线程的两种创建方式:(重点)
一方式
From threading import Thread
Def f1(n):
Print(n)
main:
T = Thread(target=f1,args=(1,))
T.start()
二方式
Class MyThread(Thread):
Def __init__(self,n):
Super().__init__()
Self.n = n
Def run(self):
Pass
Main:
T = MyThread(5)
T.start()
进程:资源分配单位
线程:cpu执行单位(实体)
多线程和多进程运行时间对比:
import time from threading import Thread from multiprocessing import Process def f1(): a = 100 b = a**2 if __name__ == '__main__': t_time = time.time() t_lis = [] for i in range(10): t = Thread(target=f1,) t.start() t_lis.append(t) [i.join() for i in t_lis] t__time = time.time() t___time = t__time - t_time p_time = time.time() p_lis = [] for i in range(10): p = Process(target=f1, ) p.start() p_lis.append(p) [i.join() for i in p_lis] p__time = time.time() p___time = p__time - p_time print("多线程时间:", t___time) print("多进程时间:", p___time)
锁:牺牲了效率,保证了数据安全(重点)
线程的创建和销毁的开销特别小
线程之间资源共享,共享的是同一个进程中的资源
资源共享就涉及到数据安全问题,加锁来解决
from threading import Thread,Lock
loc = Lock()
t = thread(target=f1,args=(loc,))
锁: ( 或者用with )
loc.acquire()
代码
loc.release()
import time from threading import Thread,Lock num = 10 def f1(n): global num with n : tmg = num tmg -= 1 time.sleep(0.001) num = tmg print(f"子线程执行完的num的值为:{num}") if __name__ == '__main__': loc = Lock() t_lis = [] for i in range(10): t = Thread(target=f1,args=(loc,)) t.start() t_lis.append(t) [i.join() for i in t_lis] print(f"num的值为:{num}")
死锁现象:出现在锁嵌套的时候,双方互相抢对方已经拿到的锁,导致双方互相等待,天长地久永不分离,死锁现象(重点)
def fun1(n,m): n.acquire() print(f">>>1号抢到了A锁") time.sleep(0.5) m.acquire() print(f">>>1号抢到了B锁") m.release() n.release() def fun2(n,m): m.acquire() print(f">>>2号抢到了B锁") time.sleep(0.5) n.acquire() print(f">>>2号抢到了A锁") n.release() m.release() if __name__ == '__main__': locA = Lock() locB = Lock() t1 = Thread(target=fun1,args=(locA,locB,)) t2 = Thread(target=fun2,args=(locA, locB,)) t1.start() t2.start()
递归锁:解决死锁现象(重点)
Rlock 首先本身就是个互斥锁,维护了一个计数器,每次acquire就+1,release就-1,当计数器为0的时候,大家才能抢这个锁
import time from threading import Thread,RLock def fun1(n,m): n.acquire() print(f">>>1号抢到了A锁") time.sleep(0.5) m.acquire() print(f">>>1号抢到了B锁") m.release() n.release() def fun2(n,m): m.acquire() print(f">>>2号抢到了B锁") time.sleep(0.5) n.acquire() print(f">>>2号抢到了A锁") n.release() m.release() if __name__ == '__main__': locA = locB = RLock() t1 = Thread(target=fun1,args=(locA,locB,)) t2 = Thread(target=fun2,args=(locA, locB,)) t1.start() t2.start()
守护线程(小重点)
守护线程:等待所有非守护线程的结束才结束
守护进程:主进程代码运行结束,守护进程就随之结束
GIL锁(重点) : cpython解释器上的一把互斥锁.了解python怎么运行线程
线程的信号量,事件 与 进程的信号量,事件 逻辑一样.(了解内容,见前面进程的博客)