Report failures to write to child

kitty/child-monitor.c

@@ -221,10 +221,11 @@ needs_write(ChildMonitor *self, PyObject *args) {
     unsigned long id, sz;
     const char *data;
     if (!PyArg_ParseTuple(args, "ks#", &id, &data, &sz)) return NULL; 
-    if (!sz) { Py_RETURN_NONE; }
+    PyObject *found = Py_False;
     children_mutex(lock);
     for (size_t i = 0; i < self->count; i++) {
         if (children[i].id == id) { 
+            found = Py_True;
             Screen *screen = children[i].screen;
             screen_mutex(lock, write);
             uint8_t *buf = PyMem_RawRealloc(screen->write_buf, screen->write_buf_sz + sz);
@@ -240,7 +241,8 @@ needs_write(ChildMonitor *self, PyObject *args) {
     }
     children_mutex(unlock);
     if (PyErr_Occurred()) return NULL;
-    Py_RETURN_NONE;
+    Py_INCREF(found);
+    return found;
 }
 
 static PyObject *

kitty/window.py

@@ -2,10 +2,11 @@
 # vim:fileencoding=utf-8
 # License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 
+import sys
 import weakref
 from collections import deque
-from time import monotonic
 from itertools import count
+from time import monotonic
 
 from .char_grid import CharGrid, DynamicColor
 from .constants import (
@@ -112,8 +113,10 @@ class Window:
 
     def write_to_child(self, data):
         if data:
-            get_boss().child_monitor.needs_write(self.id, data)
-            wakeup()
+            if get_boss().child_monitor.needs_write(self.id, data) is True:
+                wakeup()
+            else:
+                print('Failed to write to child %d as it does not exist' % self.id, file=sys.stderr)
 
     def bell(self):
         if self.opts.enable_audio_bell: