[PATCH v2 3/3] Cygwin: pty: Fixup pty state after a cygwin app exits

[Mark Geisert]

Hi Takashi,

All of your corrections and additions LGTM.  This one can be pushed.
Thanks,

..mark

On 6/23/2026 6:31 AM, Takashi Yano wrote:
> Hi Mark,
> 
> Thanks for reviewing.
> 
> On Tue, 23 Jun 2026 01:07:16 -0700
> Mark Geisert  wrote:
>> Hi Takashi,
>>
>> On 6/13/2026 7:09 AM, Takashi Yano wrote:
>>> Previously, the cygwin process on pty is always a child of another
>>> cygwin app on pty. If a cygwin app is a child of non-cygwin app
>>> in pseudo console, it was running on console originating from
>>> pseudo console. Now, the child of a non-cygwin app on pseudo console
>>> is running on pty, so, it is necessary to restore the pty state
>>> to the state where the parent process is running. This patch
>>> does the following fixup:
>>>    1) Switch pipe mode to cyg-pipe to nat-pipe.
>>                           ^^^^^^^^^^^^^^^^^^^^^^^ this can't be correct
> 
> Auch! "from cyg-pipe to nat-pipe"
>>
>>>    2) Notify the current cursor position to pseudo console
>>>
>>> These prevent the problems:
>>>    1) Run 'cat' in cmd.exe and stop it by Ctrl-C. After that
>>>       cmd.exe cannot receive key input.
>>>    2) Run 'ps' in cmd.exe. The cursor position will not be
>>>       maintained correctly after that.
>>>
>>> Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
>>> Reviewed-by:
>>> ---
>>>    winsup/cygwin/fhandler/pty.cc           | 73 ++++++++++++++++++++++++-
>>>    winsup/cygwin/local_includes/fhandler.h |  2 +
>>>    winsup/cygwin/local_includes/tty.h      |  1 +
>>>    3 files changed, 73 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/winsup/cygwin/fhandler/pty.cc b/winsup/cygwin/fhandler/pty.cc
>>> index b3a8d57cc..f4473bb69 100644
>>> --- a/winsup/cygwin/fhandler/pty.cc
>>> +++ b/winsup/cygwin/fhandler/pty.cc
>>> @@ -388,6 +388,52 @@ atexit_func (void)
>>>        }
>>>    }
>>>    
>>> +void
>>> +fhandler_pty_slave::req_fixup_pcon_state (void)
>>> +{
>>> +  while (true)
>>> +    {
>>> +      WaitForSingleObject (input_mutex, mutex_timeout);
>>> +      if (!get_ttyp ()->pcon_start_pid)
>>> +	break;
>>> +      /* Another request is on going. */
>>> +      ReleaseMutex (input_mutex);
>>> +      yield ();
>>> +    }
>>> +
>>> +  DWORD n;
>>> +  /* indicates that this "ESC[6n" is just for fixing-up corsor position */
>>                                                              ^^^^^^ typo here
> 
> Fixed.
> 
>>> +  get_ttyp ()->req_fixup_pcon_cur_pos = true;
>>> +  get_ttyp ()->req_xfer_input = true; /* indicates that this "ESC[6n"
>>> +					 is just for transfer input */
>>> +  get_ttyp ()->pcon_start = true;
>>> +  get_ttyp ()->pcon_start_pid = myself->pid;
>>> +  WriteFile (get_output_handle (), "\033[6n", 4, &n, NULL);
>>> +  ReleaseMutex (input_mutex);
>>> +  while (get_ttyp ()->pcon_start_pid)
>>> +    /* wait for completion of fixing-up in master::write(). */
>>> +    yield ();
>>> +}
>>> +
>>> +void
>>> +fhandler_pty_master::fixup_pcon_cursor_position (int x, int y)
>>> +{
>>> +  HANDLE pcon_owner = OpenProcess (PROCESS_DUP_HANDLE, FALSE,
>>> +				   get_ttyp ()->nat_pipe_owner_pid);
>>> +  HANDLE h_pcon_out = NULL;
>>> +  DuplicateHandle (pcon_owner, get_ttyp ()->h_pcon_out,
>>> +		   GetCurrentProcess (), &h_pcon_out,
>>> +		   0, TRUE, DUPLICATE_SAME_ACCESS);
>>> +  CloseHandle (pcon_owner);
>>> +  DWORD target_pid = get_ttyp ()->nat_pipe_owner_pid;
>>> +  DWORD resume_pid =
>>> +    fhandler_pty_common::attach_console_temporarily (target_pid);
>>> +  COORD cur_pos = {(SHORT) (x - 1), (SHORT) (y - 1)};
>>> +  SetConsoleCursorPosition (h_pcon_out, cur_pos);
>>> +  fhandler_pty_common::resume_from_temporarily_attach (resume_pid);
>>> +  CloseHandle (h_pcon_out);
>>> +}
>>> +
>>>    #define DEF_HOOK(name) static __typeof__ (name) *name##_Orig
>>>    /* CreateProcess() is hooked for GDB etc. */
>>>    DEF_HOOK (CreateProcessA);
>>> @@ -1162,6 +1208,19 @@ err_no_msg:
>>>    bool
>>>    fhandler_pty_slave::open_setup (int flags)
>>>    {
>>> +  if (get_ttyp ()->pcon_activated)
>>> +    {
>>> +      HANDLE pcon_owner = OpenProcess (PROCESS_DUP_HANDLE, FALSE,
>>> +				       get_ttyp ()->nat_pipe_owner_pid);
>>> +      DuplicateHandle (pcon_owner, get_ttyp ()->h_pcon_in,
>>> +		       GetCurrentProcess (), &get_handle_nat (),
>>> +		       0, TRUE, DUPLICATE_SAME_ACCESS);
>>> +      DuplicateHandle (pcon_owner, get_ttyp ()->h_pcon_out,
>>> +		       GetCurrentProcess (), &get_output_handle_nat (),
>>> +		       0, TRUE, DUPLICATE_SAME_ACCESS);
>>> +      CloseHandle (pcon_owner);
>>> +    }
>>> +
>>>      set_flags ((flags & ~O_TEXT) | O_BINARY);
>>>      myself->set_ctty (this, flags);
>>>      report_tty_counts (this, "opened", "");
>>> @@ -1171,6 +1230,9 @@ fhandler_pty_slave::open_setup (int flags)
>>>    void
>>>    fhandler_pty_slave::cleanup ()
>>>    {
>>> +  if (get_ttyp ()->pcon_activated && get_ttyp ()->getpgid () == myself->pgid)
>>> +    req_fixup_pcon_state ();
>>> +
>>>      /* This used to always call fhandler_pty_common::close when we were execing
>>>         but that caused multiple closes of the handles associated with this pty.
>>>         Since close_all_files is not called until after the cygwin process has
>>> @@ -2478,7 +2540,14 @@ fhandler_pty_master::write (const void *ptr, size_t len)
>>>    	      /* req_xfer_input is true if "ESC[6n" was sent just for
>>>    		 triggering transfer_input() in master. In this case,
>>>    		 the response sequence should not be written. */
>>
>> The above comment describes the req_xfer case, but says nothing about
>> the the req_fixup_pcon_cur_pos case now inserted before it.
> 
> I'll modify the comment above like:
>        /* req_fixup_pcon_cur_pos is true if "ESC[6n" was sent
>           for requesting cursor-position-fixup that is needed
>           when a non-cygwin app executes a cygwin app and the
>           cygwin app exits.
>           req_xfer_input is true if "ESC[6n" was sent just for
>           triggering transfer_input() in master. In this case,
>           the response sequence should not be written. */
> 
> Does this look OK to you?

That's great!

..mark