Reap zombies in a signal handler

Avoids relying on jernel behavior, which may not be portable across all
unices

kitty/main.py

@@ -244,6 +244,14 @@ def setup_profiling(args):
             print('To view the graphical call data, use: kcachegrind', cg)
 
 
+def reap_zombies(*a):
+    while True:
+        try:
+            os.waitpid(-1, os.WNOHANG)
+        except OSError:
+            break
+
+
 def main():
     try:
         sys.setswitchinterval(1000.0)  # we have only a single python thread
@@ -287,8 +295,8 @@ def main():
         raise SystemExit('GLFW initialization failed')
     try:
         with setup_profiling(args):
-            # Let the kernel take care of reaping zombie child processes
+            # Avoid needing to launch threads to reap zombies
-            signal.signal(signal.SIGCHLD, signal.SIG_IGN)
+            signal.signal(signal.SIGCHLD, reap_zombies)
             run_app(opts, args)
             signal.signal(signal.SIGCHLD, signal.SIG_DFL)
     finally:

kitty/utils.py

@@ -165,7 +165,7 @@ def get_primary_selection():
         return ''  # There is no primary selection on OS X
     g = selection_clipboard_funcs()[0]
     if g is None:
-        # We cannot use check_output as we set SIGCHLD to SIG_IGN
+        # We cannot use check_output as we set a SIGCHLD handler to reap zombies
         ans = subprocess.Popen(['xsel', '-p'], stderr=subprocess.DEVNULL, stdin=subprocess.DEVNULL, stdout=subprocess.PIPE).stdout.read().decode('utf-8')
         if ans:
             # Without this for some reason repeated pastes dont work