python之線程鎖

junnplus 發(fā)布于2019-07-30 18:38 / 2430人閱讀

摘要：信號(hào)量使用前執(zhí)行后發(fā)現(xiàn)不斷在輸出使用后通過執(zhí)行上面的代碼，我們發(fā)現(xiàn)一次只能輸出三個(gè)數(shù)字，控制訪問并發(fā)量事件等待后，才能往下執(zhí)行定義五個(gè)線程重置，使得起到阻塞作用啟動(dòng)所有線程等待喚醒所有線程等待喚醒所有線程

本文講python中的四種鎖
Lock互斥鎖
使用前

num = 0


def a():
    global num
    for _ in range(10000000):
        num += 1


def b():
    global num
    for _ in range(10000000):
        num += 1


if __name__ == "__main__":
    t1=Thread(target=a)
    t1.start()
    t2=Thread(target=b)
    t2.start()
    t1.join()
    t2.join()
    print(num)    #基本永遠(yuǎn)會(huì)小于20000000

使用后

num = 0


def a(lock):
    global num
    for _ in range(1000000):
        with lock:
            num += 1


def b(lock):
    global num
    for _ in range(1000000):
        with lock:
            num += 1


if __name__ == "__main__":
    lock = threading.Lock()
    t1=Thread(target=a, args=(lock,))
    t1.start()
    t2=Thread(target=b, args=(lock,))
    t2.start()
    t1.join()
    t2.join()
    print(num)    #永遠(yuǎn)會(huì)輸出20000000

RLock重用鎖

#在之前的代碼中永遠(yuǎn)不可能出現(xiàn)鎖在沒釋放之前重新獲得鎖，但rlock可以做到，但只能發(fā)生在一個(gè)線程中，如：
num = 0


def a(lock):
    with lock:
        print("我是A")
        b(lock)


def b(lock):
    with lock:
        print("我是b")

if __name__ == "__main__":
    lock = threading.Lock()
    t1 = Thread(target=a, args=(lock,))
    t1.start()    #會(huì)發(fā)生死鎖，因?yàn)樵诘谝淮芜€沒釋放鎖后，b就準(zhǔn)備上鎖，并阻止a釋放鎖

使用后

if __name__ == "__main__":
    lock = threading.RLock()    #只需要改變鎖為RLock程序馬上恢復(fù)
    t1 = Thread(target=a, args=(lock,))
    t1.start()

Condition同步鎖

#這個(gè)程序我們模擬甲乙對(duì)話
Jlist = ["在嗎", "干啥呢", "去玩兒不", "好吧"]
Ylist = ["在呀", "玩兒手機(jī)", "不去"]


def J(list):
    for i in list:
        print(i)
        time.sleep(0.1)


def Y(list):
    for i in list:
        print(i)
        time.sleep(0.1)


if __name__ == "__main__":
    t1 = Thread(target=J, args=(Jlist,))
    t1.start()
    t1.join()
    t2 = Thread(target=Y, args=(Ylist,))
    t2.start()
    t2.join()    #上面的程序輸出后發(fā)現(xiàn)效果就是咱們想要的，但是我們每次輸出后都要等待0.1秒，也無法正好確定可以拿到時(shí)間片的最短時(shí)間值，并且不能保證每次正好都是另一個(gè)線程執(zhí)行。因此，我們用以下方式，完美解決這些問題。

使用后

Jlist = ["在嗎", "干啥呢", "去玩兒不", "好吧"]
Ylist = ["在呀", "玩兒手機(jī)", "不去","哦"]


def J(cond, list):
    for i in list:
        with cond:
            print(i)
            cond.notify()
            cond.wait()


def Y(cond, list):
    for i in list:
        with cond:
            cond.wait()
            print(i)
            cond.notify()


if __name__ == "__main__":
    cond = threading.Condition()
    t1 = Thread(target=J, args=(cond, Jlist))
    t2 = Thread(target=Y, args=(cond, Ylist))
    t2.start()
    t1.start()    #一定保證t1啟動(dòng)在t2之后,因?yàn)閚otify發(fā)送的信號(hào)要被t2接受到，如果t1先啟動(dòng)，會(huì)發(fā)生阻塞。

Seamplore信號(hào)量
使用前

class B(threading.Thread):
    def __init__(self, name):
        super().__init__()
        self.name = name

    def run(self):
        time.sleep(1)
        print(self.name)


class A(threading.Thread):
    def __init__(self):
        super().__init__()

    def run(self):
        for i in range(100):
            b = B(i)
            b.start()


if __name__ == "__main__":
    a = A()
    a.start()    #執(zhí)行后發(fā)現(xiàn)不斷在輸出

使用后

class B(threading.Thread):
    def __init__(self, name, sem):
        super().__init__()
        self.name = name
        self.sem = sem

    def run(self):
        time.sleep(1)
        print(self.name)
        sem.release()


class A(threading.Thread):
    def __init__(self, sem):
        super().__init__()
        self.sem = sem

    def run(self):
        for i in range(100):
            self.sem.acquire()
            b = B(i, self.sem)
            b.start()


if __name__ == "__main__":
    sem = threading.Semaphore(value=3)
    a = A(sem)
    a.start()    #通過執(zhí)行上面的代碼，我們發(fā)現(xiàn)一次只能輸出三個(gè)數(shù)字，sem控制訪問并發(fā)量

Event事件

import time
import threading


class MyThread(threading.Thread):
    def __init__(self, name, event):
        super().__init__()
        self.name = name
        self.event = event

    def run(self):
        print("Thread: {} start at {}".format(self.name, time.ctime(time.time())))
        # 等待event.set()后，才能往下執(zhí)行
        self.event.wait()
        print("Thread: {} finish at {}".format(self.name, time.ctime(time.time())))


event = threading.Event()

# 定義五個(gè)線程
threads = [MyThread(str(i), event) for i in range(1,5)]

# 重置event，使得event.wait()起到阻塞作用
event.clear()

# 啟動(dòng)所有線程
[t.start() for t in threads]

print("等待5s...")
time.sleep(5)

print("喚醒所有線程...")
event.set()

# output:
"""
Thread: 1 start at Sun May 13 20:38:08 2018
Thread: 2 start at Sun May 13 20:38:08 2018
Thread: 3 start at Sun May 13 20:38:08 2018
Thread: 4 start at Sun May 13 20:38:08 2018

等待5s...

喚醒所有線程...
Thread: 1 finish at Sun May 13 20:38:13 2018
Thread: 4 finish at Sun May 13 20:38:13 2018
Thread: 2 finish at Sun May 13 20:38:13 2018
Thread: 3 finish at Sun May 13 20:38:13 2018
"""