单利模式的四种方式

单利

s1.py

class Foo(object):
    def test(self):
        print("123")

v = Foo()
#v是Foo的实例

s2.py
from s1 import v as v1
print(v1,id(v1))  #<s1.Foo object at 0x0000000002221710> 35788560

from s1 import v as v2
print(v1,id(v2))   #<s1.Foo object at 0x0000000002221710> 35788560

# 两个的内存地址是一样的
# 文件加载的时候，第一次导入后，再次导入时不会再重新加载。

# ======================单例模式：无法支持多线程情况===============

class Singleton(object):

    def __init__(self):
        import time
        time.sleep(1)

    @classmethod
    def instance(cls, *args, **kwargs):
        if not hasattr(Singleton, "_instance"):
            Singleton._instance = Singleton(*args, **kwargs)
        return Singleton._instance

import threading

def task(arg):
    obj = Singleton.instance()
    print(obj)

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


# ====================单例模式：支持多线程情况================、

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:   #为了保证线程安全在内部加锁
                if not hasattr(Singleton, "_instance"):
                    Singleton._instance = Singleton(*args, **kwargs)
        return Singleton._instance


def task(arg):
    obj = Singleton.instance()
    print(obj)
for i in range(10):
    t = threading.Thread(target=task,args=[i,])
    t.start()
time.sleep(20)
obj = Singleton.instance()
print(obj)

# 使用先说明，以后用单例模式，obj = Singleton.instance()
# 示例：
# obj1 = Singleton.instance()
# obj2 = Singleton.instance()
# print(obj1,obj2)
# 错误示例
# obj1 = Singleton()
# obj2 = Singleton()
# print(obj1,obj2)

# =============单线程下执行===============
import threading
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"):
                    # 类加括号就回去执行__new__方法，__new__方法会创建一个类实例：Singleton()
                    Singleton._instance = object.__new__(cls)  # 继承object类的__new__方法，类去调用方法，说明是函数，要手动传cls
        return Singleton._instance  #obj1
        #类加括号就会先去执行__new__方法，在执行__init__方法
# obj1 = Singleton()
# obj2 = Singleton()
# print(obj1,obj2)

# ===========多线程执行单利============
def task(arg):
    obj = Singleton()
    print(obj)

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

# 使用先说明，以后用单例模式，obj = Singleton()
# 示例
# obj1 = Singleton()
# obj2 = Singleton()
# print(obj1,obj2)

"""
1.对象是类创建，创建对象时候类的__init__方法自动执行，对象()执行类的 __call__ 方法
2.类是type创建，创建类时候type的__init__方法自动执行，类() 执行type的 __call__方法(类的__new__方法,类的__init__方法)

# 第0步: 执行type的 __init__ 方法【类是type的对象】
class Foo:
    def __init__(self):
        pass

    def __call__(self, *args, **kwargs):
        pass

# 第1步: 执行type的 __call__ 方法
#        1.1  调用 Foo类（是type的对象）的 __new__方法，用于创建对象。
#        1.2  调用 Foo类（是type的对象）的 __init__方法，用于对对象初始化。
obj = Foo()
# 第2步：执行Foo的 __call__ 方法
obj()
"""

# ===========类的执行流程================
class SingletonType(type):
    def __init__(self,*args,**kwargs):
        print(self)  #会不会打印？  #<class '__main__.Foo'>
        super(SingletonType,self).__init__(*args,**kwargs)

    def __call__(cls, *args, **kwargs):  #cls = Foo
        obj = cls.__new__(cls, *args, **kwargs)
        obj.__init__(*args, **kwargs)
        return obj


class Foo(metaclass=SingletonType):
    def __init__(self,name):
        self.name = name
    def __new__(cls, *args, **kwargs):
        return object.__new__(cls, *args, **kwargs)
'''
    1、对象是类创建的，创建对象时类的__init__方法会自动执行，对象（）执行类的__call__方法
    2、类是type创建的，创建类时候type类的__init__方法会自动执行，类（）会先执行type的__call__方法（调用类的__new__，__init__方法）
    Foo 这个类是由SingletonType这个类创建的
'''
obj = Foo("hiayan")


# ============第三种方式实现单例模式=================
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)

import pymysql
import threading
from DBUtils.PooledDB import PooledDB

class SingletonDBPool(object):
    _instance_lock = threading.Lock()

    def __init__(self):
        self.pool = PooledDB(
            creator=pymysql,  # 使用链接数据库的模块
            maxconnections=6,  # 连接池允许的最大连接数，0和None表示不限制连接数
            mincached=2,  # 初始化时，链接池中至少创建的空闲的链接，0表示不创建

            maxcached=5,  # 链接池中最多闲置的链接，0和None不限制
            maxshared=3,
            # 链接池中最多共享的链接数量，0和None表示全部共享。PS: 无用，因为pymysql和MySQLdb等模块的 threadsafety都为1，所有值无论设置为多少，_maxcached永远为0，所以永远是所有链接都共享。
            blocking=True,  # 连接池中如果没有可用连接后，是否阻塞等待。True，等待；False，不等待然后报错
            maxusage=None,  # 一个链接最多被重复使用的次数，None表示无限制
            setsession=[],  # 开始会话前执行的命令列表。如：["set datestyle to ...", "set time zone ..."]
            ping=0,
            # ping MySQL服务端，检查是否服务可用。# 如：0 = None = never, 1 = default = whenever it is requested, 2 = when a cursor is created, 4 = when a query is executed, 7 = always
            host='127.0.0.1',
            port=3306,
            user='root',
            password='123',
            database='pooldb',
            charset='utf8'
        )

    def __new__(cls, *args, **kwargs):
        if not hasattr(SingletonDBPool, "_instance"):
            with SingletonDBPool._instance_lock:
                if not hasattr(SingletonDBPool, "_instance"):
                    SingletonDBPool._instance = object.__new__(cls, *args, **kwargs)
        return SingletonDBPool._instance

    def connect(self):
        return self.pool.connection()

from pool import SingletonDBPool

def run():
    pool = SingletonDBPool()
    conn = pool.connect()
    # xxxxxx
    cursor = conn.cursor()
    cursor.execute("select * from td where id=%s", [5, ])
    result = cursor.fetchall()  # 获取数据
    cursor.close()
    conn.close()

if __name__ == '__main__':
    run()

#
def wrapper(cls):
    instance = {}
    def inner(*args,**kwargs):
        if cls not in  instance:
            instance[cls] = cls(*args,**kwargs)
        return instance[cls]
    return inner

@wrapper
class Singleton(object):
    def __init__(self,name,age):
        self.name = name
        self.age = age

obj1 = Singleton('haiyan',22)
obj2 = Singleton('xx',22)
print(obj1)
print(obj2)