[PATCH] Cygwin: pty: Do not transfer input to nat-pipe while masked

On the command "cat | non-cygwin-app", `cat` sometimes fails to read
key input. This happens when `cat` starts to read input before `non-
cygwin-app` configures pseudo console. This is because pipe state is
switched to nat-pipe when pseudo console is configured.

This patch prevent the pipe state from changing to nat-pipe state if
some cygwin process is reading input from the cyg-pipe.

Fixes: f20641789427 ("Cygwin: pty: Reduce unecessary input transfer.")
Signed-off-by: Takashi Yano <[email protected]>
Reviewed-by:
---
 winsup/cygwin/fhandler/pty.cc | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/winsup/cygwin/fhandler/pty.cc b/winsup/cygwin/fhandler/pty.cc
index 35e320507..b9e25519d 100644
--- a/winsup/cygwin/fhandler/pty.cc
+++ b/winsup/cygwin/fhandler/pty.cc
@@ -4401,6 +4401,18 @@ fhandler_pty_slave::transfer_input (tty::xfer_dir dir, HANDLE from, tty *ttyp,
 				    HANDLE input_available_event,
 				    HANDLE input_transferred_to_cyg)
 {
+  if (dir == tty::to_nat)
+    {
+      char name[MAX_PATH];
+      shared_name (name, TTY_SLAVE_READING, ttyp->get_minor ());
+      HANDLE masked = OpenEvent (READ_CONTROL, FALSE, name);
+      CloseHandle (masked);
+      if (masked)
+	/* Cygwin process is reading cyg-pipe.
+	   Do not transfer input to nat-pipe. */
+	return;
+    }
+
   HANDLE to;
   if (dir == tty::to_nat)
     to = ttyp->to_slave_nat ();
-- 
2.51.0