bug#65325: "make check" hangs on Cygwin

[Ken Brown <kbrown@cornell.edu>]

On 8/16/2023 1:49 PM, Ken Brown wrote:
> On 8/16/2023 11:23 AM, Ken Brown wrote:
>> On 8/16/2023 7:54 AM, Eli Zaretskii wrote:
>>>> From: Bruno Haible <bruno@clisp.org>
>>>> Date: Wed, 16 Aug 2023 00:08:08 +0200
>>>>
>>>> Building Emacs (git sources from today) on Cygwin 2.9.0/x86_64:
>>
>> This is a pretty old Cygwin release.
>>
>>>> 1. I configured in a subdirectory (VPATH build) with options
>>>>       --disable-silent-rules --without-all --without-x
>>>> 2. "make" succeeds.
>>>> 3. "make check" leads to a process that is stuck, does not continue
>>>>     for several hours. It does not eat much CPU time, but nevertheless,
>>>>     something is blocked. Log file 'make-check.log' is attached.
>>>
>>> Thanks.  Alas, the maintainer of Cygwin Emacs (CC'ed) has been silent
>>> for quite some time, so I'm not sure when and how this could be
>>> addressed.
>>
>> I'll test this using the current Cygwin release.
> 
> I can reproduce the hang.  But I don't get the hang in the default build 
> on my system (no configure options).  I'll have to play with the 
> configure options and try to figure out what's going on.

OK, the hang in server-tests.el [and a similar hang in 
keyboard-tests.el] occurs when getchar is called at keyboard.c:3978. 
This call only occurs if dbus, file notification, and threads are all 
disabled, i.e., if the configure options without-dbus, 
without-file-notification, and without-threads are all specified or 
implied.  I don't understand the keyboard code well enough to know (a) 
why we reach that call to getchar in the context of the hanging tests 
and (b) why getchar is only called in the absence of dbus, file 
notification, and threads.

I can work around the problem by always avoiding that getchar call on 
Cygwin (i.e., by adding "&& !defined CYGWIN" at line 3972).  With that 
change, all tests pass on Cygwin with Bruno's configure options.  But I 
don't want to make that change without understanding what's going on. 
Can anyone help?

Ken