使用多处理从类内的函数返回值

Question

我有下面的代码，我想在并行处理完成后如何获得返回值。我不喜欢对getdata函数做任何更改。

from multiprocessing import Process

class Calculation(object):
    def __init__(self, a, b, c):
        self.A, self.B, self.C= a, b, c
        
    def getdata(self):
        self.Product = self.A * self.B
        self.Subtract = self.C - self.B
        self.Addition = self.A + self.B + self.C
        return self.Product, self.Subtract, self.Addition
    

def foo():
    EXTERNAL_C=[10, 20, 30, 40, 50, 20, 40]
    c = [Calculation(a=4, b=5, c=n) for n in EXTERNAL_C]
    return c
    
K = []
for M in foo():
    p = Process(target=M.getdata)
    p.start()
    K.append(p)
for process in K:
    process.join()
print(K)

输出：

[<Process(Process-8, stopped[1])>, <Process(Process-9, stopped[1])>, <Process(Process-10, stopped[1])>, <Process(Process-11, stopped[1])>, <Process(Process-12, stopped[1])>, <Process(Process-13, stopped[1])>, <Process(Process-14, stopped[1])>]

Answer 1

您在主进程中创建的Calculation对象被复制到生成的进程中，因此存在没有办法提取他们的状态或获得getdata的返回值，而不进行显式操作。

您可以使用multiprocessing.Queue来存储结果，如下所示

from multiprocessing import Process, Queue


class Calculation(object):
    def __init__(self, a, b, c):
        self.A, self.B, self.C = a, b, c

    def getdata(self, id, queue):
        self.Product = self.A * self.B
        self.Subtract = self.C - self.B
        self.Addition = self.A + self.B + self.C
        queue.put(
            {
                "id": id,
                "Product": self.Product,
                "Subtract": self.Subtract,
                "Addition": self.Addition,
            }
        )


def foo():
    EXTERNAL_C = [10, 20, 30, 40, 50, 20, 40]
    c = [Calculation(a=4, b=5, c=n) for n in EXTERNAL_C]
    return c


K = []
f = foo()
queue = Queue()
for id, M in enumerate(f):
    p = Process(target=M.getdata, args=(id, queue))
    p.start()
    K.append(p)
for process in K:
    process.join()

results = [queue.get() for i in range(len(f))]
print(results)