一、介绍
线程是什么？线程有啥用？线程和进程的区别是什么？
线程是操作系统能够进行运算调度的最小单位。被包含在进程中，是进程中的实际运作单位。一条线程指的是进程中一个单一顺序的控制流，一个进程中可以并发多个线程，每条线程并行执行不同的任务。
二、Python如何创建线程
2.1 方法一：
创建Thread对象
步骤：
1.目标函数
2.实例化Thread对象
3.调用start()方法
import threading
# 目标函数1
def fun1(num):
for i in range(num):
print('线程1: 第%d次循环:' % i)
# 目标函数2
def fun2(lst):
for ele in lst:
print('线程2: lst列表中元素 %d' % ele)
def main():
num = 10
# 实例化Thread对象
# target参数一定为一个函数，且不带括号
# args参数为元组类型，参数为一个时一定要加逗号
t1 = threading.Thread(target=fun1, args=(num,))
t2 = threading.Thread(target=fun2, args=([1, 2, 3, 4, 5],))
# 调用start方法
t1.start()
t2.start()
if __name__ == '__main__':
main()
2.2 方法二：
创建子类继承threading.Thread类
import threading
import os
class Person(threading.Thread):
def run(self):
self.sing(5)
self.cook()
@staticmethod
def sing(num):
for i in range(num):
print('线程[%d]: The person sing %d song.' % (os.getpid(), i))
@staticmethod
def cook():
print('线程[%d]:The person has cooked breakfast.' % os.getpid())
def main():
p1 = Person()
p1.start()
p2 = Person()
p2.start()
if __name__ == '__main__':
main()
三、线程的用法
3.1 确定当前的线程
import threading
import time
import logging
def fun1():
print(threading.current_thread().getName(), 'starting')
time.sleep(0.2)
print(threading.current_thread().getName(), 'exiting')
def fun2():
# print(threading.current_thread().getName(), 'starting')
# time.sleep(0.3)
# print(threading.current_thread().getName(), 'exiting')
logging.debug('starting')
time.sleep(0.3)
logging.debug('exiting')
logging.basicConfig(
level=logging.DEBUG,
format='[%(levelname)s] (%(threadName)-10s) %(message)s'
)
def main():
t1 = threading.Thread(name='线程1', target=fun1)
t2 = threading.Thread(name='线程2', target=fun2)
t1.start()
t2.start()
if __name__ == '__main__':
main()
3.2 守护线程
区别
- 普通线程：主线程等待子线程关闭后关闭
- 守护线程：管你子线程关没关，主线程到时间就关闭
守护线程如何搞
- 方法1：构造线程时传入dameon=True
- 方法2：调用setDaemon()方法并提供参数True
import threading
import time
import logging
def daemon():
logging.debug('starting')
# 添加延时，此时主线程已经退出，exiting不会打印
time.sleep(0.2)
logging.debug('exiting')
def non_daemon():
logging.debug('starting')
logging.debug('exiting')
logging.basicConfig(
level=logging.DEBUG,
format='[%(levelname)s] (%(threadName)-10s) %(message)s'
)
def main():
# t1 = threading.Thread(name='线程1', target=daemon)
# t1.setDaemon(True)
t1 = threading.Thread(name='线程1', target=daemon, daemon=True)
t2 = threading.Thread(name='线程2', target=non_daemon)
t1.start()
t2.start()
# 等待守护线程完成工作需要调用join()方法，默认情况join会无限阻塞，可以传入浮点值，表示超时时间
t1.join(0.2)
t2.join(0.1)
if __name__ == '__main__':
main()
3.3 控制资源访问
目的：
Python线程中资源共享，如果不对资源加上互斥锁，有可能导致数据不准确。
import threading
import time
g_num = 0
def fun1(num):
global g_num
for i in range(num):
g_num += 1
print('线程1 g_num = %d' % g_num)
def fun2(num):
global g_num
for i in range(num):
g_num += 1
print('线程2 g_num = %d' % g_num)
def main():
t1 = threading.Thread(target=fun1, args=(1000000,))
t2 = threading.Thread(target=fun1, args=(1000000,))
t1.start()
t2.start()
if __name__ == '__main__':
main()
time.sleep(1)
print('主线程 g_num = %d' % g_num)
互斥锁
import threading
import time
g_num = 0
L = threading.Lock()
def fun1(num):
global g_num
L.acquire()
for i in range(num):
g_num += 1
L.release()
print('线程1 g_num = %d' % g_num)
def fun2(num):
global g_num
L.acquire()
for i in range(num):
g_num += 1
L.release()
print('线程2 g_num = %d' % g_num)
def main():
t1 = threading.Thread(target=fun1, args=(1000000,))
t2 = threading.Thread(target=fun1, args=(1000000,))
t1.start()
t2.start()
if __name__ == '__main__':
main()
time.sleep(1)
print('主线程 g_num = %d' % g_num)
互斥锁引发的另一个问题：死锁
死锁产生的原理：
import threading
import time
g_num = 0
L1 = threading.Lock()
L2 = threading.Lock()
def fun1():
L1.acquire(timeout=5)
time.sleep(1)
L2.acquire()
print('产生死锁，并不会打印信息')
L2.release()
L1.release()
def fun2():
L2.acquire(timeout=5)
time.sleep(1)
L1.acquire()
print('产生死锁，并不会打印信息')
L1.release()
L2.release()
def main():
t1 = threading.Thread(target=fun1)
t2 = threading.Thread(target=fun2)
t1.start()
t2.start()
if __name__ == '__main__':
main()
time.sleep(1)
print('主线程 g_num = %d' % g_num)
如何避免产生死锁：
锁超时操作
import threading
import time
g_num = 0
L1 = threading.Lock()
L2 = threading.Lock()
def fun1():
L1.acquire()
time.sleep(1)
L2.acquire(timeout=5)
print('超时异常打印信息1')
L2.release()
L1.release()
def fun2():
L2.acquire()
time.sleep(1)
L1.acquire(timeout=5)
print('超时异常打印信息2')
L1.release()
L2.release()
def main():
t1 = threading.Thread(target=fun1)
t2 = threading.Thread(target=fun2)
t1.start()
t2.start()
if __name__ == '__main__':
main()
time.sleep(1)
print('主线程 g_num = %d' % g_num)
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