Worth Waiting For

單利

s1.py

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

v = Foo()
#v是Foo的實例

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

# 兩個的內(nèi)存地址是一樣的
# 文件加載的時候，第一次導(dǎo)入后，再次導(dǎo)入時不會再重新加載。

# ======================單例模式：無法支持多線程情況===============

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()


# ====================單例模式：支持多線程情況================、

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:   #為了保證線程安全在內(nèi)部加鎖
                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)

# 使用先說明，以后用單例模式，obj = Singleton.instance()
# 示例：
# obj1 = Singleton.instance()
# obj2 = Singleton.instance()
# print(obj1,obj2)
# 錯誤示例
# obj1 = Singleton()
# obj2 = Singleton()
# print(obj1,obj2)

# =============單線程下執(zhí)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"):
                    # 類加括號就回去執(zhí)行__new__方法，__new__方法會創(chuàng)建一個類實例：Singleton()
                    Singleton._instance = object.__new__(cls)  # 繼承object類的__new__方法，類去調(diào)用方法，說明是函數(shù)，要手動傳cls
        return Singleton._instance  #obj1
        #類加括號就會先去執(zhí)行__new__方法，在執(zhí)行__init__方法
# obj1 = Singleton()
# obj2 = Singleton()
# print(obj1,obj2)

# ===========多線程執(zhí)行單利============
def task(arg):
    obj = Singleton()
    print(obj)

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

# 使用先說明，以后用單例模式，obj = Singleton()
# 示例
# obj1 = Singleton()
# obj2 = Singleton()
# print(obj1,obj2)

"""
1.對象是類創(chuàng)建，創(chuàng)建對象時候類的__init__方法自動執(zhí)行，對象()執(zhí)行類的 __call__ 方法
2.類是type創(chuàng)建，創(chuàng)建類時候type的__init__方法自動執(zhí)行，類() 執(zhí)行type的 __call__方法(類的__new__方法,類的__init__方法)

# 第0步: 執(zhí)行type的 __init__ 方法【類是type的對象】
class Foo:
    def __init__(self):
        pass

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

# 第1步: 執(zhí)行type的 __call__ 方法
#        1.1  調(diào)用 Foo類（是type的對象）的 __new__方法，用于創(chuàng)建對象。
#        1.2  調(diào)用 Foo類（是type的對象）的 __init__方法，用于對對象初始化。
obj = Foo()
# 第2步：執(zhí)行Foo的 __call__ 方法
obj()
"""

# ===========類的執(zhí)行流程================
class SingletonType(type):
    def __init__(self,*args,**kwargs):
        print(self)  #會不會打印？  #<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、對象是類創(chuàng)建的，創(chuàng)建對象時類的__init__方法會自動執(zhí)行，對象（）執(zhí)行類的__call__方法
    2、類是type創(chuàng)建的，創(chuàng)建類時候type類的__init__方法會自動執(zhí)行，類（）會先執(zhí)行type的__call__方法（調(diào)用類的__new__，__init__方法）
    Foo 這個類是由SingletonType這個類創(chuàng)建的
'''
obj = Foo("hiayan")


# ============第三種方式實現(xiàn)單例模式=================
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,  # 使用鏈接數(shù)據(jù)庫的模塊
            maxconnections=6,  # 連接池允許的最大連接數(shù)，0和None表示不限制連接數(shù)
            mincached=2,  # 初始化時，鏈接池中至少創(chuàng)建的空閑的鏈接，0表示不創(chuàng)建

            maxcached=5,  # 鏈接池中最多閑置的鏈接，0和None不限制
            maxshared=3,
            # 鏈接池中最多共享的鏈接數(shù)量，0和None表示全部共享。PS: 無用，因為pymysql和MySQLdb等模塊的 threadsafety都為1，所有值無論設(shè)置為多少，_maxcached永遠為0，所以永遠是所有鏈接都共享。
            blocking=True,  # 連接池中如果沒有可用連接后，是否阻塞等待。True，等待；False，不等待然后報錯
            maxusage=None,  # 一個鏈接最多被重復(fù)使用的次數(shù)，None表示無限制
            setsession=[],  # 開始會話前執(zhí)行的命令列表。如：["set datestyle to ...", "set time zone ..."]
            ping=0,
            # ping MySQL服務(wù)端，檢查是否服務(wù)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()  # 獲取數(shù)據(jù)
    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)