# -*- coding: utf-8 -*-

import time
from Queue import Queue

class PoolException(Exception):
    pass

class Pool(object):
    '''一个数据库连接池'''
    def __init__(self, maxActive=5, maxWait=None, init_size=0, db_type="SQLite3", **config):
        self.__freeConns = Queue(maxActive)
        self.maxWait = maxWait
        self.db_type = db_type
        self.config = config
        if init_size > maxActive:
            init_size = maxActive
        for i in range(init_size):
            self.free(self._create_conn())
    
    def __del__(self):
        print("__del__ Pool..")
        self.release()
    
    def release(self):
        '''释放资源，关闭池中的所有连接'''
        print("release Pool..")
        while self.__freeConns and not self.__freeConns.empty():
            con = self.get()
            con.release()
        self.__freeConns = None
 
    def _create_conn(self):
        '''创建连接 '''
        if self.db_type in dbcs:
            return dbcs[self.db_type](**self.config);
        
    def get(self, timeout=None):
        '''获取一个连接
        @param timeout:超时时间
        '''
        if timeout is None:
            timeout = self.maxWait
        conn = None
        if self.__freeConns.empty():#如果容器是空的，直接创建一个连接
            conn = self._create_conn()
        else:
            conn = self.__freeConns.get(timeout=timeout)
        conn.pool = self
        return conn
    
    def free(self, conn):
        '''将一个连接放回池中
        @param conn: 连接对象
        '''
        conn.pool = None
        if(self.__freeConns.full()):#如果当前连接池已满，直接关闭连接
            conn.release()
            return
        self.__freeConns.put_nowait(conn)

from abc import ABCMeta, abstractmethod

class PoolingConnection(object):
    def __init__(self, **config):
        self.conn = None
        self.config = config
        self.pool = None
        
    def __del__(self):
        self.release()
        
    def __enter__(self):
        pass
    
    def __exit__(self, exc_type, exc_value, traceback):
        self.close()
        
    def release(self):
        print("release PoolingConnection..")
        if self.conn is not None:
            self.conn.close()
            self.conn = None
        self.pool = None
            
    def close(self):
        if self.pool is None:
            raise PoolException("连接已关闭")
        self.pool.free(self)
        
    def __getattr__(self, val):
        if self.conn is None and self.pool is not None:
            self.conn = self._create_conn(**self.config)
        if self.conn is None:
            raise PoolException("无法创建数据库连接 或连接已关闭")
        return getattr(self.conn, val)
 
    @abstractmethod
    def _create_conn(self, **config):
        pass

class SQLit3PoolConnection(PoolingConnection):
    def _create_conn(self, **config):
        import sqlite3
        return sqlite3.connect(**config)
 
dbcs = {"SQLite3": SQLit3PoolConnection}
 
pool = Pool(database="test\\a")

def test():
    conn = pool.get()
    with conn:
        for a in conn.execute("SELECT * FROM A"):
            print(a)
 
if __name__ == "__main__":
    test()