单例模式四种方式
单例模式：单例模式就是一个单个实例公用一个对象
1.文件导入（比较常用）
2.基于类
无法支持多线程
import threading
class Singleton(object):
def __init__(self):
pass
@classmethod
def instance(cls, *args, **kwargs):
if not hasattr(Singleton, "_instance"):
Singleton._instance = Singleton(*args, **kwargs)
return Singleton._instance
obj = Singleton.instance()
View Code支持多线程
import time
import threading
class Singleton(object):
_instance_lock = threading.Lock()
def __init__(self):
time.sleep(1)
@classmethod
def instance(cls, *args, **kwargs):
if not hasattr(Singleton, "_instance"):
with Singleton._instance_lock:
if not hasattr(Singleton, "_instance"):
Singleton._instance = Singleton(*args, **kwargs)
return Singleton._instance
# 第一次调用
def task(arg):
obj = Singleton.instance()
print(obj)
for i in range(10):
t = threading.Thread(target=task,args=[i,])
t.start()
# 第二次调用
time.sleep(20)
obj = Singleton.instance()
View Code
3.使用__new__（最常用）
无法支持多线程
class Singleton(object):
Singleton._instance = None
def __init__(self):
pass
def __new__(cls, *args, **kwargs):
if not hasattr(Singleton, "_instance"):
Singleton._instance = object.__new__(cls, *args, **kwargs)
return Singleton._instance
View Code
支持多线程
class Singleton(object):
_instance_lock = threading.Lock()
def __init__(self):
pass
def __new__(cls, *args, **kwargs):
if not hasattr(Singleton, "_instance"):
with Singleton._instance_lock:
if not hasattr(Singleton, "_instance"):
Singleton._instance = object.__new__(cls, *args, **kwargs)
return Singleton._instance
View Code
4.基于metaclass
-------------------------------(一)-------------------------------
# 创建对象
class SingletonType(type):
def __call__(cls, *args, **kwargs):
obj = super(SingletonType,cls).__call__(*args, **kwargs) #type类帮创建__new__和__init__并返回
return obj
class Foo(metaclass=SingletonType):
def __init__(self,name):
self.name = name
obj = Foo("alex")
-------------------------------(二)-------------------------------
import threading
class SingletonType(type):
_instance_lock = threading.Lock()
def __call__(cls, *args, **kwargs):
if not hasattr(cls, "_instance"):
with SingletonType._instance_lock:
if not hasattr(cls, "_instance"):
cls._instance = super(SingletonType,cls).__call__(*args, **kwargs)
return cls._instance
class Foo(metaclass=SingletonType):
def __init__(self,name):
self.name = name
obj1 = Foo(‘name‘)
obj2 = Foo(‘name‘)
print(obj1,obj2)
