一、线程
01 什么是线程
进程其实不是一个执行单位，进程是一个资源单位
每个进程内自带一个线程，线程才是cpu上的执行单位
如果把操作系统比喻为一座工厂
在工厂内每造出一个车间===》启动一个进程
每个车间内至少有一条流水线===》每个进程内至少有一个线程
线程=》单指代码的执行过程
进程-》资源的申请与销毁的过程
开启线程的两种方式：
from threading import Thread
import time
#方式一
def task(name):
print('%s is running' %name)
time.sleep(3)
print('%s is done' %name)
if __name__ == '__main__':
t=Thread(target=task,args=('子线程',))
t.start()
print('主')
方式二
class Mythread(Thread):
def run(self):
print('%s is running' %self.name)
time.sleep(3)
print('%s is done' %self.name)
if __name__ == '__main__':
t=Mythread()
t.start()
print('主')
02 进程vs线程
1、内存共享or隔离
多个进程内存空间彼此隔离
同一进程下的多个线程共享该进程内的数据
from threading import Thread
import time
x=100
def task():
global x
x=0
if __name__ == '__main__':
t=Thread(target=task,)
t.start()
# time.sleep(3)
t.join()
print('主',x)
2、创建速度
造线程的速度要远远快于造进程
1、线程的开启速度快
from threading import Thread
from multiprocessing import Process
import time
def task(name):
print('%s is running' %name)
time.sleep(3)
print('%s is done' %name)
if __name__ == '__main__':
t=Thread(target=task,args=('子线程',))
# t=Process(target=task,args=('子进程',))
t.start()
print('主')
3、 查看pid
from threading import Thread
import time,os
def task():
print(os.getpid())
if __name__ == '__main__':
t=Thread(target=task,)0
t.start()
print('主',os.getpid())
03.线程对象的其他方法和属性
主进程等子进程是因为主进程要给子进程收尸
进程必须等待其内部所有线程都运行完毕才结束
from threading import Thread,current_thread,active_count,enumerate
import time
def task():
print('%s is running' % current_thread().name)
time.sleep(3)
print('%s is done' % current_thread().name)
if __name__ == '__main__':
t = Thread(target=task,name='xxx')
t.start()
# t.join()
# print(t.is_alive())
# print(t.getName())
# print(t.name)
# print('主',active_count())
# print(enumerate())
# t.join()
current_thread().setName('主线程')
print('主',current_thread().name)
04、守护线程
守护线程会在本进程内所有非守护的线程都死掉了才跟着死
即：守护线程其实守护的是整个进程的运行周期（进程内所有的非守护线程都运行完毕）
from threading import Thread
import time
def foo():
print(123)
time.sleep(3)
print("end123")
def bar():
print(456)
time.sleep(1)
print("end456")
t1=Thread(target=foo)
t2=Thread(target=bar)
t1.daemon=True
t1.start()
t2.start()
print("main-------")
'''
123
456
main-------
end456
'''
05、互斥锁
from threading import Thread,Lock
import time
mutex=Lock()
x=100
def task():
global x
# mutex.acquire()
temp=x
time.sleep(0.1)
x=temp-1
# mutex.release()
if __name__ == '__main__':
t_l=[]
start=time.time()
for i in range(100):
t=Thread(target=task)
t_l.append(t)
t.start()
for t in t_l:
t.join()
stop=time.time()
print(x,stop-start)
06、死锁现象与递归锁
from threading import Thread,Lock,active_count,RLock
import time
# mutexA=Lock()
# mutexB=Lock()
obj=RLock() #递归锁的特点：可以连续的acquire
mutexA=obj
mutexB=obj
class Mythread(Thread):
def run(self):
self.f1()
self.f2()
def f1(self):
mutexA.acquire()
print('%s 拿到A锁' %self.name)
mutexB.acquire()
print('%s 拿到B锁' %self.name)
mutexB.release()
mutexA.release()
def f2(self):
mutexB.acquire()
print('%s 拿到B锁' %self.name)
time.sleep(1)
mutexA.acquire()
print('%s 拿到A锁' %self.name)
mutexA.release()
mutexB.release()
if __name__ == '__main__':
for i in range(10):
t=Mythread()
t.start()
# print(active_count())
07、信号量
信号量是控制同一时刻并发执行的任务数
from threading import Thread,Semaphore,current_thread
import time,random
sm=Semaphore(5)
def task():
with sm:
print('%s 正在上厕所' %current_thread().name)
time.sleep(random.randint(1,4))
if __name__ == '__main__':
for i in range(20):
t=Thread(target=task)
t.start()