多线程 #Python

join.py

# 调用join表示自身优先执行


import threading
#定义线程要调用的方法，*add可接收多个以非关键字方式传入的参数
def action(*add):
    for arc in add:
        #调用 getName() 方法获取当前执行该程序的线程名
        print(threading.current_thread().getName() +" "+ arc)
#定义为线程方法传入的参数
my_tuple = ("http://c.biancheng.net/python/",\
            "http://c.biancheng.net/shell/",\
            "http://c.biancheng.net/java/")
#创建线程
thread = threading.Thread(target = action,args =my_tuple)
#启动线程
thread.start()
#指定 thread 线程优先执行完毕
thread.join()
#主线程执行如下语句
for i in range(5):
    print(threading.current_thread().getName())
    
    
# 结果：
'''
Thread-1 http://c.biancheng.net/python/
Thread-1 http://c.biancheng.net/shell/
Thread-1 http://c.biancheng.net/java/
MainThread
MainThread
MainThread
MainThread
MainThread
'''


# 不使用join


import threading
#定义线程要调用的方法，*add可接收多个以非关键字方式传入的参数
def action(*add):
    for arc in add:
        #调用 getName() 方法获取当前执行该程序的线程名
        print(threading.current_thread().getName() +" "+ arc)
#定义为线程方法传入的参数
my_tuple = ("http://c.biancheng.net/python/",\
            "http://c.biancheng.net/shell/",\
            "http://c.biancheng.net/java/")
#创建线程
thread = threading.Thread(target = action,args =my_tuple)
#启动线程
thread.start()
#主线程执行如下语句
for i in range(5):
    print(threading.current_thread().getName())
    

# 结果：

'''
Thread-1 http://c.biancheng.net/python/
MainThread
Thread-1 http://c.biancheng.net/shell/
MainThread
Thread-1 http://c.biancheng.net/java/
MainThread
MainThread
MainThread
'''

lock.py

import threading
balance = 0
def change_it_without_lock(n):
    global balance
    # 不加锁的话 最后的值不是0
    # 线程共享数据危险在于 多个线程同时改同一个变量
    # 如果每个线程按顺序执行，那么值会是0， 但是线程时系统调度，又不确定性，交替进行
    # 没锁的话，同时修改变量
    # 所以加锁是为了同时只有一个线程再修改，别的线程表一定不能改
    for i in range(100000):
        balance = balance + n
        balance = balance - n

threads = [
    threading.Thread(target=change_it_without_lock, args=(8,) ),
    threading.Thread(target=change_it_without_lock, args=(10,) )
]

[t.start() for t in threads]
[t.join() for t in threads]

print(balance)


# 不加锁输出结果：

'''
(py36) ➜  MultipleCameras python lock.py
0
(py36) ➜  MultipleCameras python lock.py
0
(py36) ➜  MultipleCameras python lock.py
0
(py36) ➜  MultipleCameras python lock.py
8
(py36) ➜  MultipleCameras python lock.py
0
'''

thread1.py

# 意义不明的代码
import threading
import time

def test(k):
    for i in range(k):
        print('test ',i)
        # time.sleep(1)


thread = threading.Thread(target=test, args=(6,))
thread.start()

for i in range(5):
    print('main ', i)
    # time.sleep(1)

# 打印结果，每次打印都不一样
'''
test  0
main  0
test  1
main  1
main  2
main  3
main  4
test  2
test  3
test  4
test  5
'''