python - 如何修改正在运行的线程的工作线程中的局部变量？

Question

我想修改正在运行的线程的 target worker 的局部变量:

import threading
import time

def worker():
    a = 1
    while True:
        print(a)
        time.sleep(1)

t = threading.Thread(target=worker)
t.start()
time.sleep(5)
# here I would like to modify a in thread t and set it to 2
t.join()
#
# the expected output would be approximately
# 1
# 1
# 1
# 1
# 1
# 2
# 2
# ...

如何在线程 t 中访问(和修改)a？

Answer 1

简而言之“你不能”。但是，您可以重新设计代码以允许这种情况发生。虽然我会发出警告，但这里有龙。

为了能够修改 a，它需要可访问，最好的方法是让一个对象与包含您要修改的变量的线程相关联。

import threading
import time

# Use a thread class to hold any extra variables we want.
class WorkerThread(threading.Thread):
    def __init__(self, a, **kwargs):
        super().__init__(**kwargs)

        # Store the value of a
        self._a = a

        # Create a lock so thread access is synchronised
        self.lock = threading.Lock()

    # Use a property to control access to a via our lock
    @property
    def a(self):
        with self.lock:
            return self._a

    @a.setter
    def a(self, value):
        with self.lock:
            self._a = value

    # Your origional worker method
    def run(self):
        while True:
            print(self.a)
            time.sleep(1)

# The thread can now be instantiated 
t = WorkerThread(1)
t.start()
time.sleep(5)
# And your value modified.
t.a = 2
time.sleep(5)
t.join()

请注意，尽管使用 join 不会停止线程，它只是等待它完成。