Question

我正在尝试在python程序中的不同进程之间创建一个共享对象数组（类的实例）。这些对象中的每一个都将在程序中进行修改。为此我使用多处理如下：

import multiprocessing
import numpy as np
sh = multiprocessing.RawArray (ctypes.py_object, 10)
f = np.frombuffer(sh, dtype=object)

我得到的错误是：

Traceback (most recent call last):
  File "<pyshell#14>", line 1, in <module>
    f = np.frombuffer(sh, dtype=object)
ValueError: cannot create an OBJECT array from memory buffer

现在我的问题是，首先，这通常是解决这个问题的正确方法，其次，我在上述代码中的错误是什么？提前谢谢。

Answer 1

ctypes.py_object表示C中的PyObject *。它是指向struct的指针，表示Python对象，驻留在进程的私有内存中，并包含更多指针。另一个进程无法访问它;尝试在进程之间共享指针是没有用的。

另见this answer by Alex Martelli。

Answer 2

您可能希望使用multiprocessing.Queue，您可以在其中转储对象而无需担心类型。它还具有线程安全性和过程安全性。

这是一个简单的Queue用于促进制片人 - 消费者问题的例子（original source，Pizzas是我的一点奖励。）

from multiprocessing import Process, Queue

class Pizza(object):
    def __init__(self, pizza_num):
        self.pizza_num = pizza_num
        self.num_slices = 8

sentinel = "NO PIZZA"

def producer(initial_num_pizzas, total_num_pizzas, q):
    """Cooks Pizzas to be consumed and waits for the consumer to finish eating."""
    print("Producer: I am cooking %s Pizzas and putting them on the Queue!"%(total_num_pizzas-initial_num_pizzas))
    for i in range(q.qsize(), total_num_pizzas):
        print("Producer: Behold, for I have cooked Pizza no. %s"%i)
        q.put(Pizza(i))
    q.put(sentinel)

def consumer(q):
    """Consumes some Pizza. In this case, all it does is set the number of slices to 0."""
    while True:
        pizza = q.get()
        pizza.num_slices = 0
        if pizza == sentinel:
            break
        print("Comsumer: Pizza no. %s was found! It has %s slices, yum!"%(pizza.pizza_num, pizza.num_slices))

if __name__ == '__main__':
    q = Queue()
    total_num_pizzas = 10
    initial_num_pizzas = 4
    ## Let's add some Pizzas beforehand:
    for i in range(0, initial_num_pizzas):
        q.put(Pizza(i))
    print("Main: I have precooked %s Pizzas."%q.qsize())

    producer_proc = Process(target=producer, args=(initial_num_pizzas, total_num_pizzas, q))
    consumer_proc = Process(target=consumer, args=(q,))
    producer_proc.start()
    consumer_proc.start()

    q.close()  ## Shop is closed, no more Pizzas will be added to Queue!
    q.join_thread()

    producer_proc.join()
    consumer_proc.join()

以下是输出示例。如果运行它，Producer和Consumer打印语句可能会以不同方式交错，因为并行进程的执行不确定。

Main: I have precooked 4 Pizzas.
Producer: I am cooking 6 Pizzas and putting them on the Queue!
Producer: Behold, for I have cooked Pizza no. 4
Producer: Behold, for I have cooked Pizza no. 5
Producer: Behold, for I have cooked Pizza no. 6
Producer: Behold, for I have cooked Pizza no. 7
Comsumer: Pizza no. 0 was found! It has 8 slices, yum!
Comsumer: Pizza no. 1 was found! It has 8 slices, yum!
Producer: Behold, for I have cooked Pizza no. 8
Comsumer: Pizza no. 2 was found! It has 8 slices, yum!
Producer: Behold, for I have cooked Pizza no. 9
Comsumer: Pizza no. 3 was found! It has 8 slices, yum!
Comsumer: Pizza no. 4 was found! It has 8 slices, yum!
Comsumer: Pizza no. 5 was found! It has 8 slices, yum!
Comsumer: Pizza no. 6 was found! It has 8 slices, yum!
Comsumer: Pizza no. 7 was found! It has 8 slices, yum!
Comsumer: Pizza no. 8 was found! It has 8 slices, yum!
Comsumer: Pizza no. 9 was found! It has 8 slices, yum!

请注意，您应该use Sentinels to mark the end of your Queue。我已经使用了＃34; NO PIZZA＆＃34;在这里，但它们可以是任何东西。

在python中使用多处理的共享对象数组

2 个答案: