线程安全的单例不起作用。 Python答案

【问题标题】：Thread-safe Singleton doesn't work. Python线程安全的单例不起作用。 Python
【发布时间】：2015-10-07 18:03:37
【问题描述】：

我试图找到这个post 中描述的错误，然后我找到了。

这是 Singleton 类，我从 StackOverflow 中通过 post 提供的

当我开始测试该类时，我发现该程序崩溃了（就像第一个链接中描述的那样）...

这是导致错误的最小示例：

Singleton.py

import threading


class Singleton(object):
    __singleton_lock = threading.Lock()
    __singleton_instance = None

    @classmethod
    def Instance(cls):
        if not cls.__singleton_instance:
            with cls.__singleton_lock:
                if not cls.__singleton_instance:
                    cls.__singleton_instance = cls()
        return cls.__singleton_instance

Data.py

#-*- coding: utf-8 -*-
from singletone import Singleton
import threading


class Data(Singleton):

    def __init__(self):
        self.task_table = {"Zadanie1.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie2.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie3.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie4.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie5.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie6.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie7.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie8.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie9.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie10.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie11.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie12.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie13.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie14.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie15.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie16.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie17.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie18.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie19.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie20.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie21.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie22.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie23.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie24.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie25.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie26.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie27.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie28.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie29.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie30.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie31.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie32.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie33.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie34.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie35.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie36.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie37.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie38.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie39.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie40.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie41.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie42.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie43.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie44.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie45.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie46.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie47.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie48.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie49.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie50.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie51.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie52.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie53.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie54.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie55.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie56.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie57.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie58.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie59.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie60.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie61.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie62.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie63.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie64.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie65.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie66.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie67.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie68.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie69.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie70.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie71.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie72.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie73.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie74.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie75.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie76.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie77.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie78.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie79.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie80.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie81.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie82.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie83.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie84.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie85.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie86.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie87.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie88.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie89.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie90.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie91.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie92.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie93.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie94.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie95.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie96.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie97.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie98.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie99.py": {'status': 'uncomplete', 'result': '', 'time': 0}, "Zadanie100.py": {'status': 'uncomplete', 'result': '', 'time': 0}}
        self.complete_task = threading.Event()
        self.complete_task.set()

    def getTotalCompleteTasks(self):
        result = 0
        for taskname in self.task_table.keys():
            if self.task_table[taskname]['status'] == 'complete':
                result += 1
        return result

Worker.py

#-*- coding: utf-8 -*-
import threading
import subprocess


class Worker(threading.Thread):

    def __init__(self, data, taskname):
        self.taskname = taskname
        self.data = data
        threading.Thread.__init__(self)

    def run(self):
        self.data.complete_task.clear()
        print u"Start executing %s" % self.taskname
        startupinfo = subprocess.STARTUPINFO()
        startupinfo.dwFlags |= subprocess.STARTF_USESHOWWINDOW
        startupinfo.wShowWindow = subprocess.SW_HIDE
        p = subprocess.Popen("C:\Python27\python.exe tasks100.5\\" + self.taskname, startupinfo=startupinfo, shell=False, stdout=subprocess.PIPE)
        job_result, err = p.communicate()
        print u"Stop executing %s" % self.taskname
        self.data.task_table[self.taskname]['status'] = 'complete'
        self.data.complete_task.set()

Agent.py

#-*- coding: utf-8 -*-
import communication_servers as cs
from worker import Worker
from data import Data
import time


app_data = Data.Instance()
SRV = cs.Server(app_data)
SRV.setDaemon(True)
SRV.start()

my_tasks = app_data.task_table.keys()[:]


while True:
    print u"Complete tasks: %d\n" % app_data.getTotalCompleteTasks()
    time.sleep(1)

    if my_tasks:
        if app_data.complete_task.is_set():
            job = Worker(app_data, my_tasks.pop())
            job.setDaemon(True)
            print u"Running"
            job.start()
        else:
            print u"Can't run"
        print u"Test string"

Communication_server.py

#-*- coding: utf-8 -*-
import threading
import time


class Server(threading.Thread):

    def __init__(self, data):
        threading.Thread.__init__(self)

    def run(self):
        while True:
            print('Server still working...\n')
            time.sleep(5)

ZadanieXX.py 之类的所有文件都在那里：

import time
i = 2
p = i**400
time.sleep(5)
print p

只有真正的代码的缩减版本。在 30 次启动的 1 例中，它会导致错误。该错误是当主 while 循环 im Agent.py 没有迭代或迭代，但 complete_task 事件从未设置（在少于 1 次的 100 次启动的情况下）。

附言我尝试使用this Singleton 模式，但 bug 仍然在这里...

任何想法，为什么它会以这种方式工作？任何建议，我如何创建单实例的线程安全类来存储所有应用程序工作数据？

我的英语不是很好。对不起。

【问题讨论】：

标签： python multithreading thread-safety singleton

【解决方案1】：

请注意，您对锁定的使用实际上不是线程安全的。检查实例是否存在和锁定对实例的访问之间存在竞争条件：

def Instance(cls):
    if not cls.__singleton_instance:
        # another thread may succeed with the previous check again here
        with cls.__singleton_lock:
            if not cls.__singleton_instance:
                cls.__singleton_instance = cls()
    return cls.__singleton_instance

你应该交换获取锁和检查__singleton_instance，因为前者保护后者。

请注意，在您的最小工作示例中，您正在显式构造单例，因此永远不会触发竞争条件（没有多线程实例化）。事实上，您的示例允许您在没有单例的情况下工作，因为您明确只实例化您的类一次。

【讨论】：

当我开始搜索错误时，我会逐步减少我的代码。我从其他线程中删除了对数据的访问。但问题仍然存在。在所有这项工作之前，一个没有Lock() 的单例，它工作正常，除了一个错误。之后，我将这个 Singleton 与线程安全一起使用（如链接 2 中的作者所述）。和错误仍然在这里。我不明白：单例是一个问题，还是其他问题。
你运行这个例子得到了错误吗？
@gek0n 我无法运行您的示例，因为它具有特定于 Windows 的代码，例如 subprocess.STARTUPINFO。同样，您的单例实现存在错误，但这不是您的问题，因为您的程序不依赖它。
@gek0n 修复 windows 依赖后，我仍然无法运行您的代码，因为它正在调用不存在的代码/脚本（tasks100.5 文件）。
对不起。我在我的问题中添加了“Zadanie”模板的示例。就像time.sleep(5)

【解决方案2】：

很抱歉这不是关于 Singleton DP 的答案，但我认为没有理由必须使用 Singleton。

在您的示例中，Data 类仅用作数据存储，您可以使用 python 自己的模块Queue 进行单个数据存储。

8.10. Queue - A synchronized queue class

Queue 模块实现了多生产者、多消费者队列。当必须在多个线程之间安全地交换信息时，它在线程编程中特别有用。该模块中的 Queue 类实现了所有必需的锁定语义。这取决于 Python 中线程支持的可用性；查看线程模块。

是的。它是线程安全的，因此您可以将 Queue 作为您的单一中心数据存储。

检查类似的东西。

#-*- coding: utf-8 -*-
from Queue import Queue
from threading import Thread
import time

# Set up some global variables
num_threads = 2
data_queue = Queue()

# Your Data
files = ['Zadanie1.py', 'Zadanie2.py', ... ]

def doSomething(i, q):
    while True:
        print '[{}] Waiting...'.format(i)
        filename = q.get()
        print '[{}] Working: {} '.format(i, filename)
        # Do something you need
        time.sleep(i + random.randint(1, 5))
        q.task_done()

# Set up threads
for i in range(num_threads):
    worker = Thread(target=doSomething, args=(i, data_queue,))
    worker.setDaemon(True)
    worker.start()
    # Note that you can start threads before filling queue,
    # because queue.get() will block until queue has data to return.

# Fill queue
for filename in files:
    print 'Queuing: {}'.format(filename)
    data_queue.put(filename)

# Wait for the queue to be empty.
data_queue.join()
print 'Done!'

结果会是这样的。

[0] Waiting...
[1] Waiting...
Queuing: Zadanie1.py
Queuing: Zadanie2.py
...
[1] Working: Zadanie1.py 
[0] Working: Zadanie2.py 
...
[0] Waiting...
[1] Waiting...
Done!

希望这有帮助！

【讨论】：

没有任何其他“正确”的答案，你的建议很有帮助，所以我认为 50 声望是你的。