lib: optimize engine loader; always perform a fresh detection when cache is null

examples/llama.android/llama/src/main/java/android/llama/cpp/TierDetection.kt

@@ -13,7 +13,7 @@ interface TierDetection {
  * Higher tiers provide better performance on supported hardware.
  */
 enum class LLamaTier(val rawValue: Int, val libraryName: String, val description: String) {
-    NONE(404, "", "No valid Arm optimization available!"),
+    NONE(-404, "", "No valid Arm optimization available!"),
     T0(0, "llama_android_t0", "ARMv8-a baseline with SIMD"),
     T1(1, "llama_android_t1", "ARMv8.2-a with DotProd"),
     T2(2, "llama_android_t2", "ARMv8.6-a with DotProd + I8MM"),

examples/llama.android/llama/src/main/java/android/llama/cpp/internal/InferenceEngineLoader.kt

@@ -42,9 +42,7 @@ internal object InferenceEngineLoader {
      * Get the detected tier, loading from cache if needed
      */
     fun getDetectedTier(context: Context): LLamaTier? =
-        _detectedTier ?: runBlocking {
-            loadDetectedTierFromDataStore(context)
-        }
+        _detectedTier ?: runBlocking { obtainTier(context) }
 
     /**
      * Factory method to get a configured [InferenceEngineImpl] instance.
@@ -57,11 +55,7 @@ internal object InferenceEngineLoader {
 
         return runBlocking {
             // Obtain the optimal tier from cache if available
-            val tier = loadDetectedTierFromDataStore(context) ?: run {
-                Log.i(TAG, "Performing fresh tier detection")
-                detectAndSaveOptimalTier(context)
-            }
-
+            val tier = obtainTier(context)
             if (tier == null || tier == LLamaTier.NONE) {
                 Log.e(TAG, "Aborted instantiating Inference Engine due to invalid tier")
                 return@runBlocking null
@@ -83,14 +77,17 @@ internal object InferenceEngineLoader {
     }
 
     /**
-     * Clear cached detection results (for testing/debugging)
+     * First attempt to load detected tier from storage, if available;
+     * Otherwise, perform a fresh detection, then save to storage and cache.
      */
-    fun clearCache(context: Context) {
-        runBlocking { context.llamaTierDataStore.edit { it.clear() } }
-        _cachedInstance = null
-        _detectedTier = null
-        Log.i(TAG, "Cleared detection results and cached instance")
-    }
+    private suspend fun obtainTier(context: Context) =
+        loadDetectedTierFromDataStore(context) ?: run {
+            Log.i(TAG, "Performing fresh tier detection")
+            performOptimalTierDetection().also { tier ->
+                tier?.saveToDataStore(context)
+                _detectedTier = tier
+            }
+        }
 
     /**
      * Load cached tier from datastore without performing detection
@@ -112,18 +109,9 @@ internal object InferenceEngineLoader {
     }
 
     /**
-     * Detect optimal tier and save to cache
+     * Actual implementation of optimal tier detection via native methods
      */
-    private suspend fun detectAndSaveOptimalTier(context: Context): LLamaTier? =
-        detectOptimalTier().also { tier ->
-            tier?.saveToDataStore(context)
-            _detectedTier = tier
-        }
-
-    /**
-     * Detect optimal tier and save to cache
-     */
-    private fun detectOptimalTier(): LLamaTier? {
+    private fun performOptimalTierDetection(): LLamaTier? {
         try {
             // Load CPU detection library
             System.loadLibrary("llama_cpu_detector")
@@ -141,9 +129,10 @@ internal object InferenceEngineLoader {
             }
 
             // Ensure we don't exceed maximum supported tier
-            return if (tier.rawValue > LLamaTier.maxSupportedTier.rawValue) {
-                Log.w(TAG, "Detected tier ${tier.name} exceeds max supported, using ${LLamaTier.maxSupportedTier.name}")
-                LLamaTier.maxSupportedTier
+            val maxTier = LLamaTier.maxSupportedTier
+            return if (tier.rawValue > maxTier.rawValue) {
+                Log.w(TAG, "Detected tier ${tier.name} exceeds max supported, using ${maxTier.name}")
+                maxTier
             } else {
                 tier
             }
@@ -158,6 +147,16 @@ internal object InferenceEngineLoader {
         }
     }
 
+    /**
+     * Clear cached detection results (for testing/debugging)
+     */
+    fun clearCache(context: Context) {
+        runBlocking { context.llamaTierDataStore.edit { it.clear() } }
+        _cachedInstance = null
+        _detectedTier = null
+        Log.i(TAG, "Cleared detection results and cached instance")
+    }
+
     private suspend fun LLamaTier.saveToDataStore(context: Context) {
         context.llamaTierDataStore.edit { prefs ->
             prefs[DETECTED_TIER] = this.rawValue