python高级-线程和进程相关（下）-阿里云开发者社区

python高级-线程和进程相关（下）

2023-11-17 49

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简介： python高级-线程和进程相关（上）

5.2.方式2

import multiprocessing
import time
g_list = list()
def add_data():
    for i in range(6):
        g_list.append(i)
        print("add: ",i)
        time.sleep(0.2)
    print("add_data: ",g_list)
def read_data():
    print("read_data",g_list)
if __name__ == '__main__':
    # 创建添加数据的子进程
    add_data_process = multiprocessing.Process(target=add_data)
    # 创建读取数据的子进程
    read_data_process = multiprocessing.Process(target=read_data)
    #锁
    add_data_process.daemon = True
    #启动子进程执行对应的任务
    add_data_process.start()
    #阻塞函数，add_data_process执行完才会继续向下执行
    add_data_process.join()
    #全局变量不共享
    read_data_process.start()

五、线程

1.线程创建

import threading
import time
def task1():
    t = threading.currentThread()
    print("task1: ",t)
    for i in range(5):
        print(" Task A ", i+1)
        time.sleep(0.5)
def task2():
    t = threading.currentThread()
    print("task2: ",t)
    for i in range(5):
        print(" Task B ", i+1)
        time.sleep(0.5)
#创建线程
if __name__ == '__main__':
    t1 = threading.Thread(target=task1,name='t1')
    t2 = threading.Thread(target=task2,name='t2')
    print(t1)
    print(t2)
    #创建好线程后，线程并不会被执行
    #必须启动线程
    t1.start()
    t2.start()
    print(t1)
    print(t2)
    print("Main Thread")

2.线程执行带有参数的任务

import threading
import time
def task(count):
    for i in range(count):
        print("任务执行中。。。")
        time.sleep(0.2)
    else:
        print("任务执行完成")
def task1(content , count):
    for i in range(count):
        print(content,'--',i+1)
        time.sleep(0.5)
if __name__ == '__main__':
    sub_thread = threading.Thread(target=task,args=(5,))
    sub_thread2 = threading.Thread(target=task1,args=('Python',5))
    sub_thread.start()
    sub_thread2.start()

3.线程的无序性

import threading
import time
def task():
    t = threading.current_thread()
    for i in range(10):
        print(t.name)
        time.sleep(0.5)
if __name__ == '__main__':
    for i in range(5):
        t = threading.Thread(target=task)
        t.start()

4.守护主线程

没有守护线程，主线程会随即执行

import threading
import time
def task():
    t = threading.current_thread()
    for i in range(5):
        print(t.name)
        time.sleep(0.5)
if __name__ == '__main__':
    t1 = threading.Thread(target=task,name='t1')
    t2 = threading.Thread(target=task,name='t2')
    t1.start()
    t2.start()
    print("main over")

方法1

这个方法主线程不等待子线程所以会出现问题

import threading
import time
def task():
    t = threading.current_thread()
    for i in range(5):
        print(t.name)
        time.sleep(0.5)
if __name__ == '__main__':
    t1 = threading.Thread(target=task,name='t1',daemon=True)
    t2 = threading.Thread(target=task,name='t2',daemon=True)
    t1.start()
    t2.start()
    print("main over")

方法2

import threading
import time
def task():
    t = threading.current_thread()
    for i in range(5):
        print(t.name)
        time.sleep(0.5)
if __name__ == '__main__':
    t1 = threading.Thread(target=task,name='t1')
    t2 = threading.Thread(target=task,name='t2')
    t1.setDaemon(True)
    t2.setDaemon(True)
    t1.start()
    t2.start()
    print("main over")

5.阻塞线程

import threading
import time
def task():
    t = threading.current_thread()
    for i in range(5):
        print(t.name)
        time.sleep(0.5)
if __name__ == '__main__':
    t1 = threading.Thread(target=task,name='t1')
    t2 = threading.Thread(target=task,name='t2')
    t1.setDaemon(True)
    t2.setDaemon(True)
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print("main over")

6.线程间共享全局变量

import threading
import time
c_list = []
def add_data():
    for i in range(5):
        c_list.append(i)
        print(c_list)
        time.sleep(0.5)
def read_data():
    print("read: ",c_list)
if __name__ == '__main__':
    add_t = threading.Thread(target=add_data)
    read_t = threading.Thread(target=read_data)
    add_t.start()
    read_t.start()

7.多线程中共享变量的资源竞争问题

import threading
import time
g_num = 0
def sum_num1():
    for i in range(1000000000):
        global g_num
        g_num += 1
    print("sum1:  ",g_num)
if __name__ == '__main__':
    f_t = threading.Thread(target=sum_num1)
    f_t2 = threading.Thread(target=sum_num1)
    f_t.start()
    f_t2.start()
    time.sleep(3)
    print("main",g_num)

转存失败重新上传取消

时间片轮转的问题

8.使用线程同步解决

线程等待（阻塞）

import threading
import time
g_num = 0
def sum_num1():
    for i in range(1000000000):
        global g_num
        g_num += 1
    print("sum1:  ",g_num)
if __name__ == '__main__':
    f_t = threading.Thread(target=sum_num1)
    f_t2 = threading.Thread(target=sum_num1)
    f_t.start()
    #阻塞
    f_t.join()
    f_t2.start()
    f_t2.join()
    time.sleep(3)
    print("main",g_num)

转存失败重新上传取消

9.互斥锁

上锁

原子操作

解锁

import threading
import time
#创建一个实例锁
metax_lock = threading.Lock()
g_num = 0
def sum_num1():
    t = threading.current_thread()
    for i in range(1000000000):
        metax_lock.acquire()
        global g_num
        g_num += 1
        print(t.name,"=------=",g_num)
        metax_lock.release()
    print("sum1:  ",g_num)
if __name__ == '__main__':
    f_t = threading.Thread(target=sum_num1)
    f_t2 = threading.Thread(target=sum_num1)
    f_t.start()
    f_t2.start()
    time.sleep(3)
    print("main",g_num)

注意不要变成同步锁，一般都是异步执行

10.死锁

这个函数就有个死锁

import multiprocessing
import threading
import time
c_list = [1,2,3,4325]
lock = threading.Lock()
def get_value(index):
    #锁
    lock.acquire()
    t = threading.current_thread()
    if index >= len(c_list):
        print(f'{index} 下界太大，导致下标越界')
        return 
    print(t.name,"取得第",index,'个值，值为',c_list[index])
    lock.release()
if __name__ == '__main__':
    for i in range(5):
        t = threading.Thread(target=get_value,args=(i,))
        t.start()

我们解决掉他

import multiprocessing
import threading
import time
c_list = [1,2,3,4325]
lock = threading.Lock()
def get_value(index):
    #锁
    lock.acquire()
    t = threading.current_thread()
    if index >= len(c_list):
        print(f'{index} 下界太大，导致下标越界')
        lock.release()
        return
    print(t.name,"取得第",index,'个值，值为',c_list[index])
    lock.release()
if __name__ == '__main__':
    for i in range(5):
        t = threading.Thread(target=get_value,args=(i,))
        t.start()

但这里其实还有问题，我们后面讨论

11.死锁哲学家问题

import multiprocessing
import threading
import time
lock_a = threading.Lock()
lock_b = threading.Lock()
def PersonA():
    for i in range(100):
        lock_a.acquire()
        print("A抢到第一个筷子，加一个锁")
        lock_b.acquire()
        print("A加第二个锁，强盗第二根筷子，吃一口饭")
        lock_b.release()
        print("A释放锁，放下第二根筷子")
        lock_a.release()
        print("A加第一个锁，抢到第一根筷子")
def PersonB():
    for i in range(100):
        lock_a.acquire()
        print("B抢到第一个筷子，加一个锁")
        lock_b.acquire()
        print("B加第二个锁，强盗第二根筷子，吃一口饭")
        lock_b.release()
        print("B释放锁，放下第二根筷子")
        lock_a.release()
        print("B加第一个锁，抢到第一根筷子")
if __name__ == '__main__':
    pa = threading.Thread(target=PersonA)
    pb = threading.Thread(target=PersonB)
    pa.start()
    pb.start()

结语

python的部分快要结束了，后面要更新linux服务器和k8s的笔记，希望大家多多👍