python popen 标准输出卡住

Question

我已经阅读了许多涉及实时标准输出打印的问题，包括 J.F. Sebastian's Python 3 solution 的回答阅读标准输出。

然而，虽然他的解决方案适用于这种情况:

with Popen(['ping'] + ['169.254.79.191'] + ['-c'] + ['5'], stdout=PIPE, bufsize=1, universal_newlines=True) as p:
    for line in p.stdout:
        print(line, end='')

它无法像我预期的那样在我实际想要使用的应用程序中运行:

with Popen(['iperf3', '-c', '169.254.79.191', 'b', '100000000', '-p', '5202', 't', '5', '-R', '-V', '-u'], stdout=PIPE, bufsize=1, universal_newlines=True) as p:
     for line in p.stdout:
         print(line, end='')

对于 ping 场景，每一行都被打印出来，就像我手动运行它一样。使用 iperf，它会在两行输出后停止，并在应用程序完成时刷新所有内容。如果我在脚本中依次执行它们，我会得到以下输出:

pi@raspberrypi2:~/project $ python3.4 stdout_RT_test.py
PING 169.254.79.191 (169.254.79.191) 56(84) bytes of data.
64 bytes from 169.254.79.191: icmp_seq=1 ttl=64 time=0.854 ms
64 bytes from 169.254.79.191: icmp_seq=2 ttl=64 time=0.867 ms
64 bytes from 169.254.79.191: icmp_seq=3 ttl=64 time=0.877 ms
64 bytes from 169.254.79.191: icmp_seq=4 ttl=64 time=0.842 ms
64 bytes from 169.254.79.191: icmp_seq=5 ttl=64 time=0.834 ms

--- 169.254.79.191 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 3998ms
rtt min/avg/max/mdev = 0.834/0.854/0.877/0.040 ms
iperf 3.0.7
Linux raspberrypi2 4.4.50-v7+ #970 SMP Mon Feb 20 19:18:29 GMT 2017 armv7l GNU/Linux

IPERF 完成后显示此行之后的所有内容

Time: Wed, 29 Mar 2017 14:46:48 GMT
Connecting to host 169.254.79.191, port 5202
Reverse mode, remote host 169.254.79.191 is sending
      Cookie: raspberrypi2.1490798808.947399.0490a
[  4] local 169.254.181.167 port 41415 connected to 169.254.79.191 port 5202
Starting Test: protocol: UDP, 1 streams, 8192 byte blocks, omitting 0 seconds, 10 second test
[ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
[  4]   0.00-1.00   sec   136 KBytes  1.11 Mbits/sec  1.907 ms  0/17 (0%)
[  4]   1.00-2.00   sec   128 KBytes  1.05 Mbits/sec  0.966 ms  0/16 (0%)
[  4]   2.00-3.00   sec   128 KBytes  1.05 Mbits/sec  0.634 ms  0/16 (0%)
[  4]   3.00-4.00   sec   128 KBytes  1.05 Mbits/sec  0.522 ms  0/16 (0%)
[  4]   4.00-5.00   sec   128 KBytes  1.05 Mbits/sec  0.466 ms  0/16 (0%)
[  4]   5.00-6.00   sec   128 KBytes  1.05 Mbits/sec  0.456 ms  0/16 (0%)
[  4]   6.00-7.00   sec   128 KBytes  1.05 Mbits/sec  0.452 ms  0/16 (0%)
[  4]   7.00-8.00   sec   128 KBytes  1.05 Mbits/sec  0.447 ms  0/16 (0%)
[  4]   8.00-9.00   sec   128 KBytes  1.05 Mbits/sec  0.451 ms  0/16 (0%)
[  4]   9.00-10.00  sec   128 KBytes  1.05 Mbits/sec  0.460 ms  0/16 (0%)
- - - - - - - - - - - - - - - - - - - - - - - - -
Test Complete. Summary Results:
[ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
[  4]   0.00-10.00  sec  1.26 MBytes  1.06 Mbits/sec  0.460 ms  0/161 (0%)
[  4] Sent 161 datagrams
CPU Utilization: local/receiver 0.5% (0.0%u/0.5%s), remote/sender 0.0% (0.0%u/0.0%s)

iperf Done.

如在“间隔”列中所见，如果我手动运行相同的命令，大约每秒打印一行。我是 python 的新手，所以任何错误都是可能的。我尝试了其他几种缓存标准输出的方法，但它们也会像这样卡住输出。这能以某种方式解决吗？

BR安德烈亚斯

编辑:我认为问题是 iperf 没有刷新，但由于它显然每秒都在写一个新行，所以必须有一种方法可以在刷新之前捕获它。当运行更长的测试时，我注意到 stdout 缓冲区最终会达到最大值并且会刷新许多行并继续直到它再次满。

Answer 1

尝试将 --forceflush 命令行标志添加到 iperf3。这会导致 iperf3 在每行输出后刷新其输出。