8 解决多线程对共享数据出错

from threading import Thread
import time

g_num = 0
g_flag = 1

def test1():
    global g_num
    global g_flag

    if g_flag == 1:
        for i in range(1000000):
            g_num += 1
        g_flag = 0

    print("---test1---g_num=%d"%g_num)


def test2():
    global g_num
    global g_flag 
    if g_flag != 1:           #test2判断不成功，直接执行print语句，如何让它一直判断下去
        for i in range(1000000): 
            g_num += 1

    print("---test2---g_num=%d"%g_num)


p1 = Thread(target=test1)
p1.start()


p2 = Thread(target=test2)
p2.start()

print("---g_num=%d---"%g_num)

from threading import Thread
import time

g_num = 0
g_flag = 1

def test1():
    global g_num
    global g_flag
    if g_flag == 1:
        for i in range(1000000):
            g_num += 1
        g_flag = 0

    print("---test1---g_num=%d"%g_num)

def test2():
    global g_num
    global g_flag
    #轮询
    while True:
        if g_flag != 1:
            for i in range(1000000):
                g_num += 1
            break

    print("---test2---g_num=%d"%g_num)


p1 = Thread(target=test1)
p1.start()

#time.sleep(3) #取消屏蔽之后 再次运行程序，结果会不一样，，，为啥呢？

p2 = Thread(target=test2)
p2.start()

print("---g_num=%d---"%g_num)

#创建锁
mutex = threading.Lock()
#锁定
mutex.acquire([blocking])
#释放
mutex.release()

from threading import Thread, Lock
import time

g_num = 0

def test1():
    global g_num
    #这个线程和ｔｅｓｔ2线程都在抢着　对这个锁　进行上锁，如果有１方成功的上锁，那么导致另外
    #一方会堵塞（一直等待）到这个锁被解开为止
    mutex.acquire()
    for i in range(1000000):
        g_num += 1
    mutex.release()#用来对mutex指向的这个锁　进行解锁，，，只要开了锁，那么接下来会让所有因为
                    #这个锁　被上了锁　而堵塞的线程　进行抢着上锁

    print("---test1---g_num=%d"%g_num)

def test2():
    global g_num
    mutex.acquire()
    for i in range(1000000):
        g_num += 1
    mutex.release()

    print("---test2---g_num=%d"%g_num)

#创建一把互斥锁，这个锁默认是没有上锁的
mutex = Lock()

p1 = Thread(target=test1)
p1.start()

#time.sleep(3) #取消屏蔽之后 再次运行程序，结果会不一样，，，为啥呢？

p2 = Thread(target=test2)
p2.start()

print("---g_num=%d---"%g_num)

from threading import Thread, Lock
import time

g_num = 0

def test1():
    global g_num
    for i in range(1000000):
        mutex.acquire()
        g_num += 1
        mutex.release()

    print("---test1---g_num=%d"%g_num)

def test2():
    global g_num
    for i in range(1000000):
        mutex.acquire()
        g_num += 1
        mutex.release()

    print("---test2---g_num=%d"%g_num)

mutex = Lock()

p1 = Thread(target=test1)
p1.start()

p2 = Thread(target=test2)
p2.start()

print("---g_num=%d---"%g_num)

1.每次上锁两个线程都要抢
2.每次第一个线程释放锁，两个程序都要继续抢上锁