Make sure sleep-for always delays for as long as it's told

* src/dispnew.c (Fsleep_for): Call wait_reading_process_output in
a loop, to ensure we always wait exactly the required amount of
time.  (Bug#15990)

1 files changed, 10 insertions, 2 deletions

diff --git a/src/dispnew.c b/src/dispnew.c
index 1fc3cfeef44..7833fe3d01c 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -5679,8 +5679,16 @@ additional wait period, in milliseconds; this is for backwards compatibility.
   if (duration > 0)
     {
       struct timespec t = dtotimespec (duration);
-      wait_reading_process_output (min (t.tv_sec, WAIT_READING_MAX),
-                                   t.tv_nsec, 0, 0, Qnil, NULL, 0);
+      struct timespec tend = timespec_add (current_timespec (), t);
+
+      /* wait_reading_process_output returns as soon as it detects
+         output from any subprocess, so we wait in a loop until the
+         time expires.  */
+      do {
+        wait_reading_process_output (min (t.tv_sec, WAIT_READING_MAX),
+                                     t.tv_nsec, 0, 0, Qnil, NULL, 0);
+        t = timespec_sub (tend, current_timespec ());
+      } while (timespec_sign (t) > 0);
     }
 
   return Qnil;