Python在线程之间创建共享变量

问题描述

我正在使用线程"模块在Python中进行项目开发.

I'm working on a project in Python using the "thread" module.

如何创建一个全局变量(在我的情况下，我需要为True或False)，以便项目中的所有线程(大约4-6)都可以访问?

How can I make a global variable (in my case I need it to be True or False) that all the threads in my project (about 4-6) can access?

推荐答案

我们可以在线程类外部定义变量，并在类的方法内部将其全局声明.

We can define the variable outside the thread classes and declare it global inside the methods of the classes.

请参见下面的简单示例，该示例交替打印AB.两个线程Thread_A和Thread_B之间共享两个变量flag和val. Thread_A打印val=20，然后将val设置为30.Thread_B打印val=30，因为在Thread_A中修改了val. Thread_B然后将val设置为20，再次在Thread_A中使用.这说明了变量val在两个线程之间共享.同样，两个线程之间也共享变量flag.

Please see below trivial example which prints AB alternatively. Two variables flag and val are shared between two threads Thread_A and Thread_B. Thread_A prints val=20 and then sets val to 30. Thread_B prints val=30, since val is modified in Thread_A. Thread_B then sets val to 20 which is again used in Thread_A. This demonstrates that variable val is shared between two threads. Similarly variable flag is also shared between two threads.

import threading
import time
c = threading.Condition()
flag = 0      #shared between Thread_A and Thread_B
val = 20

class Thread_A(threading.Thread):
    def __init__(self, name):
        threading.Thread.__init__(self)
        self.name = name

    def run(self):
        global flag
        global val     #made global here
        while True:
            c.acquire()
            if flag == 0:
                print "A: val=" + str(val)
                time.sleep(0.1)
                flag = 1
                val = 30
                c.notify_all()
            else:
                c.wait()
            c.release()


class Thread_B(threading.Thread):
    def __init__(self, name):
        threading.Thread.__init__(self)
        self.name = name

    def run(self):
        global flag
        global val    #made global here
        while True:
            c.acquire()
            if flag == 1:
                print "B: val=" + str(val)
                time.sleep(0.5)
                flag = 0
                val = 20
                c.notify_all()
            else:
                c.wait()
            c.release()


a = Thread_A("myThread_name_A")
b = Thread_B("myThread_name_B")

b.start()
a.start()

a.join()
b.join()

输出看起来像

A: val=20
B: val=30
A: val=20
B: val=30
A: val=20
B: val=30
A: val=20
B: val=30

每个线程都会打印在另一个线程中修改的值.

Each thread prints the value which was modified in another thread.

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