线程

概念

线程时最小的执行单元，依赖于进程，是一个 CPU 执行时所需要的一串指令。

分类

主线程、子线程、守护线程

创建线程

方法一：将函数作为参数传入threading.Thread中

    import threading,time#导入threading模块  

    def run(a):#以随意定义方法,不一定是run  
        time.sleep(2)  
        print('this is thread%d'%a)  


    thread_list=[]#定义空列表  
    for i in range(10):  
        t=threading.Thread(target=run, args=[i, ])#初始化线程  
        thread_list.append(t)#将初始化的线程添加到列表中  

    for item in thread_list:#批量开启线程  
        item.start()

结果：

2秒后出现以下

    this is thread0  
    this is thread1  
    this is thread6  
    this is thread5  
    this is thread3  
    this is thread4  
    this is thread2  
    this is thread8  
    this is thread7  
    this is thread9  

    Process finished with exit code 0

方法二：定义一个类，继承threading.thread,重写run方法

    import threading,time#导入threading模块  

    class mythread(threading.Thread):  
        def __init__(self,n):  
            super(mythread, self).__init__()  # 重构run函数必须要写  
            self.n=n  
        def run(self):#这里只能是run方法，不要和上面搞混了，上面可以随意定义方法  
            time.sleep(2)  
            print('this is thread%d' % self.n)  

    if __name__=="__main__":  
        thread_list = []  # 定义空列表  
        for i in range(10):  
            t=mythread(i)  
            thread_list.append(t)  

        for item in thread_list:  # 批量开启线程  
            item.start()

结果：

2s后出现以下

    this is thread2  
    this is thread3  
    this is thread0  
    this is thread1  
    this is thread8  
    this is thread7  
    this is thread6  
    this is thread4  
    this is thread5  
    this is thread9  

    Process finished with exit code 0

join方法

使线程执行完才结束

守护线程

setDaemon(),主线程执行完就结束

线程锁

很多线程同时修改1个数据时，容易出错，此时给线程加一把锁，即该线程在执行某项操作时，别的线程不可执行，直至解锁后别的线程才能执行该项操作

    import threading,time#导入threading模块  

    lock=threading.Lock()#定义一把线程锁  

    num=0  

    class mythread(threading.Thread):  
        def run(self):  
            lock.acquire()#锁上  
            global num  
            num=num+1  
            lock.release()#打开  

    list=[]  
    for i in range(100000):  
        t=mythread()  
        list.append(t)  
    for item in list:  
        item.start()  

    print(num)#打印结果

结果:

    100000  

    Process finished with exit code 0

递归锁

threading.Lock()只能锁一层，不能锁上锁。threading.RLock()可以在锁内再锁。