Flask - threading.local

示例

import time
from threading import local, Thread

num = 0


def task(arg):
    global num
    num = arg
    time.sleep(2)
    print(num)


for i in range(10):
    t = Thread(target=task, args=(i,))
    t.start()

• 使用线程每次给变量 + 1.
• 这样会使值相同, 都是最后一次改变的值.

使用threading.local避免这样的情况

import time
from threading import local, Thread

# 实例化一个local对象
num = local()


def task(arg):
    num = arg
    time.sleep(2)
    print(num)


for i in range(10):
    t = Thread(target=task, args=(i,))
    t.start()

• 这样相当于每个线程过来的时候给它开辟一个空间. 存取它们的值.

自定义Local

基于函数

import time
from threading import get_ident, Thread

storage = {}


def set(k, v):
    ident = get_ident()
    if ident in storage:
        storage[ident][k] = v
    else:
        storage[ident] = {k: v}


def get(k):
    ident = get_ident()
    return storage[ident][k]


def task(arg):
    set('val', arg)
    time.sleep(2)
    v = get('val')
    print(v)


for i in range(10):
    t = Thread(target=task, args=(i,))
    t.start()

基于面向对象

import time
from threading import get_ident, Thread


class Local(object):
    def __init__(self):
        object.__setattr__(self, 'storage', {})

    def __setattr__(self, k, v):
        ident = get_ident()
        if ident in self.storage:
            self.storage[ident][k] = v
        else:
            self.storage[ident] = {k: v}

    def __getattr__(self, k):
        ident = get_ident()
        return self.storage[ident][k]


obj = Local()


def task(arg):
    obj.val = arg
    print(obj.val)


for i in range(10):
    t = Thread(target=task, args=(i,))
    t.start()