在下面的示例代码中,我想获取函数worker的返回值。我该怎么做呢?这个值存储在哪里?
示例代码:
import multiprocessing
def worker(procnum):
'''worker function'''
print str(procnum) + ' represent!'
return procnum
if __name__ == '__main__':
jobs = []
for i in range(5):
p = multiprocessing.Process(target=worker, args=(i,))
jobs.append(p)
p.start()
for proc in jobs:
proc.join()
print jobs
输出:
0 represent!
1 represent!
2 represent!
3 represent!
4 represent!
[<Process(Process-1, stopped)>, <Process(Process-2, stopped)>, <Process(Process-3, stopped)>, <Process(Process-4, stopped)>, <Process(Process-5, stopped)>]
我似乎无法在存储在作业中的对象中找到相关属性。
我认为@sega_sai建议的方法更好。但它确实需要一个代码示例,所以如下:
import multiprocessing
from os import getpid
def worker(procnum):
print('I am number %d in process %d' % (procnum, getpid()))
return getpid()
if __name__ == '__main__':
pool = multiprocessing.Pool(processes = 3)
print(pool.map(worker, range(5)))
它将打印返回值:
I am number 0 in process 19139
I am number 1 in process 19138
I am number 2 in process 19140
I am number 3 in process 19139
I am number 4 in process 19140
[19139, 19138, 19140, 19139, 19140]
如果你熟悉map (Python 2内置的),这应该不是太有挑战性。否则,请查看sega_Sai的链接。
注意,只需要很少的代码。(还要注意如何重用流程)。
这个例子展示了如何使用multiprocessing的列表。管道实例从任意数量的进程中返回字符串:
import multiprocessing
def worker(procnum, send_end):
'''worker function'''
result = str(procnum) + ' represent!'
print result
send_end.send(result)
def main():
jobs = []
pipe_list = []
for i in range(5):
recv_end, send_end = multiprocessing.Pipe(False)
p = multiprocessing.Process(target=worker, args=(i, send_end))
jobs.append(p)
pipe_list.append(recv_end)
p.start()
for proc in jobs:
proc.join()
result_list = [x.recv() for x in pipe_list]
print result_list
if __name__ == '__main__':
main()
输出:
0 represent!
1 represent!
2 represent!
3 represent!
4 represent!
['0 represent!', '1 represent!', '2 represent!', '3 represent!', '4 represent!']
这种解决方案使用的资源比多进程少。使用
一个管道
至少一个锁
一个缓冲区
一个线程
或者多处理。SimpleQueue使用
一个管道
至少一个锁
查看这些类型的源代码是非常有指导意义的。
一个简单的解决方案:
import multiprocessing
output=[]
data = range(0,10)
def f(x):
return x**2
def handler():
p = multiprocessing.Pool(64)
r=p.map(f, data)
return r
if __name__ == '__main__':
output.append(handler())
print(output[0])
输出:
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]