Question

我想修改正在运行的线程的target工作者的局部变量：

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a中访问（和修改）t？

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。尽管我会发出警告，但这里还是龙。

要能够修改a，它必须是可访问的，最好的方法是让一个与线程相关联的对象保存您要修改的变量。

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，但只是等待线程完成。

Answer 2

您不能修改线程的局部变量。而是使用全局变量执行此任务：

import threading
import time

a = 1

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

t = threading.Thread(target=worker)
t.start()
time.sleep(5)
a = 2
t.join()

如何在正在运行的线程的工作程序中修改局部变量？

2 个答案: