锁机制,信号机制及事件机制

　　在多进程运行处理数据时,会出现争夺资源到时数据混乱的现象,为了避免数据混乱,这里就引入了锁机制:

 锁机制:引入Lock模块,l = Lock()在子进程中,l.acquire()表示取到钥匙,锁上门进行数据处理;l.release()表示归还钥匙打开门,让下一个进程进行操作.

信号机制:能够将一把锁配置多把钥匙,能够让多个进程同时进行操作.导入Semaphore模块,sem = Semaphore(n)中的n是int型,表示可以同时进行操作的子程序数.

事件机制:导入Event模块,e.is_set()初始值是False,e.wait()判断is_set()的布尔值,如果是True就实现非阻塞状态,如果是Flaser则是实现阻塞状态(能顾实现一个子进程控制另一个子进程的执行).e.set()将is_set()设为True,e.clear()将其设为False

下面举几个例子说明:

"""12306抢票的例子(Lock)锁机制"""
from multiprocessing import Process,Lock
import time

def check(i):
    with open("lest")as f:
        conn = int(f.read())
        print("第%s个人查到还剩%s张票" % (i,conn))

def buy_(i,l):
    l.acquire()
    with open("lest")as f:
        conn = int(f.read())
        if conn > 0:
            print("第%s个人买到了票" % i)
            conn -= 1
        else:
            print("第%s个人没有买到票" % i)
    time.sleep(0.5)
    with open("lest","w")as f1:
        f1.write(str(conn))
        f1.close()
    l.release()

if __name__ == '__main__':
    l = Lock()
    for i in range(5):
        p = Process(target=check,args=(i+1,))
        p.start()
        p1 = Process(target=buy_,args=(i+1,l))
        p1.start()

"""红绿灯的例子(事件机制)"""
from multiprocessing import Process,Event
import time

def light(e):
    while 1:
        if e.is_set():
            time.sleep(3)
            print("红灯亮")
            e.clear()
        else:
            time.sleep(3)
            print("绿灯亮")
            e.set()

def car(i,e):
    e.wait()
    print("第%s辆车通过" % i)


if __name__ == '__main__':
    e = Event()
    light_ = Process(target=light,args=(e,))
    light_.start()
    for i in range(20):
        time.sleep(0.5)
        car_ = Process(target=car,args=(i+1,e))
        car_.start()

"""小黑屋例子(Semaphore(n)信号机制)"""
from multiprocessing import Process,Semaphore
import time

def func(i,sem):
    sem.acquire()
    print("第%s个人来了" % i)
    time.sleep(3)
    print("第%s个人又走了" % i)
    sem.release()

if __name__ == '__main__':
    sem = Semaphore(3)
    for i in range(10):
        p = Process(target=func,args=(i+1,sem))
        p.start()

"""存钱取钱的例子(Lock,Value)"""
from multiprocessing import Process,Lock,Value

def get(num,l,s):
    l.acquire()
    num.value -= int(s)
    l.release()

def put(num,l,s1):
    l.acquire()
    num.value += int(s1)
    l.release()


if __name__ == '__main__':
    num = Value("i",100)
    s = input("取钱:")
    s1 = input("存钱:")
    l = Lock()
    p = Process(target=get,args=(num,l,int(s)))
    p.start()
    p.join()
    p1 = Process(target=put,args=(num,l,int(s1)))
    p1.start()
    p1.join()
    print(num.value)