> On Jun 3, 2020, at 07:13, Yuya Nishihara <y...@tcha.org> wrote:
>
> On Wed, 03 Jun 2020 05:46:05 +0200, Manuel Jacob wrote:
>> On 2020-06-03 00:04, Augie Fackler wrote:
>>>> On Jun 2, 2020, at 14:07, Manuel Jacob <m...@manueljacob.de> wrote:
>>>>
>>>> # HG changeset patch
>>>> # User Manuel Jacob <m...@manueljacob.de>
>>>> # Date 1591120869 -7200
>>>> # Tue Jun 02 20:01:09 2020 +0200
>>>> # Branch stable
>>>> # Node ID ebbc45544673c33ea3beb887ed4d5230b015102a
>>>> # Parent 91e509a12dbc4cd6cf2dcb9dae3ed383932132ac
>>>> py3: always flush ui streams on Python 3
>>>>
>>>> On Python 2, we rely on that stdout and stderr are line buffered.
>>>> Python 3’s
>>>> io module doesn’t offer line buffered binary streams.
>>>
>>> We use the underlying non-buffer thing though for std{err, out}
>>> though, or so I thought. Are you observing behavior that this
>>> corrects?
>>
>> pycompat says:
>>
>> stdout = sys.stdout.buffer
>> stderr = sys.stderr.buffer
>>
>> They are <_io.BufferedWriter name='<stdout>'> and <_io.BufferedWriter
>> name='<stderr>'>, respectively.
>>
>> I observed the error in TortoiseHg, which is a long-running process.
>>
>> To trigger the problem with the hg command, you would need to do
>> something slow that prints on `self._fout`, e.g. `hg pull
>> https://www.mercurial-scm.org/repo/hg --debug`.
>
> Denis, do you have any idea? My assumption was sys.stdout.buffer was magically
> line-buffered, but it appears not at least with Python 3.8.3 on Linux.
>
> https://www.mercurial-scm.org/repo/hg/rev/227ba1afcb65
>
>>>> --- a/mercurial/ui.py
>>>> +++ b/mercurial/ui.py
>>>> @@ -1198,9 +1198,14 @@ class ui(object):
>>>> label = opts.get('label', b'')
>>>> msg = self.label(msg, label)
>>>> dest.write(msg)
>>>> + # On Python 2, stdout and stderr are usually line
>>>> buffered, but
>>>> # stderr may be buffered under win32 when redirected to
>>>> files,
>>>> # including stdout.
>>>> - if dest is self._ferr and not getattr(self._ferr,
>>>> 'closed', False):
>>>> + # On Python 3, we use the underlying binary buffer, which
>>>> does not
>>>> + # support line buffering.
>>>> + if (pycompat.ispy3 or dest is self._ferr) and not
>>>> getattr(
>>>> + self._ferr, 'closed', False
>>>> + ):
>>>> dest.flush()
>
> Flushing stdout per write() sounds bad. If that's the only way to work
> around Py3 io module, we'll probably need to check if the stdout is
> a tty or not.
Agreed. Maybe we could sniff for a \n in the output stream, but I dunno if
that's likely to be a win.
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