python - 具有局部变量的全局方法线程安全

Question

我有一个 python 项目，我在其中添加一个包含以下内容的新文件 utils.py 。它将被不同的线程访问。

def get_return_string(input_string, input_dict):
    ret_str = 'some default value'
    if 'apple' in input_string:
        ret_str = input_dict['apple']
    elif 'banana' in input_string:
        ret_str = input_dict['banana']
    elif 'grapes' in input_string:
        ret_str = input_dict['grapes']
    elif 'spinach' in input_string:
        ret_str = input_dict['spinach']
    elif 'orange' in input_string:
        ret_str = input_dict['orange']
    elif 'berry' in input_string:
        ret_str = input_dict['berry']
    return ret_str

只有局部变量，它们是从另一个类的内部实例中调用的。这个方法线程安全吗？

我读到here那:

Local variables are certainly "thread-exclusive." No other thread can access them directly, and this is helpful but not sufficient to guarantee semantic thread safety. A local variable in one thread does not store its value in the same location as the same-named local variable in another thread

和

However, guaranteeing that two threads have separate storage for local variables is not enough to ensure thread-safety, because those local variables can refer to globally shared data in a thread-unsafe way.

如果该方法是类方法而不是全局方法，那么它的行为也会有所不同:

class Utils():

    @classmethod
    def get_return_string(cls, input_string, input_dict):
        #...same as above...

Answer 1

是的，该函数是线程安全的，因为局部变量实际上没有访问任何全局变量，您可以通过在方法中打印 ret_str 的值来检查

def get_return_string(input_string, input_dict):
    ret_str = 'some default value'
    if 'apple' in input_string:
        ret_str = input_dict['apple']
    elif 'banana' in input_string:
        ret_str = input_dict['banana']
    elif 'grapes' in input_string:
        ret_str = input_dict['grapes']
    elif 'spinach' in input_string:
        ret_str = input_dict['spinach']
    elif 'orange' in input_string:
        ret_str = input_dict['orange']
    elif 'berry' in input_string:
        ret_str = input_dict['berry']
    print(ret_str)
    return ret_str

from threading import Thread

dct = {'apple':1,'banana':2}
t1 = Thread(target=get_return_string, args=('apple',dct))
t2 = Thread(target=get_return_string, args=('fruit',dct))
t3 = Thread(target=get_return_string, args=('banana',dct))
t1.start()
t2.start()
t3.start()
t1.join()
t2.join()
t3.join()
#1
#some default value
#2