python基础===多线程

https://www.cnblogs.com/wj-1314/p/8263328.html

threading 模块

先上代码：

import time, threading

def loop():
    print("thread %s is running..." %threading.current_thread().name)
    n = 0
    while n<5:
        n += 1
        print('thread %s >>> %s'%(threading.current_thread().name, n))
        time.sleep(1)
    print("thread %s ended." %threading.current_thread().name)

def loop1():
    x = 1
    while x <3:
        print(x,"loop1的线程")
        x += 1
        time.sleep(2)

if __name__ == "__main__":
    print("thread %s is running ..." %threading.current_thread().name)
    t = threading.Thread(target = loop, name = "LoopThread")
    t1 = threading.Thread(target = loop1)
    t.start()
    t1.start()
    t.join()
    t1.join()
    print("thread %s ended." % threading.current_thread().name)
    

"""
thread MainThread is running ...
thread LoopThread is running...1
thread LoopThread >>> 1
loop1的线程
thread LoopThread >>> 2
2thread LoopThread >>> 3 
loop1的线程
thread LoopThread >>> 4
thread LoopThread >>> 5
thread LoopThread ended.
thread MainThread ended.
 
"""

由于任何进程默认就会启动一个线程，我们把该线程称为主线程，主线程又可以启动新的线程，Python的threading模块有个threading.current_thread() 获取当前线程的实例。

但是有些情况下，多线程会产生场景上的错误，比如

import time, threading

# 假定这是你的银行存款:
balance = 0

def change_it(n):
    # 先存后取，结果应该为0:
    global balance
    balance = balance + n
    balance = balance - n

def run_thread(n):
    for i in range(100000):
        change_it(n)

t1 = threading.Thread(target=run_thread, args=(5,))
t2 = threading.Thread(target=run_thread, args=(8,))
t1.start()
t2.start()
t1.join()
t2.join()
print(balance)

结果有时会报错

如果我们要确保balance计算正确，就要给change_it()上一把锁，当某个线程开始执行change_it()时，我们说，该线程因为获得了锁，因此其他线程不能同时执行change_it()，只能等待，直到锁被释放后，获得该锁以后才能改。由于锁只有一个，无论多少线程，同一时刻最多只有一个线程持有该锁，所以，不会造成修改的冲突。创建一个锁就是通过threading.Lock()来实现：

import time, threading
lock = threading.Lock()

# 假定这是你的银行存款:
balance = 0

def change_it(n):
    # 先存后取，结果应该为0:
    global balance
    balance = balance + n
    balance = balance - n

def run_thread(n):
    for i in range(100000):

        lock.acquire()
        try:
            change_it(n)
        finally:
            lock.release()
            

t1 = threading.Thread(target=run_thread, args=(5,))
t2 = threading.Thread(target=run_thread, args=(8,))
t1.start()
t2.start()
t1.join()
t2.join()
print(balance)