emacs-28 e848880: Avoid aborts when a thread is signaled while "waiting for input".

[Eli Zaretskii]

branch: emacs-28
commit e8488808dfe1460ce07042a1a523097ab90cf079
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Avoid aborts when a thread is signaled while "waiting for input".
    
    * src/process.c (kbd_is_ours): New function.
    (wait_reading_process_output): Set 'waiting_for_input' only if the
    current thread is monitoring the keyboard descriptor.  See also
    https://lists.gnu.org/archive/html/emacs-devel/2021-10/msg01180.html.
    (Bug#51229)
---
 src/process.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/process.c b/src/process.c
index 746cdc0..6731f88 100644
--- a/src/process.c
+++ b/src/process.c
@@ -683,6 +683,22 @@ clear_waiting_thread_info (void)
     }
 }
 
+/* Return TRUE if the keyboard descriptor is being monitored by the
+   current thread, FALSE otherwise.  */
+static bool
+kbd_is_ours (void)
+{
+  for (int fd = 0; fd <= max_desc; ++fd)
+    {
+      if (fd_callback_info[fd].waiting_thread != current_thread)
+       continue;
+      if ((fd_callback_info[fd].flags & (FOR_READ | KEYBOARD_FD))
+         == (FOR_READ | KEYBOARD_FD))
+       return true;
+    }
+  return false;
+}
+
 
 /* Compute the Lisp form of the process status, p->status, from
    the numeric status that was returned by `wait'.  */
@@ -5312,13 +5328,13 @@ wait_reading_process_output (intmax_t time_limit, int 
nsecs, int read_kbd,
               wait_reading_process_output_1 ();
         }
 
-      /* Cause C-g and alarm signals to take immediate action,
+      /* Cause C-g signals to take immediate action,
         and cause input available signals to zero out timeout.
 
         It is important that we do this before checking for process
         activity.  If we get a SIGCHLD after the explicit checks for
         process activity, timeout is the only way we will know.  */
-      if (read_kbd < 0)
+      if (read_kbd < 0 && kbd_is_ours ())
        set_waiting_for_input (&timeout);
 
       /* If status of something has changed, and no input is
@@ -5448,7 +5464,7 @@ wait_reading_process_output (intmax_t time_limit, int 
nsecs, int read_kbd,
        {
          clear_waiting_for_input ();
          redisplay_preserve_echo_area (11);
-         if (read_kbd < 0)
+         if (read_kbd < 0 && kbd_is_ours ())
            set_waiting_for_input (&timeout);
        }