fix: prevent file I/O on audio thread, add safety guard in display mode lambda

- oboe_bridge.cpp: eagerly compute big-core mask in start() so the
  audio callback never calls computeBigCoreMask() (which does fopen).
  Defensive fallback in callback uses upper-half heuristic instead of
  file I/O if cache is somehow cold.
- OsuGameAndroid.cs: wrap Schedule lambda in SelectHighestRefreshRate()
  with try-catch to prevent unhandled exceptions from stale display
  references.

Agent-Logs-Url: https://github.com/winnerspiros/osu/sessions/df8487e1-1028-44d9-adc9-42e5e885e5a3

Co-authored-by: winnerspiros <1675249+winnerspiros@users.noreply.github.com>

Author: Copilot

osu.Android/Native/oboe_bridge.cpp

@@ -171,6 +171,17 @@ bool OboeBridge::start() {
 
     active_.store(true);
     affinitySet_.store(false);
+
+    // Eagerly compute and cache the big-core mask BEFORE the audio callback runs.
+    // This ensures computeBigCoreMask() (which does file I/O via fopen on sysfs)
+    // never executes on the real-time audio thread where it could cause latency
+    // spikes or priority inversion.
+    int mask = cachedBigCoreMask.load(std::memory_order_relaxed);
+    if (mask < 0) {
+        mask = computeBigCoreMask();
+        cachedBigCoreMask.store(mask, std::memory_order_relaxed);
+    }
+
     LOGI("Oboe stream started");
     return true;
 }
@@ -272,9 +283,20 @@ oboe::DataCallbackResult OboeBridge::onAudioReady(
         // Uses sysfs-based topology detection for accurate big-core identification
         // across all SoC vendors (Snapdragon, Exynos, Dimensity, Tensor).
         if (!affinitySet_.load(std::memory_order_relaxed)) {
+            // cachedBigCoreMask is eagerly computed in start(), so this load
+            // should always return >= 0.  The < 0 branch is a defensive fallback
+            // that avoids file I/O — it uses the generic upper-half heuristic
+            // instead of calling computeBigCoreMask() on the audio thread.
             int bigMask = cachedBigCoreMask.load(std::memory_order_relaxed);
             if (bigMask < 0) {
-                bigMask = computeBigCoreMask();
+                // Defensive: sysfs was never read (should not happen).
+                // Use upper-half heuristic instead of doing file I/O here.
+                int num_cores = sysconf(_SC_NPROCESSORS_CONF);
+                bigMask = 0;
+                if (num_cores > 1) {
+                    for (int i = num_cores / 2; i < std::min(num_cores, 32); ++i)
+                        bigMask |= (1 << i);
+                }
                 cachedBigCoreMask.store(bigMask, std::memory_order_relaxed);
             }
 

osu.Android/OsuGameAndroid.cs

@@ -483,15 +483,22 @@ public void SelectHighestRefreshRate()
 
                 Schedule(() =>
                 {
-                    AvailableDisplayRefreshRates.Clear();
-                    AvailableDisplayRefreshRates.Add(0); // 0 = "Auto (highest)"
-                    AvailableDisplayRefreshRates.AddRange(rates);
-
-                    // If user hasn't selected a rate, auto-select highest.
-                    if (SelectedDisplayRefreshRate.Value == 0)
-                        applyDisplayMode(display, modes.OrderByDescending(m => m.RefreshRate).First());
-                    else
-                        applyRefreshRate(SelectedDisplayRefreshRate.Value);
+                    try
+                    {
+                        AvailableDisplayRefreshRates.Clear();
+                        AvailableDisplayRefreshRates.Add(0); // 0 = "Auto (highest)"
+                        AvailableDisplayRefreshRates.AddRange(rates);
+
+                        // If user hasn't selected a rate, auto-select highest.
+                        if (SelectedDisplayRefreshRate.Value == 0)
+                            applyDisplayMode(display, modes.OrderByDescending(m => m.RefreshRate).First());
+                        else
+                            applyRefreshRate(SelectedDisplayRefreshRate.Value);
+                    }
+                    catch (Exception ex)
+                    {
+                        Debug.WriteLine($"[osu!] Failed to apply initial display mode: {ex.Message}");
+                    }
                 });
 
                 Logger.Log($"[osu!] Display modes queried: {string.Join(", ", rates.Select(r => $"{r}Hz"))} (DeX={gameActivity.IsDeX})", LoggingTarget.Performance);