bug#70415: 30.0.50; [Cygwin] `lock-file' creates a symlink with funny name

[Ken Brown <kbrown@cornell.edu>]

On 5/4/2024 1:26 PM, Eli Zaretskii wrote:
>> Date: Sat, 4 May 2024 13:15:19 -0400
>> From: Ken Brown <kbrown@cornell.edu>
>> Cc: yamaoka@jpl.org, 70415@debbugs.gnu.org
>>
>> On 5/2/2024 10:26 AM, Ken Brown wrote:
>>> On 5/2/2024 2:21 AM, Eli Zaretskii wrote:
>>>>> Date: Wed, 1 May 2024 17:20:20 -0400
>>>>> Cc: yamaoka@jpl.org, 70415@debbugs.gnu.org
>>>>> From: Ken Brown <kbrown@cornell.edu>
>>>>>
>>>>>>        char const *lock_info_fmt = (boot
>>>>>>                   ? "%s@%s.%"PRIdMAX":%"PRIdMAX
>>>>>>                   : "%s@%s.%"PRIdMAX);
>>>>>>        int len = snprintf (lock_info_str, sizeof lock_info_str,
>>>>>>              lock_info_fmt, user_name, host_name, pid, boot);
>>>>>>
>>>>>> get_boot_sec calls get_boot_time, which is a Gnulib function (see
>>>>>> lib/boot-time.c).  So I guess the key to unlock this puzzle is
>>>>>> somewhere there.
>>>>>
>>>>> I took a quick look at get_boot_time and found a bug, which may explain
>>>>> why some Cygwin systems behave differently from others.  I've reported
>>>>> it here:
>>>>>
>>>>>      https://lists.gnu.org/archive/html/bug-gnulib/2024-05/msg00008.html
>>>>
>>>> Thanks.  This probably explains why the ":-NNNN" part sometimes
>>>> appears and sometimes doesn't appear in Cygwin builds of Emacs, but
>>>> AFAIU it does NOT explain why unlinking the symlink (when the file is
>>>> unlocked) fails when the lock file name includes the ":-NNNN" part.
>>>> Right?
>>>
>>> Yes, that's right.  I still need to look into that.
>>
>> It turns out that there was a Cygwin bug (already fixed in the Cygwin
>> development sources) that affected only version 3.5.3, and Bruno added a
>> workaround to Gnulib.  I now see the ":NNNN" part on my system, without
>> a minus sign, and the lock file is deleted properly.
> 
> Would you mind explaining for posterity (and for my personal
> curiosity) how what Bruno changed affects the deletion of the lock
> file?  Is that because the ":-NNNN" suffix had the dash (because the
> system's page file was deemed to eb a directory)?  If so, how did the
> presence of the dash cause the failure to delete the file?

Not only was the system's page file deemed to be a directory, but it was 
deemed to have a negative modification time.  I think that's where the 
dash came from.  But I don't know why that prevented the lock file from 
being deleted.  I fully expected to have to debug that problem after 
applying Bruno's patches, and it seemed like a miracle that I didn't 
have to.  I might still have to debug further if Katsumi reports that 
the problem isn't fixed for him.

Ken