Use a C based SIGCHLD handler

Running python code in signal handlers makes me nervous

kitty/data-types.c

@@ -9,6 +9,8 @@
 #include "modes.h"
 #include <stddef.h>
 #include <termios.h>
+#include <signal.h>
+#include <sys/wait.h>
 #ifdef WITH_PROFILER
 #include <gperftools/profiler.h>
 #endif
@@ -81,6 +83,28 @@ pyset_iutf8(PyObject UNUSED *self, PyObject *args) {
     Py_RETURN_NONE;
 }
 
+static void
+handle_sigchld(int UNUSED signum, siginfo_t *sinfo, void UNUSED *unused) {
+    if (sinfo->si_code != CLD_EXITED) return;
+    int sav_errno = errno, status;
+    while(true) {
+        if (waitpid(sinfo->si_pid, &status, WNOHANG) == -1) {
+            if (errno != EINTR) break;
+        } else break;
+    }
+    errno = sav_errno;
+}
+
+static PyObject*
+install_sigchld_handler(PyObject UNUSED *self) {
+    struct sigaction sa;
+    sa.sa_flags = SA_SIGINFO;
+    sa.sa_sigaction = handle_sigchld;
+    sigemptyset(&sa.sa_mask);
+    if (sigaction(SIGCHLD, &sa, NULL) == -1) return PyErr_SetFromErrno(PyExc_OSError);
+    Py_RETURN_NONE;
+}
+
 #ifdef WITH_PROFILER
 static PyObject*
 start_profiler(PyObject UNUSED *self, PyObject *args) {
@@ -105,6 +129,7 @@ static PyMethodDef module_methods[] = {
     {"redirect_std_streams", (PyCFunction)redirect_std_streams, METH_VARARGS, ""},
     {"wcwidth", (PyCFunction)wcwidth_wrap, METH_O, ""},
     {"change_wcwidth", (PyCFunction)change_wcwidth_wrap, METH_O, ""},
+    {"install_sigchld_handler", (PyCFunction)install_sigchld_handler, METH_NOARGS, ""},
 #ifdef WITH_PROFILER
     {"start_profiler", (PyCFunction)start_profiler, METH_VARARGS, ""},
     {"stop_profiler", (PyCFunction)stop_profiler, METH_NOARGS, ""},

kitty/main.py

@@ -3,7 +3,6 @@
 # License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 
 import argparse
-import errno
 import locale
 import os
 import signal
@@ -25,8 +24,8 @@ from .fast_data_types import (
     GLFW_OPENGL_FORWARD_COMPAT, GLFW_OPENGL_PROFILE, GLFW_SAMPLES,
     GLFW_STENCIL_BITS, GLFWWindow, change_wcwidth, check_for_extensions,
     clear_buffers, glewInit, glfw_init, glfw_init_hint_string,
-    glfw_swap_interval, glfw_terminate, glfw_window_hint, set_logical_dpi,
+    glfw_swap_interval, glfw_terminate, glfw_window_hint,
-    set_options
+    install_sigchld_handler, set_logical_dpi, set_options
 )
 from .layout import all_layouts
 from .utils import color_as_int, detach, get_logical_dpi, safe_print
@@ -245,19 +244,6 @@ def setup_profiling(args):
             print('To view the graphical call data, use: kcachegrind', cg)
 
 
-def reap_zombies(*a):
-    while True:
-        try:
-            pid, status = os.waitpid(-1, os.WNOHANG)
-            if pid == 0:
-                break
-        except OSError as err:
-            if err.errno != errno.EINTR:
-                break
-        except Exception:
-            break
-
-
 def main():
     try:
         sys.setswitchinterval(1000.0)  # we have only a single python thread
@@ -302,7 +288,7 @@ def main():
     try:
         with setup_profiling(args):
             # Avoid needing to launch threads to reap zombies
-            signal.signal(signal.SIGCHLD, reap_zombies)
+            install_sigchld_handler()
             run_app(opts, args)
             signal.signal(signal.SIGCHLD, signal.SIG_DFL)
     finally: