Question

python 多进程是真的并发吗

Answer 1

Python提供了非常好用的多进程包multiprocessing，你只需要定义一个函数，Python会替你完成其他所有事情。
借助这个包，可以轻松完成从单进程到并发执行的转换。

1、新建单一进程
如果我们新建少量进程，可以如下：
import multiprocessing
import time

def func(msg):
for i in xrange(3):
print msg
time.sleep(1)

if __name__ == "__main__":
p = multiprocessing.Process(target=func, args=("hello", ))
p.start()
p.join()
print "Sub-process done."12345678910111213

2、使用进程池
是的，你没有看错，不是线程池。它可以让你跑满多核CPU，而且使用方法非常简单。
注意要用apply_async，如果落下async，就变成阻塞版本了。
processes=4是最多并发进程数量。
import multiprocessing
import time

def func(msg):
for i in xrange(3):
print msg
time.sleep(1)

if __name__ == "__main__":
pool = multiprocessing.Pool(processes=4)
for i in xrange(10):
msg = "hello %d" %(i)
pool.apply_async(func, (msg, ))
pool.close()
pool.join()
print "Sub-process(es) done."12345678910111213141516

3、使用Pool，并需要关注结果
更多的时候，我们不仅需要多进程执行，还需要关注每个进程的执行结果，如下：
import multiprocessing
import time

def func(msg):
for i in xrange(3):
print msg
time.sleep(1)
return "done " + msg

if __name__ == "__main__":
pool = multiprocessing.Pool(processes=4)
result = []
for i in xrange(10):
msg = "hello %d" %(i)
result.append(pool.apply_async(func, (msg, )))
pool.close()
pool.join()
for res in result:
print res.get()
print "Sub-process(es) done."1234567891011121314151617181920

2014.12.25更新
根据网友评论中的反馈，在Windows下运行有可能崩溃(开启了一大堆新窗口、进程)，可以通过如下调用来解决：
multiprocessing.freeze_support()1

附录（自己的脚本）：
#!/usr/bin/python
import threading
import subprocess
import datetime
import multiprocessing

def dd_test(round, th):
test_file_arg = 'of=/zbkc/test_mds_crash/1m_%s_%s_{}' %(round, th)
command = "seq 100 | xargs -i dd if=/dev/zero %s bs=1M count=1" %test_file_arg
print command
subprocess.call(command,shell=True,stdout=open('/dev/null','w'),stderr=subprocess.STDOUT)

def mds_stat(round):
p = subprocess.Popen("zbkc mds stat", shell = True, stdout = subprocess.PIPE)
out = p.stdout.readlines()
if out[0].find('active') != -1:
command = "echo '0205pm %s round mds status OK, %s' >> /round_record" %(round, datetime.datetime.now())
command_2 = "time (ls /zbkc/test_mds_crash/) 2>>/round_record"
command_3 = "ls /zbkc/test_mds_crash | wc -l >> /round_record"
subprocess.call(command,shell=True)
subprocess.call(command_2,shell=True)
subprocess.call(command_3,shell=True)
return 1
else:
command = "echo '0205 %s round mds status abnormal, %s, %s' >> /round_record" %(round, out[0], datetime.datetime.now())
subprocess.call(command,shell=True)
return 0

#threads = []
for round in range(1, 1600):
pool = multiprocessing.Pool(processes = 10) #使用进程池
for th in range(10):
# th_name = "thread-" + str(th)
# threads.append(th_name) #添加线程到线程列表
# threading.Thread(target = dd_test, args = (round, th), name = th_name).start() #创建多线程任务
pool.apply_async(dd_test, (round, th))
pool.close()
pool.join()
#等待线程完成
# for t in threads:
# t.join()

if mds_stat(round) == 0:
subprocess.call("zbkc -s",shell=True)
break