如何在數據類中使用 multithreading.Value？

Question

你們中有人知道是否可以在dataclass中使用multiprocessing.Value字段嗎？

對於以下數據類定義，我得到TypeError: this type has no size exception。

import multiprocessing
from dataclasses import dataclass

@dataclass
class TestResults:
    count: multiprocessing.sharedctypes.Synchronized = multiprocessing.Value(int, 0)

堆棧跟蹤：

$ python example.py 
Traceback (most recent call last):
  File "/tmp/example.py", line 5, in <module>
    class TestResults:
  File "/tmp/example.py", line 6, in TestResults
    count: multiprocessing.sharedctypes.Synchronized = multiprocessing.Value(int, 0)
  File "/usr/lib/python3.10/multiprocessing/context.py", line 135, in Value
    return Value(typecode_or_type, *args, lock=lock,
  File "/usr/lib/python3.10/multiprocessing/sharedctypes.py", line 74, in Value
    obj = RawValue(typecode_or_type, *args)
  File "/usr/lib/python3.10/multiprocessing/sharedctypes.py", line 49, in RawValue
    obj = _new_value(type_)
  File "/usr/lib/python3.10/multiprocessing/sharedctypes.py", line 40, in _new_value
    size = ctypes.sizeof(type_)
TypeError: this type has no size

Answer 1

multiprocessing.Value需要第一個參數作為數組類型，因此對於 int，您應該傳入 2 個字節的“i”或 4 個字節整數的“l”。

由於它是可變類型，因此您需要使用field(default_factory)來構造它。

import multiprocessing
from dataclasses import dataclass, field
import multiprocessing.sharedctypes

@dataclass
class TestResults:
    count: multiprocessing.sharedctypes.Synchronized = field(default_factory=lambda: multiprocessing.Value('i', 0))