python - 从导入的模块线程初始化类变量在 Python 中是安全的吗？

Question

我知道类变量初始化发生在导入时。如果是这样，在下面的代码中，类 A 的类变量初始化是否会导致竞争条件？

a.py:

class A:
    # Static code here...
    pass

b.py:

class B:
    def func(self):
        from a import A

c.py:

import threading
from b import B

b1 = B()
b2 = B()

t1 = threading.Thread(target=b1.func)
t2 = threading.Thread(target=b2.func)

t1.start()
t2.start()

t1.join()
t2.join()

航站楼:

$ python c.py

Answer 1

在 importlib 的 CPython 实现中，C 端有一个线程锁，但为了确定，我运行了以下脚本:

导入文件:

import time
print('importing, in imported file')
time.sleep(2) # drop the GIL
print('finished importing, in imported file')

导入文件:

import threading

def import_other_file():
    print('going to import')
    import ex12
    print('finished importing')

t1 = threading.Thread(target=import_other_file)
t2 = threading.Thread(target=import_other_file)

t1.start()
t2.start()

t1.join()
t2.join()

输出:

going to import
going to import
importing, in imported file
finished importing, in imported file
finished importing
finished importing

does the class variable initialization of class A result in race conditions?

所以NO，不会因为C端的锁而出现竞争条件。