lib: replace the factory pattern for deprecated tiered lib loading with single instance pattern

examples/llama.android/app/src/main/java/com/example/llama/di/AppModule.kt

@@ -76,8 +76,7 @@ internal abstract class AppModule {
             return if (USE_STUB_ENGINE) {
                 StubInferenceEngine()
             } else {
-                KleidiLlama.createInferenceEngine(context)
+                KleidiLlama.getInferenceEngine(context)
-                    ?: throw InstantiationException("Cannot instantiate InferenceEngine!")
             }
         }
 

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

@@ -1,7 +1,7 @@
 package android.llama.cpp
 
 import android.content.Context
-import android.llama.cpp.internal.InferenceEngineFactory
+import android.llama.cpp.internal.InferenceEngineImpl
 import android.llama.cpp.internal.TierDetectionImpl
 
 /**
@@ -10,12 +10,12 @@ import android.llama.cpp.internal.TierDetectionImpl
  */
 object KleidiLlama {
     /**
-     * Create an inference engine instance with automatic tier detection.
+     * Get the inference engine single instance.
      */
-    fun createInferenceEngine(context: Context) = InferenceEngineFactory.getInstance(context)
+    fun getInferenceEngine(context: Context) = InferenceEngineImpl.getInstance(context)
 
     /**
-     * Get tier detection information for debugging/settings.
+     * Get tier detection single instance.
      */
-    fun getTierDetection(context: Context): TierDetection = TierDetectionImpl(context)
+    fun getTierDetection(context: Context): TierDetection = TierDetectionImpl.getInstance(context)
 }

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

@@ -1,45 +0,0 @@
-package android.llama.cpp.internal
-
-import android.content.Context
-import android.llama.cpp.InferenceEngine
-import android.llama.cpp.TierDetection
-import android.util.Log
-import kotlinx.coroutines.runBlocking
-
-/**
- * Internal factory to create [InferenceEngine] and [TierDetection]
- */
-internal object InferenceEngineFactory {
-    private val TAG = InferenceEngineFactory::class.simpleName
-
-    private var _cachedInstance: InferenceEngineImpl? = null
-
-    /**
-     * Factory method to get a configured [InferenceEngineImpl] instance.
-     * Handles tier detection, caching, and library loading automatically.
-     */
-    @Synchronized
-    fun getInstance(context: Context): InferenceEngine? {
-        // Return cached instance if available
-        _cachedInstance?.let { return it }
-
-        return runBlocking {
-            try {
-                // Create and cache the inference engine instance
-                InferenceEngineImpl.create(context).also {
-                    _cachedInstance = it
-                    Log.i(TAG, "Successfully instantiated Inference Engine")
-                }
-
-            } catch (e: Exception) {
-                Log.e(TAG, "Error instantiating Inference Engine", e)
-                null
-            }
-        }
-    }
-
-    fun clearCache() {
-        _cachedInstance = null
-        Log.i(TAG, "Cleared cached instance of InferenceEngine")
-    }
-}

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

@@ -29,7 +29,7 @@ import java.io.IOException
  * with the underlying C++ native code.
  *
  * The typical usage flow is:
- * 1. Get instance via [instance]
+ * 1. Get instance via [getInstance]
  * 2. Load a model with [loadModel]
  * 3. Send prompts with [sendUserPrompt]
  * 4. Generate responses as token streams
@@ -47,30 +47,29 @@ internal class InferenceEngineImpl private constructor(
     companion object {
         private val TAG = InferenceEngineImpl::class.java.simpleName
 
-        private var initialized = false
+        @Volatile
+        private var instance: InferenceEngine? = null
 
         /**
-         * Create [InferenceEngineImpl] instance at runtime
+         * Create or obtain [InferenceEngineImpl]'s single instance.
          *
          * @param Context for obtaining native library directory
          * @throws IllegalArgumentException if native library path is invalid
          * @throws UnsatisfiedLinkError if library failed to load
          */
-        internal fun create(context: Context): InferenceEngineImpl {
+        internal fun getInstance(context: Context) =
-            assert(!initialized) { "Inference Engine has already been initialized!" }
+            instance ?: synchronized(this) {
+                val nativeLibDir = context.applicationInfo.nativeLibraryDir
+                require(nativeLibDir.isNotBlank()) { "Expected a valid native library path!" }
 
-            val nativeLibDir = context.applicationInfo.nativeLibraryDir
+                try {
-            require(nativeLibDir.isNotBlank()) { "Expected native library" }
+                    Log.i(TAG, "Instantiating InferenceEngineImpl,,,")
-
+                    InferenceEngineImpl(nativeLibDir).also { instance = it }
-            return try {
+                } catch (e: UnsatisfiedLinkError) {
-                Log.i(TAG, "Instantiating InferenceEngineImpl,,,")
+                    Log.e(TAG, "Failed to load native library from $nativeLibDir", e)
-                InferenceEngineImpl(nativeLibDir).also { initialized = true }
+                    throw e
-
+                }
-            } catch (e: UnsatisfiedLinkError) {
-                Log.e(TAG, "Failed to load native library from $nativeLibDir", e)
-                throw e
             }
-        }
     }
 
     /**

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

@@ -15,7 +15,7 @@ import kotlinx.coroutines.runBlocking
 /**
  * Internal [LLamaTier] detection implementation
  */
-internal class TierDetectionImpl(
+internal class TierDetectionImpl private constructor(
     private val context: Context
 ): TierDetection {
 
@@ -30,6 +30,19 @@ internal class TierDetectionImpl(
 
         private val DETECTION_VERSION = intPreferencesKey("detection_version")
         private val DETECTED_TIER = intPreferencesKey("detected_tier")
+
+        @Volatile
+        private var instance: TierDetection? = null
+
+        /**
+         * Create or obtain [TierDetectionImpl]'s single instance.
+         *
+         * @param Context for obtaining the data store
+         */
+        internal fun getInstance(context: Context) =
+            instance ?: synchronized(this) {
+                instance ?: TierDetectionImpl(context).also { instance = it }
+            }
     }
 
     private external fun getOptimalTier(): Int