举例讲解Python编程中对线程锁的使用


Posted in Python onJuly 12, 2016

python的内置数据结构比如列表和字典等是线程安全的,但是简单数据类型比如整数和浮点数则不是线程安全的,要这些简单数据类型的通过操作,就需要使用锁。

#!/usr/bin/env python3
# coding=utf-8

import threading

shared_resource_with_lock = 0
shared_resource_with_no_lock = 0
COUNT = 100000
shared_resource_lock = threading.Lock()

####LOCK MANAGEMENT##
def increment_with_lock():
  global shared_resource_with_lock
  for i in range(COUNT):
    shared_resource_lock.acquire()
    shared_resource_with_lock += 1
    shared_resource_lock.release()
    
def decrement_with_lock():
  global shared_resource_with_lock
  for i in range(COUNT):
    shared_resource_lock.acquire()
    shared_resource_with_lock -= 1
    shared_resource_lock.release()
    ####NO LOCK MANAGEMENT ##
  
def increment_without_lock():
  global shared_resource_with_no_lock
  for i in range(COUNT):
    shared_resource_with_no_lock += 1
  
def decrement_without_lock():
  global shared_resource_with_no_lock
  for i in range(COUNT):
    shared_resource_with_no_lock -= 1
  
####the Main program
if __name__ == "__main__":
  t1 = threading.Thread(target = increment_with_lock)
  t2 = threading.Thread(target = decrement_with_lock)
  t3 = threading.Thread(target = increment_without_lock)
  t4 = threading.Thread(target = decrement_without_lock)
  t1.start()
  t2.start()
  t3.start()
  t4.start()
  t1.join()
  t2.join()
  t3.join()
  t4.join()
  print ("the value of shared variable with lock management is %s"\
  %shared_resource_with_lock)
  print ("the value of shared variable with race condition is %s"\
  %shared_resource_with_no_lock)

执行结果:

$ ./threading_lock.py
the value of shared variable with lock management is 0
the value of shared variable with race condition is 0

又如:

import random
import threading
import time
logging.basicConfig(level=logging.DEBUG,
          format='(%(threadName)-10s) %(message)s',
          )
          
class Counter(object):
  def __init__(self, start=0):
    self.lock = threading.Lock()
    self.value = start
  def increment(self):
    logging.debug(time.ctime(time.time()))
    logging.debug('Waiting for lock')
    self.lock.acquire()
    try:
      pause = random.randint(1,3)
      logging.debug(time.ctime(time.time()))
      logging.debug('Acquired lock')      
      self.value = self.value + 1
      logging.debug('lock {0} seconds'.format(pause))
      time.sleep(pause)
    finally:
      self.lock.release()
def worker(c):
  for i in range(2):
    pause = random.randint(1,3)
    logging.debug(time.ctime(time.time()))
    logging.debug('Sleeping %0.02f', pause)
    time.sleep(pause)
    c.increment()
  logging.debug('Done')
counter = Counter()
for i in range(2):
  t = threading.Thread(target=worker, args=(counter,))
  t.start()
logging.debug('Waiting for worker threads')
main_thread = threading.currentThread()
for t in threading.enumerate():
  if t is not main_thread:
    t.join()
logging.debug('Counter: %d', counter.value)

执行结果:

$ python threading_lock.py
(Thread-1 ) Tue Sep 15 15:49:18 2015
(Thread-1 ) Sleeping 3.00
(Thread-2 ) Tue Sep 15 15:49:18 2015
(MainThread) Waiting for worker threads
(Thread-2 ) Sleeping 2.00
(Thread-2 ) Tue Sep 15 15:49:20 2015
(Thread-2 ) Waiting for lock
(Thread-2 ) Tue Sep 15 15:49:20 2015
(Thread-2 ) Acquired lock
(Thread-2 ) lock 2 seconds
(Thread-1 ) Tue Sep 15 15:49:21 2015
(Thread-1 ) Waiting for lock
(Thread-2 ) Tue Sep 15 15:49:22 2015
(Thread-1 ) Tue Sep 15 15:49:22 2015
(Thread-2 ) Sleeping 2.00
(Thread-1 ) Acquired lock
(Thread-1 ) lock 1 seconds
(Thread-1 ) Tue Sep 15 15:49:23 2015
(Thread-1 ) Sleeping 2.00
(Thread-2 ) Tue Sep 15 15:49:24 2015
(Thread-2 ) Waiting for lock
(Thread-2 ) Tue Sep 15 15:49:24 2015
(Thread-2 ) Acquired lock
(Thread-2 ) lock 1 seconds
(Thread-1 ) Tue Sep 15 15:49:25 2015
(Thread-1 ) Waiting for lock
(Thread-1 ) Tue Sep 15 15:49:25 2015
(Thread-1 ) Acquired lock
(Thread-1 ) lock 2 seconds
(Thread-2 ) Done
(Thread-1 ) Done
(MainThread) Counter: 4

acquire()中传入False值,可以检查是否获得了锁。比如:

import logging
import threading
import time
logging.basicConfig(level=logging.DEBUG,
          format='(%(threadName)-10s) %(message)s',
          )
          
def lock_holder(lock):
  logging.debug('Starting')
  while True:
    lock.acquire()
    try:
      logging.debug('Holding')
      time.sleep(0.5)
    finally:
      logging.debug('Not holding')
      lock.release()
    time.sleep(0.5)
  return
          
def worker(lock):
  logging.debug('Starting')
  num_tries = 0
  num_acquires = 0
  while num_acquires < 3:
    time.sleep(0.5)
    logging.debug('Trying to acquire')
    have_it = lock.acquire(0)
    try:
      num_tries += 1
      if have_it:
        logging.debug('Iteration %d: Acquired',
               num_tries)
        num_acquires += 1
      else:
        logging.debug('Iteration %d: Not acquired',
               num_tries)
    finally:
      if have_it:
        lock.release()
  logging.debug('Done after %d iterations', num_tries)
lock = threading.Lock()
holder = threading.Thread(target=lock_holder,
             args=(lock,),
             name='LockHolder')
holder.setDaemon(True)
holder.start()
worker = threading.Thread(target=worker,
             args=(lock,),
             name='Worker')
worker.start()

执行结果:

$ python threading_lock_noblock.py
(LockHolder) Starting
(LockHolder) Holding
(Worker  ) Starting
(LockHolder) Not holding
(Worker  ) Trying to acquire
(Worker  ) Iteration 1: Acquired
(LockHolder) Holding
(Worker  ) Trying to acquire
(Worker  ) Iteration 2: Not acquired
(LockHolder) Not holding
(Worker  ) Trying to acquire
(Worker  ) Iteration 3: Acquired
(LockHolder) Holding
(Worker  ) Trying to acquire
(Worker  ) Iteration 4: Not acquired
(LockHolder) Not holding
(Worker  ) Trying to acquire
(Worker  ) Iteration 5: Acquired
(Worker  ) Done after 5 iterations

线程安全锁

threading.RLock()

返回可重入锁对象。重入锁必须由获得它的线程释放。一旦线程获得了重入锁,同一线程可不阻塞地再次获得,获取之后必须释放。

通常一个线程只能获取一次锁:

import threading

lock = threading.Lock()

print 'First try :', lock.acquire()
print 'Second try:', lock.acquire(0)

执行结果:

$ python threading_lock_reacquire.py
First try : True
Second try: False

使用RLock可以获取多次锁:

import threading
lock = threading.RLock()
print 'First try :', lock.acquire()
print 'Second try:', lock.acquire(0)

执行结果:

python threading_rlock.py
First try : True
Second try: 1

再来看一个例子:

#!/usr/bin/env python3
# coding=utf-8
import threading
import time
class Box(object):
  lock = threading.RLock()
  def __init__(self):
    self.total_items = 0
  def execute(self,n):
    Box.lock.acquire()
    self.total_items += n
    Box.lock.release()
  def add(self):
    Box.lock.acquire()
    self.execute(1)
    Box.lock.release()
  def remove(self):
    Box.lock.acquire()
    self.execute(-1)
    Box.lock.release()
    
## These two functions run n in separate
## threads and call the Box's methods    
def adder(box,items):
  while items > 0:
    print ("adding 1 item in the box\n")
    box.add()
    time.sleep(5)
    items -= 1
    
def remover(box,items):
  while items > 0:
    print ("removing 1 item in the box")
    box.remove()
    time.sleep(5)
    items -= 1
    
## the main program build some
## threads and make sure it works
if __name__ == "__main__":
  items = 5
  print ("putting %s items in the box " % items)
  box = Box()
  t1 = threading.Thread(target=adder,args=(box,items))
  t2 = threading.Thread(target=remover,args=(box,items))
  t1.start()
  t2.start()
  t1.join()
  t2.join()
  print ("%s items still remain in the box " % box.total_items)

执行结果:

$ python3 threading_rlock2.py
putting 5 items in the box 
adding 1 item in the box
removing 1 item in the box
adding 1 item in the box
removing 1 item in the box
adding 1 item in the box
removing 1 item in the box
removing 1 item in the box
adding 1 item in the box
removing 1 item in the box
adding 1 item in the box
0 items still remain in the box
Python 相关文章推荐
一篇不错的Python入门教程
Feb 08 Python
Python实现国外赌场热门游戏Craps(双骰子)
Mar 31 Python
Python获取系统默认字符编码的方法
Jun 04 Python
在Python的Django框架中创建语言文件
Jul 27 Python
详解Python中for循环是如何工作的
Jun 30 Python
Python基于PyGraphics包实现图片截取功能的方法
Dec 21 Python
Python cookbook(数据结构与算法)从序列中移除重复项且保持元素间顺序不变的方法
Mar 13 Python
用python做游戏的细节详解
Jun 25 Python
如何将你的应用迁移到Python3的三个步骤
Dec 22 Python
python使用pandas抽样训练数据中某个类别实例
Feb 28 Python
Python爬虫requests库多种用法实例
May 28 Python
查找适用于matplotlib的中文字体名称与实际文件名对应关系的方法
Jan 05 Python
使用Python编写一个最基础的代码解释器的要点解析
Jul 12 #Python
Python中使用bidict模块双向字典结构的奇技淫巧
Jul 12 #Python
Python使用SocketServer模块编写基本服务器程序的教程
Jul 12 #Python
使用Python的Flask框架表单插件Flask-WTF实现Web登录验证
Jul 12 #Python
Python的Flask框架标配模板引擎Jinja2的使用教程
Jul 12 #Python
深度定制Python的Flask框架开发环境的一些技巧总结
Jul 12 #Python
Python的面向对象编程方式学习笔记
Jul 12 #Python
You might like
php学习笔记之 函数声明(二)
2011/06/09 PHP
ThinkPHP3.1新特性之命名范围的使用
2014/06/19 PHP
Thinkphp框架开发移动端接口(2)
2016/08/18 PHP
详解PHP序列化和反序列化原理
2018/01/15 PHP
CI框架实现创建自定义类库的方法
2018/12/25 PHP
JavaScript中for-in遍历方式示例介绍
2014/02/11 Javascript
ECMAScript5(ES5)中bind方法使用小结
2015/05/07 Javascript
如何使用jquery easyui创建标签组件
2015/11/18 Javascript
js类式继承与原型式继承详解
2016/04/07 Javascript
Javascript闭包与函数柯里化浅析
2016/06/22 Javascript
JavaScript判断数组是否存在key的简单实例
2016/08/03 Javascript
浅谈js中字符和数组一些基本算法题
2016/08/15 Javascript
jQuery事件处理的特征(事件命名机制)
2016/08/23 Javascript
微信小程序 wxapp视图容器 view详解
2016/10/31 Javascript
jQuery中Datatables增加跳转到指定页功能
2017/02/08 Javascript
vue proxyTable 接口跨域请求调试的示例
2017/09/12 Javascript
vue.js,ajax渲染页面的实例
2018/02/11 Javascript
javascript利用键盘控制小方块的移动
2020/04/20 Javascript
[10:18]2018DOTA2国际邀请赛寻真——找回自信的TNCPredator
2018/08/13 DOTA
零基础写python爬虫之爬虫的定义及URL构成
2014/11/04 Python
编写Python脚本来实现最简单的FTP下载的教程
2015/05/04 Python
图文详解WinPE下安装Python
2016/05/17 Python
python3实现基于用户的协同过滤
2018/05/31 Python
完美解决安装完tensorflow后pip无法使用的问题
2018/06/11 Python
手把手教你使用Python创建微信机器人
2019/04/29 Python
python:按行读入,排序然后输出的方法
2019/07/20 Python
CSS3+js实现简单的时钟特效
2015/03/18 HTML / CSS
科颜氏加拿大官方网站: Kiehl’s加拿大
2016/08/16 全球购物
将世界上最美丽的摄影作品转化为艺术作品:Photos.com
2017/11/28 全球购物
英国时尚运动品牌的合集:The Sports Edit
2017/12/20 全球购物
乌克兰机票、铁路和巴士票、酒店搜索、保险:Tickets.ua
2020/01/11 全球购物
SQL Server里面什么样的视图才能创建索引
2015/04/17 面试题
市级三好生竞选稿
2015/11/21 职场文书
《和时间赛跑》读后感3篇
2019/12/16 职场文书
python办公自动化之excel的操作
2021/05/23 Python
go使用Gin框架利用阿里云实现短信验证码功能
2021/08/04 Golang