Python - 多处理错误 'cannot start a process twice'

Question

我尝试使用 Python 中的 multiprocessing 包开发算法，我从互联网上学习了一些教程并尝试使用这个包开发算法。在环顾四周并使用 Process、Queue 和 Pool 尝试我的“hello world”之后，我尝试在此代码上实现 Queue

def main(queue):
   d = ...
   k = ...
   filename, patname, txt, pat = ...
   R = queue
   processes = []

   for j in range(k-1):
        processes.append(Process(target=sim, args=(int(j * d), int((j+1) * d), txt, pat, filename, patname, R, )))

   # processes.append(Process(target=sim, args=(int(j * d), len(txt), txt, pat, filename, patname, R, )))       

   for pr in processes:
        pr.start()

   for pr in processes:
        pr.join()

   while not R.empty():
        print (R.get())

if __name__ == '__main__':
    R = Queue()
    main(R)

但是，出现如下错误:

AssertionError: Cannot start a process twice

谁能帮忙解决这个问题

完整输出:

sim(e_original.txt, e_modify0%.txt) = 0.000000
sim(e_original.txt, e_modify0%.txt) = 0.000000
1
Traceback (most recent call last):
  File "measure.py", line 108, in <module>
    main()
  File "measure.py", line 98, in main
    pr.start()
  File "C:\Python27\lib\multiprocessing\process.py", line 120, in start
    assert self._popen is None, 'cannot start a process twice'
AssertionError: cannot start a process twice
sim(e_original.txt, e_modify0%.txt) = 0.000000

Answer 1

您得到断言是因为您多次对单个 Process 对象调用 start。您的示例在第二个 process.append 中存在缩进错误，我假设该行根本不应该存在。请注意，您启动进程的 for 循环位于上面的 for 循环内，因此它会为您创建的每个进程执行。例如，在第二次循环中，您创建了第二个进程，然后尝试再次启动第一个进程。只需将开始代码移出上面的 for 循环即可。

processes = []

for j in range(k-1):
    processes.append(Process(target=sim, args=(int(j * d), int((j+1) * d), txt, pat, filename, patname, R, )))

for pr in processes:
    pr.start()

for pr in processes:
    pr.join()

while not R.empty():
    print (R.get())