Re: [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.y...@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