multiprocessing.Pool-PicklingError：无法腌制 ：属性查找thread.lock失败

Question

multiprocessing.Pool令我发疯……
我想升级许多软件包，对于每个软件包，我都必须检查是否有更大的版本。这是通过check_one函数来完成的。
主要代码在Updater.update方法中：在此处创建Pool对象并调用该map()方法。

这是代码：

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

多重处理通过传递任务（包括check_one和data）到工作进程mp.SimpleQueue。与Queue.Queues不同，放入s中的所有内容都mp.SimpleQueue必须是可挑选的。Queue.Queues不可选：

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datainclude包括packages一个Queue.Queue。这可能是问题的根源。

---

这是一个可能的解决方法：该方法Queue有两个用途：

1. 找出大概的大小（通过调用qsize）
2. 存储结果供以后检索。

qsize我们可以使用而不是在多个进程之间共享值，而无需调用mp.Value。

除了将结果存储在队列中之外，我们可以（并且应该）仅从调用返回值check_one。该pool.map在自己制作的队列中收集结果，并返回结果的返回值pool.map。

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()