exec: Spawn processes as direct children (#11735)

* exec: Spawn processes as direct children

Spawn processes as children rather than grandchildren.
This way, spawned processes may track Hyprland's state
by watching their parent, either directly or indirectly
(e.g., Linux's `PR_SET_PDEATH_SIG`).

Fixes #11728

* tests/exec: Add the test on process spawning

Add a test that ensures that:
- A spawned process remains a direct child of Hyprland;
- Upon termination, the process does not become a zombie.

src/main.cpp

@@ -5,6 +5,7 @@
 #include "init/initHelpers.hpp"
 #include "debug/HyprCtl.hpp"
 
+#include <csignal>
 #include <cstdio>
 #include <hyprutils/string/String.hpp>
 #include <hyprutils/memory/Casts.hpp>
@@ -35,6 +36,17 @@ static void help() {
     --version           -v       - Print this binary's version)");
 }
 
+static void reapZombieChildrenAutomatically() {
+    struct sigaction act;
+    act.sa_handler = SIG_DFL;
+    sigemptyset(&act.sa_mask);
+    act.sa_flags = SA_NOCLDWAIT;
+#ifdef SA_RESTORER
+    act.sa_restorer = NULL;
+#endif
+    sigaction(SIGCHLD, &act, nullptr);
+}
+
 int main(int argc, char** argv) {
 
     if (!getenv("XDG_RUNTIME_DIR"))
@@ -183,6 +195,8 @@ int main(int argc, char** argv) {
     if (!envEnabled("HYPRLAND_NO_RT"))
         NInit::gainRealTime();
 
+    reapZombieChildrenAutomatically();
+
     Debug::log(LOG, "Hyprland init finished.");
 
     // If all's good to go, start.