本地线程，隔离每个线程中间的数据
import threading
import time
local_values = threading.local()
def func(num):
local_values.name = num
time.sleep(2)
print(local_values.name, threading.current_thread().name)
for i in range(10):
t = threading.Thread(target=func, args=[i, ])
t.start()
local类实例化的对象是一个类似字典的结构
{
'identity': {'k1': 'v1', 'k2': ''v2},
'identity2': {'k1': 'v1', 'k2': ''v2},
...
}
源码
class _localimpl:
"""A class managing thread-local dicts"""
__slots__ = 'key', 'dicts', 'localargs', 'locallock', '__weakref__'
def __init__(self):
# The key used in the Thread objects' attribute dicts.
# We keep it a string for speed but make it unlikely to clash with
# a "real" attribute.
self.key = '_threading_local._localimpl.' + str(id(self))
# { id(Thread) -> (ref(Thread), thread-local dict) }
self.dicts = {}
def get_dict(self):
"""Return the dict for the current thread. Raises KeyError if none
defined."""
thread = current_thread()
return self.dicts[id(thread)][1]
def create_dict(self):
"""Create a new dict for the current thread, and return it."""
localdict = {}
key = self.key
thread = current_thread()
idt = id(thread)
def local_deleted(_, key=key):
# When the localimpl is deleted, remove the thread attribute.
thread = wrthread()
if thread is not None:
del thread.__dict__[key]
def thread_deleted(_, idt=idt):
# When the thread is deleted, remove the local dict.
# Note that this is suboptimal if the thread object gets
# caught in a reference loop. We would like to be called
# as soon as the OS-level thread ends instead.
local = wrlocal()
if local is not None:
dct = local.dicts.pop(idt)
wrlocal = ref(self, local_deleted)
wrthread = ref(thread, thread_deleted)
thread.__dict__[key] = wrlocal
self.dicts[idt] = wrthread, localdict
return localdict
class local:
# 定义类只能设置两个属性
__slots__ = '_local__impl', '__dict__'
def __new__(cls, *args, **kw):
if (args or kw) and (cls.__init__ is object.__init__):
raise TypeError("Initialization arguments are not supported")
self = object.__new__(cls)
# 设置类的_local__impl属性为一个_localimpl类的实例
impl = _localimpl()
impl.localargs = (args, kw)
impl.locallock = RLock()
object.__setattr__(self, '_local__impl', impl)
impl.create_dict()
return self
# 以下是一些常规的设置
def __getattribute__(self, name):
with _patch(self):
return object.__getattribute__(self, name)
def __setattr__(self, name, value):
if name == '__dict__':
raise AttributeError(
"%r object attribute '__dict__' is read-only"
% self.__class__.__name__)
with _patch(self):
return object.__setattr__(self, name, value)
def __delattr__(self, name):
if name == '__dict__':
raise AttributeError(
"%r object attribute '__dict__' is read-only"
% self.__class__.__name__)
with _patch(self):
return object.__delattr__(self, name)
连接池参数
from DBUtils.PooledDB import PooledDB, SharedDBConnection
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'
)
from DBUtils.PersistentDB import PersistentDB
import pymysql
POOL = PersistentDB(
creator=pymysql,
maxusage=None,
setsession=[],
ping=0,
cursor is created, 4 = when a query is executed, 7 = always
closeable=False,
threadlocal=None,
host='127.0.0.1',
port=3306,
user='root',
password='123',
database='pooldb',
charset='utf8'
)
def func():
# conn = SteadyDBConnection()
conn = POOL.connection()
cursor = conn.cursor()
cursor.execute('select * from tb1')
result = cursor.fetchall()
cursor.close()
conn.close() # 不是真的关闭，而是假的关闭。 conn = pymysql.connect() conn.close()
conn = POOL.connection()
cursor = conn.cursor()
cursor.execute('select * from tb1')
result = cursor.fetchall()
cursor.close()
conn.close()
import threading
for i in range(10):
t = threading.Thread(target=func)
t.start()
import time
import pymysql
import threading
from DBUtils.PooledDB import PooledDB, SharedDBConnection
POOL = PooledDB(
creator=pymysql,
maxconnections=6,
mincached=2,
maxcached=5,
maxshared=3,
blocking=True,
maxusage=None,
setsession=[],
ping=0,
host='127.0.0.1',
port=3306,
user='root',
password='123',
database='pooldb',
charset='utf8'
)
def func():
# 检测当前正在运行连接数的是否小于最大链接数，如果不小于则：等待或报raise TooManyConnections异常
# 否则
# 则优先去初始化时创建的链接中获取链接 SteadyDBConnection。
# 然后将SteadyDBConnection对象封装到PooledDedicatedDBConnection中并返回。
# 如果最开始创建的链接没有链接，则去创建一个SteadyDBConnection对象，再封装到PooledDedicatedDBConnection中并返回。
# 一旦关闭链接后，连接就返回到连接池让后续线程继续使用。
# PooledDedicatedDBConnection
conn = POOL.connection()
# print(th, '链接被拿走了', conn1._con)
# print(th, '池子里目前有', pool._idle_cache, '\r\n')
cursor = conn.cursor()
cursor.execute('select * from tb1')
result = cursor.fetchall()
conn.close()
conn = POOL.connection()
# print(th, '链接被拿走了', conn1._con)
# print(th, '池子里目前有', pool._idle_cache, '\r\n')
cursor = conn.cursor()
cursor.execute('select * from tb1')
result = cursor.fetchall()
conn.close()
func()