# coding:utf-8
import threading

import pymysql
from DBUtils.PooledDB import PooledDB

from app.common.file_config import get_config


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

    def __init__(self):
        if not hasattr(DbPool, "pool"):
            DbPool.mysql_pool()
        
 
else:
            pass

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

    @staticmethod
    
 
def mysql_pool():
        host = get_config(‘database‘, ‘MYSQL_HOST‘)
        port = int(get_config(‘database‘, ‘MYSQL_PORT‘))
        user = get_config(‘database‘, ‘MYSQL_USERNAME‘)
        passwd = get_config(‘database‘, ‘MYSQL_PASSWORD‘)
        db = get_config(‘database‘, ‘MYSQL_DB‘)
        DbPool.pool 
 
= PooledDB(
            creator=pymysql,  # 使用鏈接數據庫的模塊
            mincached=2,  # 初始化時，鏈接池中至少創建的空閑的鏈接，0表示不創建
            maxcached=6,  # 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，所有值無論設置為多少，_maxcached永遠為0，所以永遠是所有鏈接都共享。
            maxconnections=8,  # 連接池允許的最大連接數，0和None表示不限制連接數
            blocking=True,  # 連接池中如果沒有可用連接後，是否阻塞等待。True，等待；False，不等待然後報錯
            maxusage=None,  # 一個鏈接最多被重復使用的次數，None表示無限制
            setsession=None,  # 開始會話前執行的命令列表。如：["set datestyle to ...", "set time zone ..."]
            # ping MySQL服務端，檢查是否服務可用。# 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=host,
            port=port,
            user=user,
            passwd=passwd,
            db=db,
            use_unicode=False,
            charset=‘utf8‘
        )

Python下Mysql數據連接池——單例