目錄
- 一、介紹
- 二、Python如何創建線程
- 三、線程的用法
- 3.1 確定當前的線程
- 3.2 守護線程
- 3.3 控制資源訪問
一、介紹
線程是什么？線程有啥用？線程和進程的區別是什么？
線程是操作系統能夠進行運算調度的最小單位。被包含在進程中，是進程中的實際運作單位。一條線程指的是進程中一個單一順序的控制流，一個進程中可以并發多個線程，每條線程并行執行不同的任務。
二、Python如何創建線程
2.1 方法一：
創建Thread對象
步驟：
1.目標函數
2.實例化Thread對象
3.調用start()方法
import threading
# 目標函數1
def fun1(num):
for i in range(num):
print('線程1: 第%d次循環:' % i)
# 目標函數2
def fun2(lst):
for ele in lst:
print('線程2: lst列表中元素 %d' % ele)
def main():
num = 10
# 實例化Thread對象
# target參數一定為一個函數，且不帶括號
# args參數為元組類型，參數為一個時一定要加逗號
t1 = threading.Thread(target=fun1, args=(num,))
t2 = threading.Thread(target=fun2, args=([1, 2, 3, 4, 5],))
# 調用start方法
t1.start()
t2.start()
if __name__ == '__main__':
main()
2.2 方法二：
創建子類繼承threading.Thread類
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('線程[%d]: The person sing %d song.' % (os.getpid(), i))
@staticmethod
def cook():
print('線程[%d]:The person has cooked breakfast.' % os.getpid())
def main():
p1 = Person()
p1.start()
p2 = Person()
p2.start()
if __name__ == '__main__':
main()
三、線程的用法
3.1 確定當前的線程
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='線程1', target=fun1)
t2 = threading.Thread(name='線程2', target=fun2)
t1.start()
t2.start()
if __name__ == '__main__':
main()
3.2 守護線程
區別
- 普通線程：主線程等待子線程關閉后關閉
- 守護線程：管你子線程關沒關，主線程到時間就關閉
守護線程如何搞
- 方法1：構造線程時傳入dameon=True
- 方法2：調用setDaemon()方法并提供參數True
import threading
import time
import logging
def daemon():
logging.debug('starting')
# 添加延時，此時主線程已經退出，exiting不會打印
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='線程1', target=daemon)
# t1.setDaemon(True)
t1 = threading.Thread(name='線程1', target=daemon, daemon=True)
t2 = threading.Thread(name='線程2', target=non_daemon)
t1.start()
t2.start()
# 等待守護線程完成工作需要調用join()方法，默認情況join會無限阻塞，可以傳入浮點值，表示超時時間
t1.join(0.2)
t2.join(0.1)
if __name__ == '__main__':
main()
3.3 控制資源訪問
目的：
Python線程中資源共享，如果不對資源加上互斥鎖，有可能導致數據不準確。
import threading
import time
g_num = 0
def fun1(num):
global g_num
for i in range(num):
g_num += 1
print('線程1 g_num = %d' % g_num)
def fun2(num):
global g_num
for i in range(num):
g_num += 1
print('線程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('主線程 g_num = %d' % g_num)
互斥鎖
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('線程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('線程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('主線程 g_num = %d' % g_num)
互斥鎖引發的另一個問題：死鎖
死鎖產生的原理：
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('產生死鎖，并不會打印信息')
L2.release()
L1.release()
def fun2():
L2.acquire(timeout=5)
time.sleep(1)
L1.acquire()
print('產生死鎖，并不會打印信息')
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('主線程 g_num = %d' % g_num)
如何避免產生死鎖：
鎖超時操作
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('超時異常打印信息1')
L2.release()
L1.release()
def fun2():
L2.acquire()
time.sleep(1)
L1.acquire(timeout=5)
print('超時異常打印信息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('主線程 g_num = %d' % g_num)
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