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Python之多线程：线程互斥与线程同步

2024-10-31 19:27:39   205人阅读

一、锁在多线程中的使用：线程互斥
lock = threading.Lock()#创建一个锁对象
1、with lock:
pass
和进程使用的方式相同
 
2、控制线程结束的时间
通过一个全局变量
# encoding=utf-8
import threading,time,Queue,random
 
exitFlag = False
def write(lock,queue):
while exitFlag != True:
with lock:
data = http://www.mamicode.com/random.randint(1,100)
print ‘put:‘,data
queue.put(data)
time.sleep(1)
 
def read(queue):
while exitFlag != True:
print ‘get:‘,queue.get()
time.sleep(1)
 
if __name__ == ‘__main__‘:
lock = threading.Lock()
queue = Queue.Queue()
t1 = threading.Thread(target=write,args=(lock,queue))
t2 = threading.Thread(target=write,args=(lock,queue))
t3 = threading.Thread(target=read,args=(queue,))
t1.start()
t2.start()
t3.start()
time.sleep(10)
exitFlag = True
t1.join()
t2.join()
t3.join()
 
二、线程同步
1、生产者--消费者模式
Queue() 作为生产者和消费者的中介
from
 
class Producer(threading.Thread):
def __init__(self,t_name,queue):
threading.Thread.__init__(self,name=t_name)#继承父类的构造方法的目的：初始化一些线程实例，
self.data=http://www.mamicode.com/queue
def run(self):
for i in xrange(5):
print ‘%s:%s is producing %d to the queue\n‘%(time.ctime(),self.getname(),i)
self.data.put(i)
time.sleep(2)
print ‘%s:%s put finished \n‘%(time.ctime(),self.getname(),i)
def Consumer(threading.Thread):
def __init__(self,t_name,queue):
threading.Thread.__init__(self,name=t_name)
self.data=http://www.mamicode.com/queue
def run(self):
for i in xrange(5):
val=self.data.get()
print ‘%s:%s is consumer %d in the queue\n‘%(time.ctime(),self.getname(),val)
print ‘%s:%s consumer finished \n‘%(time.ctime(),self.getname(),i)
 
if __name==‘__main__‘:
queue=Queue()#没有制定队列大小，默认为无限大，可以不受限制的放入队列
producer=Producer(‘Pro‘,queue)
consumer=Consumer(‘Con‘,queue)
producer.start()
time.sleep(1)
consumer.start()
producer.join()
consumer.join()
print ‘mainThread end‘
 
2、Event 信号传递
event=threading.Event()
import threading,time,Queue,random
 
def write(lock,queue,event):
while not event.isSet():
with lock:
thread = threading.currentThread()
data = http://www.mamicode.com/random.randint(1,100)
print ‘this is thread:‘,thread.getName(),‘put:‘,data
queue.put(data)
time.sleep(1)
 
def read(queue):
while not event.isSet():
print ‘get:‘,queue.get()
time.sleep(1)
 
if __name__ == ‘__main__‘:
lock = threading.Lock()
queue = Queue.Queue()
event=threading.Event()
t1 = threading.Thread(target=write,args=(lock,queue,event))
t2 = threading.Thread(target=write,args=(lock,queue,event))
t3 = threading.Thread(target=read,args=(queue,))
t1.start()
t2.start()
t3.start()
time.sleep(10)
event.set()
t1.join()
t2.join()
t3.join()
3、lock :只能加一把锁
4、semaphore：可以加多把锁
设置限制最多3个线程同时访问共享资源：s = threading.Semaphore(3)
5、event:线程等待某一时间的发生，之后执行逻辑
6、Condition 条件
con=threading.Condition()
使用场景：处理复杂的逻辑。基于锁来实现的
两个线程之间做一些精准的通信
线程A做了某一件事，中途需要停止
线程B做另外一件事情，线程B通知线程A
线程A继续
（1）额外提供了wait()方法和notify()方法，用于处理复杂的逻辑
（2）wait()释放锁，并且等待通知
（3）Notify（）唤醒对方，可以继续下去。但是需要两个线程之间需要抢锁，谁抢到执行谁
通过（2）和（3），实现线程间的通信。
import threading
import time
product = 0
exitFlag = False
def consumer(con):
global product
while exitFlag != True:
with con:
print ‘enter consummer thread‘
if product == 0:
con.wait()
else:
print ‘now consummer 1 product‘
product -= 1
print ‘after consummer, we have ‘,product,‘product now‘
time.sleep(2)
 
def producer(con):
global product
while exitFlag != True:
with con:
print ‘enter producer thread‘
product += 1
con.notify()
print ‘after producer, we have ‘, product, ‘product now‘
time.sleep(2)
 
if __name__ == ‘__main__‘:
con = threading.Condition()
c1 = threading.Thread(target=consumer,args=(con,))
p1 = threading.Thread(target=producer, args=(con,))
 
c1.start()
p1.start()
time.sleep(6)
exitFlag = True
c1.join()
p1.join()
 
7、死锁
t1:拥有lock1锁，申请lock2锁
t2:拥有lock2锁，申请lock1锁
（1）如何尽量的保证不出现死锁：
定义锁的使用顺序

Python之多线程：线程互斥与线程同步


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