threading.local作用及原理

先看下应用：

import threading
from threading import local
import time

obj = local()


def task(i):
    obj.xxxxx = i
    time.sleep(2)
    print(obj.xxxxx,i)

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

上述代码实现了线程间的隔离，为每个线程开辟了独立的空间，这就是threading.local的作用

再看下面代码

import time
import threading


DIC = {}

def task(i):

    ident = threading.get_ident()
    if ident in DIC:
        DIC[ident]['xxxxx'] = i
    else:
        DIC[ident] = {'xxxxx':i }
    time.sleep(2)

    print(DIC[ident]['xxxxx'],i)

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

上述代码使用字典实现了和threading.local一样的功能，其实就是threading.local实现的原理。

再看下面代码：

import time
import threading
import greenlet

DIC = {}

def task(i):

    # ident = threading.get_ident()
    ident = greenlet.getcurrent()
    if ident in DIC:
        DIC[ident]['xxxxx'] = i
    else:
        DIC[ident] = {'xxxxx':i }
    time.sleep(2)

    print(DIC[ident]['xxxxx'],i)

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

上面代码就是threading.local功能的加强版：支持协程！

接着看：

import time
import threading
try:
    import greenlet
    get_ident =  greenlet.getcurrent
except Exception as e:
    get_ident = threading.get_ident

class Local(object):
    DIC = {}

    def __getattr__(self, item):
        ident = get_ident()
        if ident in self.DIC:
            return self.DIC[ident].get(item)
        return None

    def __setattr__(self, key, value):
        ident = get_ident()
        if ident in self.DIC:
            self.DIC[ident][key] = value
        else:
            self.DIC[ident] = {key:value}


obj = Local()

def task(i):
    obj.xxxxx = i
    time.sleep(2)
    print(obj.xxxxx,i)

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

上述代码自己实现了threading.local的数据隔离，并支持协程。