小智..

6

写入后，进程将数据写入不同管道的顺序将丢失。

您无法判断在stderr之前是否已写入stdout。

您可以尝试在数据可用时以非阻塞方式同时从多个文件描述符中同时读取数据，但这只会最大程度地降低顺序不正确的可能性。

该程序应证明这一点：

#!/usr/bin/env python

# -*- coding: utf-8 -*-

import os

import select

import subprocess

testapps={

'slow': '''

import os

import time

os.write(1, 'aaa')

time.sleep(0.01)

os.write(2, 'bbb')

time.sleep(0.01)

os.write(1, 'ccc')

''',

'fast': '''

import os

os.write(1, 'aaa')

os.write(2, 'bbb')

os.write(1, 'ccc')

''',

'fast2': '''

import os

os.write(1, 'aaa')

os.write(2, 'bbbbbbbbbbbbbbb')

os.write(1, 'ccc')

'''

}

def readfds(fds, maxread):

while True:

fdsin, _, _ = select.select(fds,[],[])

for fd in fdsin:

s = os.read(fd, maxread)

if len(s) == 0:

fds.remove(fd)

continue

yield fd, s

if fds == []:

break

def readfromapp(app, rounds=10, maxread=1024):

f=open('testapp.py', 'w')

f.write(testapps[app])

f.close()

results={}

for i in range(0, rounds):

p = subprocess.Popen(['python', 'testapp.py'], stdout=subprocess.PIPE

, stderr=subprocess.PIPE)

data=''

for (fd, s) in readfds([p.stdout.fileno(), p.stderr.fileno()], maxread):

data = data + s

results[data] = results[data] + 1 if data in results else 1

print 'running %i rounds %s with maxread=%i' % (rounds, app, maxread)

results = sorted(results.items(), key=lambda (k,v): k, reverse=False)

for data, count in results:

print '%03i x %s' % (count, data)

print

print "=> if output is produced slowly this should work as whished"

print " and should return: aaabbbccc"

readfromapp('slow', rounds=100, maxread=1024)

print

print "=> now mostly aaacccbbb is returnd, not as it should be"

readfromapp('fast', rounds=100, maxread=1024)

print

print "=> you could try to read data one by one, and return"

print " e.g. a whole line only when LF is read"

print " (b's should be finished before c's)"

readfromapp('fast', rounds=100, maxread=1)

print

print "=> but even this won't work ..."

readfromapp('fast2', rounds=100, maxread=1)

并输出如下内容：

=> if output is produced slowly this should work as whished

and should return: aaabbbccc

running 100 rounds slow with maxread=1024

100 x aaabbbccc

=> now mostly aaacccbbb is returnd, not as it should be

running 100 rounds fast with maxread=1024

006 x aaabbbccc

094 x aaacccbbb

=> you could try to read data one by one, and return

e.g. a whole line only when LF is read

(b's should be finished before c's)

running 100 rounds fast with maxread=1

003 x aaabbbccc

003 x aababcbcc

094 x abababccc

=> but even this won't work ...

running 100 rounds fast2 with maxread=1

003 x aaabbbbbbbbbbbbbbbccc

001 x aaacbcbcbbbbbbbbbbbbb

008 x aababcbcbcbbbbbbbbbbb

088 x abababcbcbcbbbbbbbbbb