在python中使用多處理的共享對象數組

Question

我試圖在python程序中的不同進程之間創建一個共享對象（類的實例）的數組。 這些對象中的每一個都將在程序中進行修改。 為此，我使用多處理如下：

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

我得到的錯誤是：

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

現在我的問題是，首先，這通常是解決這個問題的正確方法，其次，我在上面的代碼中的錯誤是什么？ 先感謝您。

Answer 1

ctypes.py_object表示C中的PyObject * 。它是一個指向struct的指針，表示Python對象，駐留在進程的私有內存中，並包含更多指針。 另一個進程無法訪問它; 嘗試在進程之間共享指針是沒有用的。

請參閱Alex Martelli的回答 。

Answer 2

您可能希望使用multiprocessing.Queue ，您可以在其中轉儲對象而無需擔心類型。 它還具有線程安全性和過程安全性。

這是一個簡單的Queue用於促進生產者 - 消費者問題的例子（ 原始來源 ，Pizzas是我的一點獎勵）。

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()

下面是一個示例輸出。 如果運行它，Producer和Consumer打印語句可能會以不同方式交錯，因為並行進程的執行不確定。

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!

請注意，您應該使用Sentinels標記隊列的結尾 。 我在這里使用過“NO PIZZA”，但它們可以是任何東西。