Improve thread safety

src/departure.zig

@@ -27,7 +27,14 @@ fn fetchThread(state: *AppState) !void {
     var curl = Curl.init() orelse return;
     defer curl.deinit();
 
-    while (state.departure_screen_state.fetch_thread != null) {
+    while (true) {
+        {
+            state.departure_screen_state.mutex.lock();
+            defer state.departure_screen_state.mutex.unlock();
+            if (state.departure_screen_state.fetch_thread == null) {
+                break;
+            }
+        }
         var fetch_anyway = state.departure_screen_state.should_refresh;
         if (state.departure_screen_state.last_refresh_time + 30000 < std.time.milliTimestamp()) {
             fetch_anyway = true;
@@ -635,6 +642,9 @@ pub fn render(state: *AppState) !void {
         switch (key) {
             rl.KEY_LEFT => {
                 state.screen = .home;
+                ds.mutex.lock();
+                defer ds.mutex.unlock();
+                ds.fetch_thread = null;
             },
             rl.KEY_R => {
                 ds.should_refresh = true;
@@ -666,7 +676,10 @@ pub fn render(state: *AppState) !void {
 
     {
         ds.mutex.lock();
-        defer ds.mutex.unlock();
+        defer {
+            ds.mutex.unlock();
+            _ = std.Thread.yield() catch null;
+        }
         switch (ds.render_style) {
             .db1 => try draw_db1(state),
             .ns => try draw_ns(state),

src/home.zig

@@ -102,7 +102,10 @@ pub fn render(state: *AppState) !void {
     }
 
     state.home_screen_state.mutex.lock();
-    defer state.home_screen_state.mutex.unlock();
+    defer {
+        state.home_screen_state.mutex.unlock();
+        _ = std.Thread.yield() catch null;
+    }
 
     while (raylib.GetKeyPressed()) |key| {
         switch (key) {