Fix handling of pending signals in wait_reading_process_output (Bug#8869).

* process.c (wait_reading_process_output): Bypass select if
waiting for a cell while ignoring keyboard input, and input is
pending.  Suggested by Jan Djärv.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/process.c b/src/process.c
index c46437fe8cb..0fe7068af3b 100644
--- a/src/process.c
+++ b/src/process.c
@@ -4479,13 +4479,19 @@ wait_reading_process_output (int time_limit, int microsecs, int read_kbd,
             set_waiting_for_input (&timeout);
         }
 
+      /* Skip the `select' call if input is available and we're
+         waiting for keyboard input or a cell change (which can be
+         triggered by processing X events).  In the latter case, set
+         nfds to 1 to avoid breaking the loop.  */
       no_avail = 0;
-      if (read_kbd && detect_input_pending ())
+      if ((read_kbd || !NILP (wait_for_cell))
+          && detect_input_pending ())
         {
-          nfds = 0;
+          nfds = read_kbd ? 0 : 1;
           no_avail = 1;
         }
-      else
+
+      if (!no_avail)
         {
 
 #ifdef ADAPTIVE_READ_BUFFERING