init: Request SCHED_RR using CAP_SYS_NICE and add Python to nix dev shell (#2690)

* nix: add python3 to devShell

* init: request SCHED_RR scheduling policy

* init: checks if host supports reseting scheduler on fork

* init: make gainRealTime more compatible with other OSes

* init: remove linux-only code

flake.nix

@@ -77,7 +77,7 @@
     devShells = genSystems (system: {
       default = pkgsFor.${system}.mkShell {
         name = "hyprland-shell";
-        nativeBuildInputs = with pkgsFor.${system}; [cmake];
+        nativeBuildInputs = with pkgsFor.${system}; [ cmake python3 ];
         buildInputs = [self.packages.${system}.wlroots-hyprland];
         inputsFrom = [
           self.packages.${system}.wlroots-hyprland

src/init/initHelpers.cpp

@@ -3,3 +3,19 @@
 bool Init::isSudo() {
     return getuid() != geteuid() || !geteuid();
 }
+
+void Init::gainRealTime() {
+    const int                minPrio = sched_get_priority_min(SCHED_RR);
+    const struct sched_param param   = {.sched_priority = minPrio};
+
+    if (pthread_setschedparam(pthread_self(), SCHED_RR, &param)) {
+        Debug::log(WARN, "Failed to change process scheduling strategy");
+        return;
+    }
+
+    pthread_atfork(NULL, NULL, []() {
+        const struct sched_param param = {.sched_priority = 0};
+        if (pthread_setschedparam(pthread_self(), SCHED_OTHER, &param))
+            Debug::log(WARN, "Failed to reset process scheduling strategy");
+    });
+}

src/init/initHelpers.hpp

@@ -4,4 +4,5 @@
 
 namespace Init {
     bool isSudo();
+    void gainRealTime();
 };

src/main.cpp

@@ -89,6 +89,7 @@ int main(int argc, char** argv) {
     }
 
     std::cout << "Welcome to Hyprland!\n";
+    Init::gainRealTime();
 
     // let's init the compositor.
     // it initializes basic Wayland stuff in the constructor.