Python 线程复习

修改全局变量，设立flag来避免线程间数据冲突，低效率版

from threading import Thread
import time
 
g_num=0
g_flag = 1
 
def test1():
    global g_num
    global g_flag
    if g_flag ==1:
        for i in range(1000000):
            g_num += 1 
 
        g_flag = 0
    print('----test1----g_num=%d'%g_num)
 
def test2():
    global g_num
    global g_flag
    while True:
        if g_flag != 1:
            for i in range(1000000):
                g_num += 1
            break
 
    print('----test2----g_num=%d' % g_num)
p1 = Thread(target=test1)
p1.start()
 
p2 = Thread(target=test2)
p2.start()

修改全局变量，互斥锁（高效版），否则不用枷锁

from threading import Thread,Lock
import time
 
g_num=0
 
def test1():
    global g_num
    for i in range(1000000):
        mutex.acquire()  # 上锁
        g_num += 1
        mutex.release() #解锁
    print('----test1----g_num=%d'%g_num)
 
def test2():
    global g_num
    for i in range(1000000):
        mutex.acquire()  # 上锁
        g_num += 1
        mutex.release()  # 解锁
 
    print('----test2----g_num=%d' % g_num)
 
mutex = Lock()
 
p1 = Thread(target=test1)
p1.start()
 
p2 = Thread(target=test2)
p2.start()

死锁

添加超时时间 mutex.acquire(timeout = 1)

银行家算法-先满足最小需求单位，等待

 ThreadLocal

可以解决线程间全局变量，不会因为线程修改全局变量而修改，完成数据间传递，不会因为程序一样而导致数据错乱

代码如下：

import threading
 
# 创建全局变量threadLocal
loacl_school = threading.local()
 
def process_student():
    # 获取当前线程关联的student
    std = loacl_school.student
    print(std)
 
def process_thrad(name):
    # 绑定threadlocal的student
    loacl_school.student = name
    process_student()
 
t1 = threading.Thread(target=process_thrad,args=('laowang',),name='thread-a')
t2 = threading.Thread(target=process_thrad,args=('xiaowang',),name='thread-b')
 
t1.start()
t2.start()
 
t1.join()
t2.join()

 异步

callback=func,并把之前函数返回值复制到func

GIL 全局解释器锁

解决办法：1、用多进程2、用C语言写关键部分

python部分

from ctypes import *
from threading import Thread
 
# 加载动态库
lib = cdll.LoadLibrary('./libdeadloop.so')
 
#创建一个子线程，让其执行C语言编写的函数，此函数是一个死循环
t = Thread(target=lib.DeadLoop)
t.start()
 
# 主线程页调用C语言写的那个死循环函数
lib.DeadLoop()
 
while True:
    pass

C语言代码

{
    while(){
        ;
    }

}

生成libdealloop.so库

线程同步

import threading
 
mylock = threading.RLock()
num = 0
 
class myThread(threading.Thread):
    def __init__(self,name):
        threading.Thread.__init__(self,name=name)
 
    def run(self):
        global num
        while True:
            mylock.acquire()
            print('%s locked,Number:%d'% (threading.current_thread().name,num))
            if num>=4:
                mylock.release()
                print('%s locked,Number:%d'% (threading.current_thread().name,num))
                break
            num+=1
            print('%s locked,Number:%d'% (threading.current_thread().name,num))
            mylock.release()
 
if __name__ =='__main__':
    thread1 = myThread('Thread_1')
    thread2 = myThread('Thread_2')
    thread1.start()
    thread2.start()