多线程《三》进程与线程的区别

#1 进程的开销大于线程
# from threading import Thread
# 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=('alex',))           #元祖形式
#     t.start()
#     print('主线程')         #alex is running 主进程 几乎是同时打印



# 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=Process(target=task,args=('alex',))           #元祖形式
#     t.start()
#     print('主进程')   #一定是先打印主进程  因为他要申请内存空间

将开启进程的信号发给操作系统后，操作系统要申请内存空间，让好拷贝父进程地址空间到子进程，开销远大于线程

#2同一进程内的多个线程共享进程的地址空间
'''
from multiprocessing import Process
import os
def work():
    global n
    n=0

if __name__ == '__main__':
    n=100
    p=Process(target=work)
    p.start()
    p.join()
    print('主',n)


from threading import Thread
import os
def work():
    global n
    n=0

if __name__ == '__main__':
    n=100
    t=Thread(target=work)
    t.start()
    t.join()
    print('主线程',n)
'''


#3 pid

# from multiprocessing import Process
# import os
#
# def work():
#     print('hello',os.getpid())
#
# if __name__ == '__main__':
#     p1=Process(target=work)
#     p2=Process(target=work)
#     p1.start()
#     p2.start()
#     print('主进程',os.getpid())


from threading import Thread
import os

def work():
    print('hello',os.getpid())

if __name__ == '__main__':
    t1=Thread(target=work)

    t1.start()
    print('主线程pid',os.getpid())