python threading 锁的应用

如果多个线程共同对某个数据修改，则可能出现不可预料的结果，为了保证数据的正确性，需要对多个线程进行同步。使用 Thread 对象的 Lock 和 Rlock 可以实现简单的线程同步，这两个对象都有 acquire 方法和 release 方法，对于那些需要每次只允许一个线程操作的数据，可以将其操作放到 acquire 和 release 方法之间。锁有两种状态——锁定和未锁定。每当一个线程比如"set"要访问共享数据时，必须先获得锁定；如果已经有别的线程比如"print"获得锁定了，那么就让线程"set"暂停，也就是同步阻塞；等到线程"print"访问完毕，释放锁以后，再让线程"set"继续。

一、（1）未采用锁，线程1与线程2并行执行。

import threading
from time import sleep,ctime

class MyThread(threading.Thread):
    def __init__(self, func, arg):
        super(MyThread, self).__init__()
        self.func = func
        self.arg = arg
    # 重写run()方法
    def run(self):
        """
        threadLock.acquire() #获取锁，用于线程同步
        """
        self.func(self.arg)

        """
        threadLock.release()#释放锁，开启下一个线程
        """

def f(n):
    for i in range(n):
        sleep(1)
        print(i,threading.current_thread().name,ctime())

"""
threadLock = threading.Lock()
"""

for i in range(2):
    thread = MyThread(f,5)
    thread.start()

输出如下：

00  Thread-1Thread-2  Mon Oct 26 19:52:12 2020Mon Oct 26 19:52:12 2020

11  Thread-1 Thread-2Mon Oct 26 19:52:13 2020 
Mon Oct 26 19:52:13 2020
22  Thread-1Thread-2  Mon Oct 26 19:52:14 2020Mon Oct 26 19:52:14 2020

33  Thread-1Thread-2  Mon Oct 26 19:52:15 2020Mon Oct 26 19:52:15 2020

44  Thread-2Thread-1  Mon Oct 26 19:52:16 2020Mon Oct 26 19:52:16 2020

（2）采用锁，先执行线程1，后执行线程2.

import threading
from time import sleep,ctime

class MyThread(threading.Thread):
    def __init__(self, func, arg):
        super(MyThread, self).__init__()
        self.func = func
        self.arg = arg
    # 重写run()方法
    def run(self):
        
        threadLock.acquire() #获取锁，用于线程同步
        
        self.func(self.arg)
        
        threadLock.release()#释放锁，开启下一个线程
        

def f(n):
    for i in range(n):
        sleep(1)
        print(i,threading.current_thread().name,ctime())


threadLock = threading.Lock()


for i in range(2):
    thread = MyThread(f,5)
    thread.start()

输出如下：

0 Thread-1 Mon Oct 26 19:59:17 2020
1 Thread-1 Mon Oct 26 19:59:18 2020
2 Thread-1 Mon Oct 26 19:59:19 2020
3 Thread-1 Mon Oct 26 19:59:20 2020
4 Thread-1 Mon Oct 26 19:59:21 2020
0 Thread-2 Mon Oct 26 19:59:22 2020
1 Thread-2 Mon Oct 26 19:59:23 2020
2 Thread-2 Mon Oct 26 19:59:24 2020
3 Thread-2 Mon Oct 26 19:59:25 2020
4 Thread-2 Mon Oct 26 19:59:26 2020

应用所阻塞子线程的执行，应用join阻塞主线程的执行。

import threading
from time import sleep,ctime

class MyThread(threading.Thread):
    def __init__(self, func, arg):
        super(MyThread, self).__init__()
        self.func = func
        self.arg = arg
    # 重写run()方法
    def run(self):
        threadLock.acquire() #获取锁，用于线程同步
        self.func(self.arg)
        threadLock.release()#释放锁，开启下一个线程
        
number=0
def f(n):
    global number
    for i in range(n):
        number+=1
    print(number,threading.current_thread().name,ctime())


threadLock = threading.Lock()

threads=[]
for i in range(10):
    thread = MyThread(f,10)
    threads.append(thread)

for t in threads:
    t.start()
    t.join()


print(number,threading.current_thread().name,ctime())

输出如下：

10 Thread-1 Mon Oct 26 20:09:59 2020
20 Thread-2 Mon Oct 26 20:09:59 2020
30 Thread-3 Mon Oct 26 20:09:59 2020
40 Thread-4 Mon Oct 26 20:09:59 2020
50 Thread-5 Mon Oct 26 20:09:59 2020
60 Thread-6 Mon Oct 26 20:09:59 2020
70 Thread-7 Mon Oct 26 20:09:59 2020
80 Thread-8 Mon Oct 26 20:09:59 2020
90 Thread-9 Mon Oct 26 20:09:59 2020
100 Thread-10 Mon Oct 26 20:09:59 2020
100 MainThread Mon Oct 26 20:09:59 2020