Re: [PATCH v3] iotests: Test NBD client reconnection

[Andrey Shinkevich]

On 08/11/2019 17:05, Roman Kagan wrote:
> On Fri, Nov 08, 2019 at 01:49:50PM +0000, Vladimir Sementsov-Ogievskiy wrote:
>> 01.11.2019 19:54, Andrey Shinkevich wrote:
>>> +def check_proc_NBD(proc, connector):
>>> +    try:
>>> +        exitcode = proc.wait(timeout=10)
>>> +
>>> +        if exitcode < 0:
>>> +            log('NBD {}: EXIT SIGNAL {}\n'.format(connector, -exitcode))
>>> +            log(proc.communicate()[0])
>>> +        else:
>>> +            line = proc.stdout.readline()
>>
>>
>> could we use proc.communicate() for both cases, what is the difference?
> 
> In fact if proc produces any non-trivial amount of output you are better
> off using .communicate() otherwise your child may block on output and
> never exit.  See
> https://docs.python.org/3/library/subprocess.html#subprocess.Popen.communicate
> for how to express the above logic correctly.  The exit code *after*
> .communicate is available in .returncode.
> 

The pattern by the link above does not work (Python3):

proc = subprocess.Popen(...)
try:
     outs, errs = proc.communicate(timeout=15)
except TimeoutExpired:
     proc.kill()
     outs, errs = proc.communicate()

as 'proc' cannot be used for output after being killed. It results in 
another exception being raised.

Andrey

>>
>>> +            log('NBD {}: {}'.format(connector, line.rstrip()))
>>> +
>>> +    except subprocess.TimeoutExpired:
>>> +        proc.kill()
>>> +        log('NBD {}: ERROR timeout expired'.format(connector))
>>> +    finally:
>>> +        if connector == 'server':
>>> +            os.remove(nbd_sock)
>>> +            os.remove(conf_file)
> 
> Roman.
> 

-- 
With the best regards,
Andrey Shinkevich