• Python中的多线程


    1、什么是线程

      进程其实不是一个执行单位,进程是一个资源单位

      每个进程内自带一个线程,线程才是CPU上的执行单位

      

    如果把操作系统比喻为一座工厂

      在工厂内每造出一个车间===》启动一个进程

      每个车间内至少有一条流水线===》每个进程内至少有一个线程

    线程==》单指代码的执行过程

    进程==》资源的申请与销毁的过程

    2、进程VS线程

      1)内存共享or隔离

        多个进程内存空间彼此隔离

        同一进程下的多个线程共享该进程内的数据

      2)创建速度

        造线程的速度要远远快于造进程

    一、开启线程的两种方式(重点)

    
    
    方式一:导入Thread模块

    1
    from threading import Thread 2 import time 3 5 def task(name): 6 print('%s is running' %name) 7 time.sleep(3) 8 print('%s is done' %name) 9 if __name__ == '__main__': 10 t=Thread(target=task,args=('子线程',)) 11 t.start() 12 print('')
    
    
    方式二:创建类继承Thread

    1
    from threading import Thread 2 import time 3 4 6 # class Mythread(Thread): 7 # def run(self): 8 # print('%s is running' %self.name) 9 # time.sleep(3) 10 # print('%s is done' %self.name) 11 # 12 # if __name__ == '__main__': 13 # t=Mythread() 14 # t.start() 15 # print('主')

    二、线程VS进程(重点)

     1 # from threading import Thread
     2 # from multiprocessing import Process
     3 # import time
     4 #
     5 # def task(name):
     6 #     print('%s is running' %name)
     7 #     time.sleep(3)
     8 #     print('%s is done' %name)
     9 #
    10 # if __name__ == '__main__':
    11 #     t=Thread(target=task,args=('子线程',))
    12 #     # t=Process(target=task,args=('子进程',))
    13 #     t.start()
    14 #     print('主')

    线程运行结果:

    进程运行结果:

     2)同一进程下的多个线程共享该进程内的数据(了解知识点)

     1 # from threading import Thread
     2 # import time
     3 #
     4 # x=100
     5 # def task():
     6 #     global x
     7 #     x=0
     8 #
     9 # if __name__ == '__main__':
    10 #     t=Thread(target=task,)
    11 #     t.start()
    12 #     # time.sleep(3)
    13 #     t.join()
    14 #     print('主',x)
    View Code

    3)查看pid(了解知识点)

    注意:一个进程中的子线程pid相同

     1 from threading import Thread
     2 import time,os
     3 
     4 def task():
     5     print(os.getpid())
     6 
     7 if __name__ == '__main__':
     8     t=Thread(target=task,)
     9     t.start()
    10     print('',os.getpid())
    View Code

     三、线程对象的其他方法和属性(熟悉知识点)

    1)主进程等子进程是因为主进程要给子进程收尸

    2)进程必须等待其内部所有线程都运行完毕才结束

     1 # from threading import Thread
     2 # import time
     3 #
     4 # def task(name):
     5 #     print('%s is running' %name)
     6 #     time.sleep(3)
     7 #     print('%s is done' %name)
     8 # if __name__ == '__main__':
     9 #     t=Thread(target=task,args=('子线程',))
    10 #     t.start()
    11 #     print('主')
    12 #
    View Code
     1 from threading import Thread,current_thread,active_count,enumerate
     2 import time
     3 
     4 
     5 def task():
     6     print('%s is running' % current_thread().name)
     7     time.sleep(3)
     8     print('%s is done' % current_thread().name)
     9 
    10 
    11 if __name__ == '__main__':
    12     t = Thread(target=task,name='xxx')
    13     t.start()
    14     # t.join()
    15     # print(t.is_alive())
    16     # print(t.getName())
    17     # print(t.name)
    18     # print('主',active_count())
    19     # print(enumerate())
    20 
    21     # t.join()
    22     current_thread().setName('主线程')
    23     print('',current_thread().name)
    View Code

    四、守护线程(熟悉知识点)

    守护线程(daemon)会在本进程内所有非守护的线程都死掉了才跟着死

    即:

      守护线程其实守护的是整个进程的运行周期(进程内所有的非守护线程都运行完毕)

     1 # from threading import Thread,current_thread
     2 # import time
     3 #
     4 #
     5 # def task():
     6 #     print('%s is running' % current_thread().name)
     7 #     time.sleep(3)
     8 #     print('%s is done' % current_thread().name)
     9 #
    10 #
    11 # if __name__ == '__main__':
    12 #     t = Thread(target=task,name='守护线程')
    13 #     t.daemon=True
    14 #     t.start()
    15 #     print('主')
    守护进程
     1 from threading import Thread
     2 import time
     3 def foo():
     4     print(123)
     5     time.sleep(3)
     6     print("end123")
     7 
     8 def bar():
     9     print(456)
    10     time.sleep(1)
    11     print("end456")
    12 
    13 
    14 t1=Thread(target=foo)
    15 t2=Thread(target=bar)
    16 
    17 t1.daemon=True
    18 t1.start()
    19 t2.start()
    20 print("main-------")
    21 
    22 '''
    23 123
    24 456
    25 main-------
    26 end456
    27 
    28 '''
    较迷惑人的守护进程

    五、互斥锁(熟悉知识点)

     1 from threading import Thread,Lock
     2 import time
     3 
     4 mutex=Lock()
     5 
     6 x=100
     7 def task():
     8     global x
     9     # mutex.acquire()
    10     temp=x
    11     time.sleep(0.1)
    12     x=temp-1
    13     # mutex.release()
    14 
    15 if __name__ == '__main__':
    16     t_l=[]
    17     start=time.time()
    18     for i in range(100):
    19         t=Thread(target=task)
    20         t_l.append(t)
    21         t.start()
    22 
    23     for t in t_l:
    24         t.join()
    25 
    26     stop=time.time()
    27     print(x,stop-start)
    互斥锁

    六、死锁现象与递归锁(熟悉知识点)

      如果用Lock(互斥锁),会发生死锁现象

      递归锁本质是一把锁,可连续acqruie,但只有其上的计数为0时其他线程才可对其调用

     1 from threading import Thread,Lock,active_count,RLock
     2 import time
     3 
     4 # mutexA=Lock()
     5 # mutexB=Lock()
     6 obj=RLock() #递归锁的特点:可以连续的acquire
     7 mutexA=obj
     8 mutexB=obj
     9 
    10 class Mythread(Thread):
    11     def run(self):
    12         self.f1()
    13         self.f2()
    14 
    15     def f1(self):
    16         mutexA.acquire()
    17         print('%s 拿到A锁' %self.name)
    18 
    19         mutexB.acquire()
    20         print('%s 拿到B锁' %self.name)
    21         mutexB.release()
    22 
    23         mutexA.release()
    24 
    25     def f2(self):
    26         mutexB.acquire()
    27         print('%s 拿到B锁' %self.name)
    28         time.sleep(1)
    29 
    30         mutexA.acquire()
    31         print('%s 拿到A锁' %self.name)
    32         mutexA.release()
    33 
    34         mutexB.release()
    35 
    36 if __name__ == '__main__':
    37     for i in range(10):
    38         t=Mythread()
    39         t.start()
    40     # print(active_count())
    View Code

    七、信号量(熟悉知识点)

      信号量本质上还是锁,但区别信号量是控制同一时刻并发执行的任务数

     1 from threading import Thread,Semaphore,current_thread
     2 import time,random
     3 
     4 sm=Semaphore(5)
     5 
     6 def task():
     7     with sm:
     8         print('%s 正在上厕所' %current_thread().name)
     9         time.sleep(random.randint(1,4))
    10 
    11 
    12 if __name__ == '__main__':
    13     for i in range(20):
    14         t=Thread(target=task)
    15         t.start()
    信号量
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  • 原文地址:https://www.cnblogs.com/huyingsakai/p/9305912.html
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