[executorch][android] Add Runtime.java to centralize native library loading

Author: Lefteris Gilmaz

extension/android/executorch_android/src/main/java/org/pytorch/executorch/Runtime.java

@@ -0,0 +1,28 @@
+package org.pytorch.executorch;
+
+import com.facebook.soloader.nativeloader.NativeLoader;
+import com.facebook.soloader.nativeloader.SystemDelegate;
+import com.facebook.jni.annotations.DoNotStrip;
+
+public class Runtime {
+    private static boolean initialized = false;
+
+    static {
+        if (!NativeLoader.isInitialized()) {
+            NativeLoader.init(new SystemDelegate());
+        }
+        // Loads libexecutorch.so from jniLibs
+        NativeLoader.loadLibrary("executorch");
+        initialized = true;
+    }
+
+    public static boolean isInitialized() {
+        return initialized;
+    }
+
+    @DoNotStrip
+    public static native String[] getRegisteredOps();
+
+    @DoNotStrip
+    public static native String[] getRegisteredBackends();
+}

extension/android/executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmModule.java

@@ -13,6 +13,7 @@
 import com.facebook.soloader.nativeloader.NativeLoader;
 import com.facebook.soloader.nativeloader.SystemDelegate;
 import org.pytorch.executorch.annotations.Experimental;
+import org.pytorch.executorch.Runtime;
 
 /**
  * LlmModule is a wrapper around the Executorch LLM. It provides a simple interface to generate text
@@ -27,11 +28,9 @@ public class LlmModule {
   public static final int MODEL_TYPE_TEXT_VISION = 2;
 
   static {
-    if (!NativeLoader.isInitialized()) {
-      NativeLoader.init(new SystemDelegate());
+    if (!Runtime.isInitialized()) {
+        throw new IllegalStateException("ExecuTorch runtime not initialized.");
     }
-    NativeLoader.loadLibrary("executorch");
-  }
 
   private final HybridData mHybridData;
   private static final int DEFAULT_SEQ_LEN = 128;