锁、信号量和资源互斥分别指什么？请用python程序举例说明。

# ### 信号量 Semaphore
from threading import Semaphore, Thread
import time


def func(i, sem):
    with sem:
        print(i)
        time.sleep(10)


sem = Semaphore(6)
for i in range(20):
    Thread(target=func, args=(i, sem)).start()

# 枷锁
import time, threading
count=0 #声明全局变量
lock=threading.Lock() #申请一把锁
def lajifenlei():
    global count #引用全局变量
    lock.acquire()  #加锁
    count+=1
    lock.release() #释放锁
    time.sleep(1)
    print(count)

for i in range(10):
    th = threading.Thread(target=lajifenlei,) #声明线程数
    th.start() #启动线程
while threading.activeCount()!=1:
    pass