Need for while True:
I don't understand why "while True:" is needed in below example
import os
import sys
import subprocess
imp开发者_Go百科ort time
from threading import Thread
from Queue import Queue
def worker():
while True:
item = q.get()
do_work(item)
q.task_done()
def do_work(item):
time.sleep(item)
print item
q = Queue()
for i in range(2):
t = Thread(target=worker)
t.daemon = True
t.start()
source = [2,3,1,4,5]
for item in source:
q.put(item)
q.join()
Because otherwise the worker thread would quit as soon as the first job was processed from the queue. The infinite loop ensures that the worker thread retrieves a new job from the queue when finished.
Update: to summarize the comments to my (admittedly hasty) answer: the worker thread is daemonic (ensured by t.daemon = True
), which means that it will automatically terminate when there are only daemonic threads left in the Python interpreter (a more detailed explanation is given here). It is also worth mentioning that the get
method of the queue on which the worker operates blocks the thread when the queue is empty to let other threads run while the worker is waiting for more jobs to appear in the queue.
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