flask框架（十二）：上下文管理***

情况一：单进程单线程

　　基于全局变量实现。

情况二：单进程多线程

　　基于threading.local对象。

　　threading.local对象，用于为每个线程开辟一块空间来保存它独有的值。

# -*- coding: utf-8 -*-

# @Author : Felix Wang

# @time   : 2018/7/5 15:43

import threading

# 使用threading.local()时取到的是想要的值，数据操作是安全的

local_values = threading.local()

# 没有使用threading.local()时，取到的不是自己想要的值

# class Foo(object):

#     def __init__(self):

#         self.name=0

# local_values=Foo()

def func(num):

    local_values.name = num

    import time

    time.sleep(1)

    print(local_values.name, threading.current_thread().name)

for i in range(20):

    th = threading.Thread(target=func, args=(i,), name='线程{}'.format(str(i)))

    th.start()

单进程多线程情况

情况三：单进程单线程（多个协程），threading.local对象做不到。通过自定义类似threading.local对象

# -*- coding: utf-8 -*-

# @Author : Felix Wang

# @time   : 2018/7/5 16:06

import threading

try:

    from greenlet import getcurrent as get_ident  # 支持协程

except ImportError:

    try:

        from thread import get_ident

    except ImportError:

        from _thread import get_ident  # 获取线程的唯一标识

# 实现方式一

class Local(object):

    def __init__(self):

        self.storage = {}

        self.get_ident = get_ident

    def set(self, k, v):

        ident = self.get_ident()

        origin = self.storage.get(ident)

        if not origin:

            origin = {k: v}

        else:

            origin[k] = v

        self.storage[ident] = origin

    def get(self, k):

        ident = self.get_ident()

        origin = self.storage.get(ident)

        if not origin:

            return None

        return origin.get(k, None)

local_values = Local()

def task(num):

    local_values.set('name', num)

    import time

    time.sleep(1)

    print(local_values.get('name'), threading.current_thread().name)

for i in range(20):

    th = threading.Thread(target=task, args=(i,))

    th.start()

# 实现方式二

class Local2(object):

    def __init__(self):

        object.__setattr__(self, '__storage__', {})

        object.__setattr__(self, '__ident_func__', get_ident)

        # self.storage = {}

        # self.get_ident = get_ident

    def __getattr__(self, name):

        try:

            return self.__storage__[self.__ident_func__()][name]

        except KeyError:

            raise AttributeError(name)

    def __setattr__(self, key, value):

        ident = self.__ident_func__()

        storage = self.__storage__

        try:

            storage[ident][key] = value

        except KeyError:

            storage[ident] = {key: value}

local_values2 = Local2()

def task(num):

    local_values2.name = num

    import time

    time.sleep(1)

    print(local_values2.name, threading.current_thread().name)

for i in range(20, 40):

    th = threading.Thread(target=task, args=(i,))

    th.start()

自定义local对象