

pool=mp.Pool()
q=Queue.Queue()

pool.map(foo,(q,))

产生此异常：

UnpickleableError: Cannot pickle <type 'thread.lock'> objects

您的data包含packages，这是一个Queue.Queue。这可能是问题的根源。

以下是可能的解决方法：Queue用于两个目的：

找出大致尺寸（通过调用qsize）
存储结果以供日后检索。

我们可以使用qsize而不是调用mp.Value来共享多个进程之间的值。

我们可以（而且应该）从调用check_one返回值，而不是将结果存储在队列中。 pool.map将结果收集到自己创建的队列中，并将结果作为pool.map的返回值返回。

例如：

import multiprocessing as mp
import Queue
import random
import logging

# logger=mp.log_to_stderr(logging.DEBUG)
logger = logging.getLogger(__name__)


qsize = mp.Value('i', 1)
def check_one(args):
    total, package, version = args
    i = qsize.value
    logger.info('\r[{0:.1%} - {1}, {2} / {3}]'.format(
        i / float(total), package, i, total))
    new_version = random.randrange(0,100)
    qsize.value += 1
    if new_version > version:
        return (package, version, new_version, None)
    else:
        return None

def update():    
    logger.info('Searching for updates')
    set_len=10
    data = ( (set_len, 'project-{0}'.format(i), random.randrange(0,100))
             for i in range(set_len) )
    pool = mp.Pool()
    results = pool.map(check_one, data)
    pool.close()
    pool.join()
    for result in results:
        if result is None: continue
        package, version, new_version, json = result
        txt = 'A new release is avaiable for {0}: {1!s} (old {2}), update'.format(
            package, new_version, version)
        logger.info(txt)
    logger.info('Updating finished successfully')

if __name__=='__main__':
    logging.basicConfig(level=logging.DEBUG)
    update()

Answer 2

经过大量挖掘类似问题......

事实证明，碰巧包含threading.Condition（）对象的任何对象永远不会使用multiprocessing.Pool。

这是一个例子

import multiprocessing as mp
import threading

class MyClass(object):
   def __init__(self):
      self.cond = threading.Condition()

def foo(mc):
   pass

pool=mp.Pool()
mc=MyClass()
pool.map(foo,(mc,))

我用Python 2.7.5运行它并遇到同样的错误：

Exception in thread Thread-2:
Traceback (most recent call last):
  File "/usr/lib64/python2.7/threading.py", line 811, in __bootstrap_inner
self.run()
  File "/usr/lib64/python2.7/threading.py", line 764, in run
self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib64/python2.7/multiprocessing/pool.py", line 342, in _handle_tasks
put(task)
PicklingError: Can't pickle <type 'thread.lock'>: attribute lookup thread.lock failed

然后在python 3.4.1上运行它，这个问题已得到解决。

虽然我还没有找到任何有用的解决方法，对于我们这些仍然在2.7.x的人。

Answer 3

我在docker上遇到python 3.6版本的问题。将版本更改为3.7.3，此问题已解决。

multiprocessing.Pool - PicklingError：无法pickle <type'strread.lock'=“”>：属性查找thread.lock失败</type>

3 个答案: