threading.Lock()互斥锁

threading.Lock()是Python中的线程锁，用于在多线程程序中控制线程对共享资源的访问。当一个线程获得了锁之后，其他线程需要等待这个线程释放锁之后才能继续访问共享资源。

下面是threading.Lock()的基本用法示例：

import threading

# 创建一个Lock对象
lock = threading.Lock()

# 在需要保护共享资源的地方使用acquire()方法获取锁
lock.acquire()
try:
    # 访问共享资源
    print("Accessing shared resource")
finally:
    # 使用完共享资源后释放锁
    lock.release()

不用互斥锁的demo ：

import threading
import time

lock = threading.Lock()
a = 1


def func1():
    global a
    while a < 20:
        print(a, end=', ')
        a += 1
        time.sleep(1)


def func2():
    global a
    while a < 20:
        print(a, end=', ')
        a += 1
        time.sleep(1)


def func3():
    global a
    while a < 20:
        print(a, end=', ')
        a += 1
        time.sleep(1)


th1 = threading.Thread(target=func1)
th2 = threading.Thread(target=func2)
th3 = threading.Thread(target=func3)

th1.start()
th2.start()
th3.start()


# 输出结果：1, 2, 3, 44, 4, , 777, , , 1010, , 10, 131313, , , 1616, 16, , 19, 19, 

看得出，由于多线程同时访问同一个变量，变量的变化是随机和混乱的。

使用with方法的demo：

import threading
import time

lock = threading.Lock()
x = 0


def func_a():
    global x
    while True:
        if x < 6:
            with lock:
                x += 1
                print('func_a', x, end=', ')
            time.sleep(0.5)
        else:
            break



def func_b():
    global x
    while True:
        if x < 6:
            with lock:
                x += 1
                print('func_b', x, end=', ')
            time.sleep(0.5)
        else:
            break

# func_b 和 func_c 函数也相应地做相同的修改

def func_c():
    global x
    while True:
        if x < 6:
            with lock:
                x += 1
                print('func_c', x, end=', ')
            time.sleep(0.5)
        else:
            break

# func_b 和 func_c 函数也相应地做相同的修改


th1 = threading.Thread(target=func_a)
th2 = threading.Thread(target=func_b)
th3 = threading.Thread(target=func_c)

th1.start()
th2.start()
th3.start()

# 输出：func_a 1, func_b 2, func_c 3, func_a 4, func_b 5, func_c 6, 

有了互斥锁后，线程对变量的访问是唯一和有序的。

使用lock.acquire()和lock.release()的demo：

import threading
import time

lock = threading.Lock()


def func_a():
    global x
    while True:
        if x < 6:
            lock.acquire()
            try:
                x += 1
                print('func_a', x, end=', ')
            finally:
                lock.release()
                time.sleep(0.5)
        else:
            break


def func_b():
    global x
    while True:
        if x < 6:
            lock.acquire()
            try:
                x += 1
                print('func_b', x, end=', ')
            finally:
                lock.release()
                time.sleep(0.5)
        else:
            break


def func_c():
    global x
    while True:
        if x < 6:
            lock.acquire()
            try:
                x += 1
                print('func_c', x, end=', ')
            finally:
                lock.release()
                time.sleep(0.5)
        else:
            break


th1 = threading.Thread(target=func_a)
th2 = threading.Thread(target=func_b)
th3 = threading.Thread(target=func_c)

th1.start()
th2.start()
th3.start()

# 输出：func_a 1, func_b 2, func_c 3, func_c 4, func_b 5, func_a 6,