解析python 生产/消费者模型实现过程
1.多线程实现
import threading
import queue
import logging
logging.basicConfig(level = logging.INFO,format = '%(asctime)s - %(levelname)s -->%(funcName)s at line %(lineno)d: \n %(message)s')
log= logging.getLogger() def producer(q):
for k in range(10):
q.put(k)
logging.info("put %s item into queue "%k)
# block all producer main until consumer get all queue members that put
q.join() def consumer(q):
while True:
"""
if queue been empty and q.get(block=True),
because default block in source code is True ,
queue will bock forever util queue put new item .
"""
item=q.get()
logging.info("get out of %s member of queue "%item) # notify q.join() consumer has get out of member of queue
q.task_done() if __name__ == '__main__':
thread_num=5
# limit max length of queue
q = queue.Queue(maxsize=5)
producers=[threading.Thread(target=producer,args=(q,))]
consumers=[threading.Thread(target=consumer,args=(q,)) for i in range(thread_num)]
# start producer and consumer
for pr in producers:
pr.start()
for cn in consumers:
cn.start()
# block main thread of producer
for p in producers:
p.join()
# block main of consumer
for c in consumers:
c.join() 执行结果:可以看到控制台一直阻塞在那里。由于消费者消费完queue里面所有的成员后queue 变成empty,空队列,由于源码q.get()内置参数block一直为True,当取不到时一直阻塞,那么这就意味着当你block 为True时必须设置结束标志让消费者结束,退出死循环接下来我们
改良一下这个方法:
在生产者生产的时候加入结束标志None告诉消费者拿到None时就break 跳出死循环,结束消费,这样就解决了消费之一直阻塞问题:
在producer主线程join之前添加与线程数目相同的None,让每个thread break 跳出死循环:
import threading
import queue
import logging
logging.basicConfig(level = logging.INFO,format = '%(asctime)s - %(levelname)s -->%(funcName)s at line %(lineno)d: \n %(message)s')
log= logging.getLogger() def producer(q):
for k in range(10):
q.put(k)
logging.info("put %s item into queue "%k)
# block all producer main until consumer get all queue members that put
q.join() def consumer(q):
while True:
"""
if queue been empty and q.get(block=True),
because default block in source code is True ,
queue will bock forever util queue put new item .
"""
item=q.get()
logging.info("get out of %s member of queue " % item)
if item == None:
logging.info("get None stop consumer from while loop")
break
# notify q.join() consumer has get out of member of queue
q.task_done() if __name__ == '__main__':
thread_num=5
# limit max length of queue
q = queue.Queue(maxsize=5)
producers=[threading.Thread(target=producer,args=(q,))]
consumers=[threading.Thread(target=consumer,args=(q,)) for i in range(thread_num)]
# start producer and consumer
for pr in producers:
pr.start()
for cn in consumers:
cn.start()
# block main thread of producer
for p in producers:
p.join()
# put same number of thread_num None to break thread from consumer while
for i in range(thread_num):
q.put(None)
# block main of consumer
for c in consumers:
c.join()
2019-12-21 20:37:00,206 - INFO -->consumer at line 23:
get out of None member of queue
2019-12-21 20:37:00,206 - INFO -->consumer at line 25:
get None mean break
2019-12-21 20:37:00,206 - INFO -->consumer at line 25:
get None mean break
2019-12-21 20:37:00,206 - INFO -->consumer at line 25:
get None mean break
2019-12-21 20:37:00,206 - INFO -->consumer at line 25:
get None mean break
2019-12-21 20:37:00,206 - INFO -->consumer at line 23:
get out of None member of queue
2019-12-21 20:37:00,207 - INFO -->consumer at line 25:
get None mean break
Process finished with exit code 0
结果:正常释放所有线程,但是好像每次线程都要加个标志太麻烦,感觉,能不能有更好的办法呢,当然接着往下看:
改良consumer方法在每次消费队列之前检查队列queue.empty() 是否为True,是就直接break跳出while loop:就不需要每次都加None标志了
import threading
import queue
import logging
logging.basicConfig(level = logging.INFO,format = '%(asctime)s - %(levelname)s -->%(funcName)s at line %(lineno)d: \n %(message)s')
log= logging.getLogger() def producer(q):
for k in range(10):
q.put(k)
logging.info("put %s item into queue "%k)
# block all producer main until consumer get all queue members that put
q.join() def consumer(q):
while True:
"""
if queue been empty and q.get(block=True),
because default block in source code is True ,
queue will bock forever util queue put new item .
"""
if q.empty():break
item=q.get()
logging.info("get out of %s member of queue " % item)
# notify q.join() consumer has get out of member of queue
q.task_done() if __name__ == '__main__':
thread_num=5
# limit max length of queue
q = queue.Queue(maxsize=5)
producers=[threading.Thread(target=producer,args=(q,))]
consumers=[threading.Thread(target=consumer,args=(q,)) for i in range(thread_num)]
# start producer and consumer
for pr in producers:
pr.start()
for cn in consumers:
cn.start()
# block main thread of producer
for p in producers:
p.join()
j结果如下:
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