Question

我正在尝试在Python中使用带有多处理库的队列。执行下面的代码后（打印语句工作），但是我在队列上调用join后进程没有退出并且仍然存在。如何终止剩余的流程？

谢谢！

def MultiprocessTest(self):
  print "Starting multiprocess."
  print "Number of CPUs",multiprocessing.cpu_count()

  num_procs = 4
  def do_work(message):
    print "work",message ,"completed"

  def worker():
    while True:
      item = q.get()
      do_work(item)
      q.task_done()

  q = multiprocessing.JoinableQueue()
  for i in range(num_procs):
    p = multiprocessing.Process(target=worker)
    p.daemon = True
    p.start()

  source = ['hi','there','how','are','you','doing']
  for item in source:
    q.put(item)
  print "q close"
  q.join()
  #q.close()
  print "Finished everything...."
  print "num active children:",multiprocessing.active_children()

Answer 1

试试这个：

import multiprocessing

num_procs = 4
def do_work(message):
  print "work",message ,"completed"

def worker():
  for item in iter( q.get, None ):
    do_work(item)
    q.task_done()
  q.task_done()

q = multiprocessing.JoinableQueue()
procs = []
for i in range(num_procs):
  procs.append( multiprocessing.Process(target=worker) )
  procs[-1].daemon = True
  procs[-1].start()

source = ['hi','there','how','are','you','doing']
for item in source:
  q.put(item)

q.join()

for p in procs:
  q.put( None )

q.join()

for p in procs:
  p.join()

print "Finished everything...."
print "num active children:", multiprocessing.active_children()

Answer 2

你的工人需要一个哨兵来终止，否则他们只会坐在封锁读物上。请注意，使用Q上的睡眠而不是P上的连接可以显示状态信息等我首选的模板是：

def worker(q,nameStr):
  print 'Worker %s started' %nameStr
  while True:
     item = q.get()
     if item is None: # detect sentinel
       break
     print '%s processed %s' % (nameStr,item) # do something useful
     q.task_done()
  print 'Worker %s Finished' % nameStr
  q.task_done()

q = multiprocessing.JoinableQueue()
procs = []
for i in range(num_procs):
  nameStr = 'Worker_'+str(i)
  p = multiprocessing.Process(target=worker, args=(q,nameStr))
  p.daemon = True
  p.start()
  procs.append(p)

source = ['hi','there','how','are','you','doing']
for item in source:
  q.put(item)

for i in range(num_procs):
  q.put(None) # send termination sentinel, one for each process

while not q.empty(): # wait for processing to finish
  sleep(1)   # manage timeouts and status updates etc.

Answer 3

您必须在加入流程之前清除队列，但q.empty（）不可靠。

清除队列的最佳方法是计算成功获取或循环的次数，直到收到哨兵值，就像具有可靠网络的套接字一样。

Answer 4

下面的代码可能不太相关，但我会将其发布给您的评论/反馈，以便我们可以一起学习。谢谢！

import multiprocessing

def boss(q,nameStr):
  source = range(1024)
  for item in source:
    q.put(nameStr+' '+str(item))
  q.put(None) # send termination sentinel, one for each process

def worker(q,nameStr):
  while True:
     item = q.get()
     if item is None: # detect sentinel
       break
     print '%s processed %s' % (nameStr,item) # do something useful

q = multiprocessing.Queue()

procs = []

num_procs = 4
for i in range(num_procs):
  nameStr = 'ID_'+str(i)
  p = multiprocessing.Process(target=worker, args=(q,nameStr))
  procs.append(p)
  p = multiprocessing.Process(target=boss,   args=(q,nameStr))
  procs.append(p)

for j in procs:
  j.start()
for j in procs:
  j.join()

Answer 5

这是一个 sentinel-free 方法，用于相对简单的情况，您在JoinableQueue上放置了许多任务，然后启动消耗任务的工作进程并在读取后退出队列“干”。诀窍是使用JoinableQueue.get_nowait()而不是get()。顾名思义，get_nowait()尝试以非阻塞方式从队列中获取值，如果没有任何东西可以获取，则会引发queue.Empty异常。该工作者通过退出来处理此异常。

说明原则的基本代码：

import multiprocessing as mp
from queue import Empty

def worker(q):
  while True:
    try:
      work = q.get_nowait()
      # ... do something with `work`
      q.task_done()
    except Empty:
      break # completely done

# main
worknum = 4
jq = mp.JoinableQueue()

# fill up the task queue
# let's assume `tasks` contains some sort of data
# that your workers know how to process
for task in tasks:
  jq.put(task)

procs = [ mp.Process(target=worker, args=(jq,)) for _ in range(worknum) ]
for p in procs:
  p.start()

for p in procs:
  p.join()

优点是您不需要将“毒丸”放在队列中，因此代码会更短。

重要：在生产者和消费者以“交错”方式使用相同队列的更复杂情况下，工作人员可能不得不等待新任务出现，应该使用“毒丸”方法。我上面的建议是针对简单的情况，工人们“知道”如果任务队列是空的，那么就没有任何意义了。

Python中的多处理队列

5 个答案: