Python基础之九进程和线程

import os
print('Process (%s) start...' % os.getpid())
pid = os.fork()
if pid == 0:
print('I an child process (%s) and my parent is %s' % (os.getpid(), os.getpid()))
else:
print('I (%s) just created a child process (%s).' % (os.getpid(), pid))

'''
multiprocessing
'''
from multiprocessing import Process
import os

def run_proc(name):
print(('Run child process %s (%s)...' % (name, os.getpid())))

if __name__ == '__main__':
print('Parent process %s.' % os.getpid())
#创建子进程时,只需要传入一个执行函数和函数的参数,创建一个Process实例,用start()方法启动,这样比fork()简单
p = Process(target=run_proc, args=('test',))
print('Child process will start')
p.start()#启动进程
p.join()#等待子进程结束后再继续往下运行,通常用于进程间的通病
print('Child process end.')
'''
Pool
如果需要启动大量子进程,可以用进程池的方式批量创建子进程
'''

from multiprocessing import Pool
import os, time, random

def long_time_task(name):
print('Run task %s (%s)...' % (name, os.getpid()))
start = time.time()
time.sleep(random.random() * 3)
end = time.time()
print('Task %s runs %0.2f seconds.' % (name, (end - start)))

if __name__ == '__main__':
print('Parent process %s.' % os.getpid())
p = Pool(4)
for i in range(5):
p.apply_async(long_time_task, args=(i, ))
print('Wating for all subprocesses done...')
p.close()
p.join()
print('All subprocesses done.')

'''
子进程
'''
import subprocess
print('$ nslookup www.python.org')
r = subprocess.call(['nslookup', 'www.python.org'])
print('Exit code:', r)

'''
进程间通信
'''
from multiprocessing import Process, Queue
import os, time, random

#写进程执行代码
def write(q):
print('Process to write: %s' % os.getpid())
for value in ['A', 'B', 'C']:
print('Put %s to queue...' % value)
q.put(value)
time.sleep(random.random())

#读进程执行的代码
def read(q):
print('Process to read: %s' % os.getpid())
while True:
value = q.get(True)
print('Get %s from queue.' % value)

if __name__ == '__main__':
#父进程创建Queue,并传递给各个子进程
q = Queue()
pw = Process(target=write, args= (q,))
pr = Process(target=read, args= (q,))
#启动子进程pw,写入
pw.start()
#启动子进程pr,读取
pr.start()
#等待pw结束
pw.join()
#pr进程里面是死循环,无法等待其结束,只能强制执行
pr.terminate()

'''
多线程
多任务可以有多个进程完成, 也可以由一个进程内的多线程完成
'''

import time, threading

print('>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>以下是多线程执行代码')
#新线程执行的代码
def loop():
print('thread %s is runing...' % threading.current_thread().name)
n = 0
while n < 5:
n = n + 1
print('thread %s >>> %s' % (threading.current_thread().name, n))
time.sleep(1)
print('thread %s ended.' % threading.current_thread().name)

print('thread %s is runing...' % threading.current_thread().name)
t = threading.Thread(target=loop, name='LoopThread')
t.start()
t.join()
print('thread %s ended.' % threading.current_thread().name)

'''
Lock
多线程和多进程最大的不同在于,多进程中,同一个变量各自有一份拷贝存在于每个进程中,互不影响,
而多线程中,所有变量都由所有线程共享,所有,任何一个变量都可以被任何一个线程修改,
因此,线程之间共享数据最大危险在于多个线程同时修改一个变量

'''
blance = 0
lock = threading.Lock()

def run_thread(n):
for i in range(100000):
#现获取锁
lock.acquire()
try:
pass
#修改something
finally:
pass
#改完释放锁

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