python 多线程 共同写一个变量

https://docs.python.org/3/library/threading.html#threading.Condition

https://stackoverflow.com/questions/17774768/python-creating-a-shared-variable-between-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()