Question

为什么这段代码“行为”没有线程？（请参阅输出。）

import time
from threading import Thread

def main():
    for nums in [range(0,5), range(5,10)]:
        t = Spider(nums)
        t.start()
        print 'started a thread'
        t.join()
    print "done"

class Spider(Thread):
    def __init__(self, nums):
        Thread.__init__(self)
        self.nums = nums
    def run(self):  # this is an override
        for num in self.nums:
            time.sleep(3)  # or do something that takes a while
            print 'finished %s' % (num, )

if __name__ == '__main__':
    main()

输出：

started a thread
finished 0
finished 1
finished 2
finished 3
finished 4
started a thread
finished 5
finished 6
finished 7
finished 8
finished 9
done

Answer 1

当你说t.join()时，你告诉它等待线程结束。

这意味着，你要求它创建一个线程，启动它，然后在创建新线程之前等待线程结束。

如果您希望它采用多线程，您需要将join()移到循环之外。

def main():
    # We will store the running threads in this
    threads = []
    # Start the threads
    for nums in [range(0,5), range(5,10)]:
        t = Spider(nums)
        t.start()
        print 'started a thread'
        threads.append(t)
    # All the threads have been started
    # Now we wait for them to finish
    for t in threads:
        t.join()
    print "done"

另见：

Documentation of Thread.join()

Answer 2

您的线程连接t.join阻塞主线程，直到线程完成执行（http://docs.python.org/library/threading.html#threading.Thread.join）。将代码更改为如下所示：

def main():
  threads = [] 
  for nums in [range(0,5), range(5,10)]:
    t = Spider(nums)
    t.start()
    print 'started a thread'
    threads.append(t)
  for t in threads: t.join()
  print "done"

Answer 3

您需要首先启动两个线程，然后在它们都运行时与它们一起加入。

Python线程代码不代表线程化

3 个答案: