Python Concurrent.期货处理器执行器输出错误

Question

我试图使用ProcessPoolExecutor()来运行一些函数，但我无法理解如何获得函数的返回。

def threaded_upload(i):
time.sleep(2)
if i == 0:
k = 10
elif i == 2:
k = i*i
else:
k = -99
return [k]
def controller():
if __name__ == "__main__":
futures = []
with ProcessPoolExecutor() as pool:
for paso in range(4):
futuro_i = pool.submit(threaded_upload,paso)
wth=[futuro_i.result()]
futures.append(futuro_i)
wait(futures, return_when=ALL_COMPLETED)
merged_list = []
for future in futures:
for valor in future.result():
merged_list.append(valor)
Lista_Final = merged_list
wait(futures, return_when=ALL_COMPLETED)
return Lista_Final
print(controller())

代码的输出是:没有一个[10， -99, 4， -99]

我不知道为什么?"wait"似乎也没有等到所有的函数都执行完。

说实话，我已经阅读和阅读了几天但并行的描述。期货或多处理比我目前的知识更先进。

如能澄清，将不胜感激。提前谢谢。

Answer 1

首先提交作业，然后等待结果。您也可以返回一个整数而不是一个list，然后跳过内部的loop:

test.py:

import random
import time
from concurrent.futures import ProcessPoolExecutor, wait

def worker(i):
t = random.uniform(1, 5)
print(f"START: {i} ({t:.3f}s)")
time.sleep(t)
if i == 0:
k = 10
elif i == 2:
k = i * i
else:
k = -99
print(f"END: {i}")
return k

def main():
futures = []
with ProcessPoolExecutor() as pool:
for i in range(4):
future = pool.submit(worker, i)
futures.append(future)
results = []
done, pending = wait(futures) # ALL_COMPLETED is the default value
for future in done:
results.append(future.result())
print(results)

if __name__ == "__main__":
main()

测试:

$ python test.py
START: 0 (1.608s)
START: 1 (1.718s)
START: 2 (1.545s)
START: 3 (1.588s)
END: 2
END: 3
END: 0
END: 1
[10, -99, 4, -99]