threading.local在flask中的用法

一、介绍

threading.local的作用：

多个线程修改同一个数据，复制多份变量给每个线程用，为每个线程开辟一块空间进行数据的存储，而每块空间内的数据也不会错乱。

二、不使用threading.local会导致数据错乱

# 不用local
from threading import Thread
import time
lqz = -1
def task(arg):
    global lqz
    lqz = arg
    # time.sleep(2)
    print(lqz)

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

三、使用threading.local

from threading import Thread
from threading import local
import time
from threading import get_ident
# 特殊的对象
lqz = local()
def task(arg):
    # 对象.val = 1/2/3/4/5
    lqz.value = arg
    time.sleep(2)
    print(lqz.value)
for i in range(10):
    t = Thread(target=task,args=(i,))
    t.start()

四、通过字典自定义threading.local（函数）

from threading import get_ident,Thread
import time
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)
    v = get('val')
    print(v)

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

五、每个对象有自己的存储空间（字典）

from threading import get_ident,Thread
import time
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
    obj.xxx = arg
    print(obj.val)
for i in range(10):
    t = Thread(target=task,args=(i,))
    t.start()

六、兼容线程和协程

try:
    from greenlet import getcurrent as get_ident
except Exception as e:
    from threading import get_ident
from threading import Thread
import time
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
    obj.xxx = arg
    print(obj.val)
for i in range(10):
    t = Thread(target=task,args=(i,))
    t.start()