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Date: Tue, 19 Aug 2014 22:38:17 +0530
Subject: Re: asyncio subprocess PIPE output lost
From: Kushal Kumaran <kushal@locationd.net>
To: python-list@python.org
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On Tue, Aug 19, 2014 at 1:09 PM, yuzhichang <yuzhichang@gmail.com> wrote:
> Hi all,
>     I'm new to asyncio introduced by Python 3.4. I created two tasks each pings a host. I noticed some pieces of output will be lost(see "error: found icmp_seq gap"). If I changed to run only one task, this problem never occur.
>     Do you have any idea?
>     Thanks!
> Zhichang
>
> zhichyu@cto-team-6:~$ python3 asyn2.py
> got line: b'PING tyr.global.tektronix.net (10.250.163.252) 56(84) bytes of data.\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=2 ttl=55 time=204 ms\n'
> got line: b'PING babylon.rich.tek.com (10.250.155.123) 56(84) bytes of data.\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=2 ttl=55 time=205 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=3 ttl=55 time=205 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=3 ttl=55 time=205 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=4 ttl=55 time=196 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=4 ttl=55 time=198 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=5 ttl=55 time=181 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=5 ttl=55 time=182 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=6 ttl=55 time=180 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=6 ttl=55 time=179 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=7 ttl=55 time=193 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=7 ttl=55 time=196 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=8 ttl=55 time=185 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=8 ttl=55 time=187 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=9 ttl=55 time=213 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=9 ttl=55 time=211 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=10 ttl=55 time=192 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=10 ttl=55 time=192 ms\n'
> got line: b'64 bytes from tyr.global.tektronix.net (10.250.163.252): icmp_seq=11 ttl=55 time=210 ms\n'
> got line: b'64 bytes from babylon.rich.tek.com (10.250.155.123): icmp_seq=12 ttl=55 time=210 ms\n'
> error: found icmp_seq gap!
>
> <snipped code>

Before looking for possible bugs in your code, the first thing to
check would be if you are actually missing ping replies, rather than
output from the ping command.  Try increasing the timeout (-W) for the
ping command.  If you're familiar with tools like tcpdump and
wireshark, you could use those to examine the network traffic and see
if replies are missing.

-- 
regards,
kushal