[java] Adding ability to load a model from a memory mapped byte buffer (#20062)

### Description
Adds support for constructing an `OrtSession` from a
`java.nio.ByteBuffer`. These buffers can be memory mapped from files
which means there doesn't need to be copies of the model protobuf held
in Java, reducing peak memory usage during session construction.

### Motivation and Context
Reduces memory usage on model construction by not requiring as many
copies on the Java side. Should help with #19599.

java/src/main/java/ai/onnxruntime/OrtEnvironment.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024 Oracle and/or its affiliates. All rights reserved.
  * Licensed under the MIT License.
  */
 package ai.onnxruntime;
@@ -7,6 +7,7 @@ package ai.onnxruntime;
 import ai.onnxruntime.OrtSession.SessionOptions;
 import ai.onnxruntime.OrtTrainingSession.OrtCheckpointState;
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.EnumSet;
 import java.util.Objects;
 import java.util.logging.Logger;
@@ -236,6 +237,52 @@ public final class OrtEnvironment implements AutoCloseable {
     return new OrtSession(this, modelPath, allocator, options);
   }
 
+  /**
+   * Create a session using the specified {@link SessionOptions}, model and the default memory
+   * allocator.
+   *
+   * @param modelBuffer Byte buffer representing an ONNX model. Must be a direct byte buffer.
+   * @param options The session options.
+   * @return An {@link OrtSession} with the specified model.
+   * @throws OrtException If the model failed to parse, wasn't compatible or caused an error.
+   */
+  public OrtSession createSession(ByteBuffer modelBuffer, SessionOptions options)
+      throws OrtException {
+    return createSession(modelBuffer, defaultAllocator, options);
+  }
+
+  /**
+   * Create a session using the default {@link SessionOptions}, model and the default memory
+   * allocator.
+   *
+   * @param modelBuffer Byte buffer representing an ONNX model. Must be a direct byte buffer.
+   * @return An {@link OrtSession} with the specified model.
+   * @throws OrtException If the model failed to parse, wasn't compatible or caused an error.
+   */
+  public OrtSession createSession(ByteBuffer modelBuffer) throws OrtException {
+    return createSession(modelBuffer, new OrtSession.SessionOptions());
+  }
+
+  /**
+   * Create a session using the specified {@link SessionOptions} and model buffer.
+   *
+   * @param modelBuffer Byte buffer representing an ONNX model. Must be a direct byte buffer.
+   * @param allocator The memory allocator to use.
+   * @param options The session options.
+   * @return An {@link OrtSession} with the specified model.
+   * @throws OrtException If the model failed to parse, wasn't compatible or caused an error.
+   */
+  OrtSession createSession(ByteBuffer modelBuffer, OrtAllocator allocator, SessionOptions options)
+      throws OrtException {
+    Objects.requireNonNull(modelBuffer, "model array must not be null");
+    if (modelBuffer.remaining() == 0) {
+      throw new OrtException("Invalid model buffer, no elements remaining.");
+    } else if (!modelBuffer.isDirect()) {
+      throw new OrtException("ByteBuffer is not direct.");
+    }
+    return new OrtSession(this, modelBuffer, allocator, options);
+  }
+
   /**
    * Create a session using the specified {@link SessionOptions}, model and the default memory
    * allocator.

java/src/main/java/ai/onnxruntime/OrtSession.java

@@ -11,6 +11,7 @@ import ai.onnxruntime.providers.OrtCUDAProviderOptions;
 import ai.onnxruntime.providers.OrtFlags;
 import ai.onnxruntime.providers.OrtTensorRTProviderOptions;
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -94,6 +95,31 @@ public class OrtSession implements AutoCloseable {
         allocator);
   }
 
+  /**
+   * Creates a session reading the model from the supplied byte buffer.
+   *
+   * <p>Must be a direct byte buffer.
+   *
+   * @param env The environment.
+   * @param modelBuffer The model protobuf as a byte buffer.
+   * @param allocator The allocator to use.
+   * @param options Session configuration options.
+   * @throws OrtException If the model was corrupted or some other error occurred in native code.
+   */
+  OrtSession(
+      OrtEnvironment env, ByteBuffer modelBuffer, OrtAllocator allocator, SessionOptions options)
+      throws OrtException {
+    this(
+        createSession(
+            OnnxRuntime.ortApiHandle,
+            env.getNativeHandle(),
+            modelBuffer,
+            modelBuffer.position(),
+            modelBuffer.remaining(),
+            options.getNativeHandle()),
+        allocator);
+  }
+
   /**
    * Private constructor to build the Java object wrapped around a native session.
    *
@@ -514,6 +540,15 @@ public class OrtSession implements AutoCloseable {
   private static native long createSession(
       long apiHandle, long envHandle, byte[] modelArray, long optsHandle) throws OrtException;
 
+  private static native long createSession(
+      long apiHandle,
+      long envHandle,
+      ByteBuffer modelBuffer,
+      int bufferPos,
+      int bufferSize,
+      long optsHandle)
+      throws OrtException;
+
   private native long getNumInputs(long apiHandle, long nativeHandle) throws OrtException;
 
   private native String[] getInputNames(long apiHandle, long nativeHandle, long allocatorHandle)

java/src/main/native/ai_onnxruntime_OrtSession.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2020, 2022 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024 Oracle and/or its affiliates. All rights reserved.
  * Licensed under the MIT License.
  */
 #include <jni.h>
@@ -48,6 +48,29 @@ JNIEXPORT jlong JNICALL Java_ai_onnxruntime_OrtSession_createSession__JJLjava_la
   return (jlong)session;
 }
 
+/*
+ * Class:     ai_onnxruntime_OrtSession
+ * Method:    createSession
+ * Signature: (JJLjava/nio/ByteBuffer;IIJ)J
+ */
+JNIEXPORT jlong JNICALL Java_ai_onnxruntime_OrtSession_createSession__JJLjava_nio_ByteBuffer_2IIJ(JNIEnv* jniEnv, jclass jclazz, jlong apiHandle, jlong envHandle, jobject buffer, jint bufferPos, jint bufferSize, jlong optsHandle) {
+  (void)jclazz;  // Required JNI parameter not needed by functions which don't need to access their host object.
+  const OrtApi* api = (const OrtApi*)apiHandle;
+  OrtEnv* env = (OrtEnv*)envHandle;
+  OrtSessionOptions* opts = (OrtSessionOptions*)optsHandle;
+  OrtSession* session = NULL;
+
+  // Extract the buffer
+  char* bufferArr = (char*)(*jniEnv)->GetDirectBufferAddress(jniEnv, buffer);
+  // Increment by bufferPos bytes
+  bufferArr = bufferArr + bufferPos;
+
+  // Create the session
+  checkOrtStatus(jniEnv, api, api->CreateSessionFromArray(env, bufferArr, bufferSize, opts, &session));
+
+  return (jlong)session;
+}
+
 /*
  * Class:     ai_onnxruntime_OrtSession
  * Method:    createSession

java/src/test/java/ai/onnxruntime/InferenceTest.java

@@ -20,10 +20,14 @@ import ai.onnxruntime.OrtSession.SessionOptions.ExecutionMode;
 import ai.onnxruntime.OrtSession.SessionOptions.OptLevel;
 import java.io.File;
 import java.io.IOException;
+import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.FloatBuffer;
 import java.nio.LongBuffer;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileChannel.MapMode;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -338,6 +342,33 @@ public class InferenceTest {
     }
   }
 
+  @Test
+  public void createSessionFromByteBuffer() throws IOException, OrtException {
+    Path modelPath = TestHelpers.getResourcePath("/squeezenet.onnx");
+    try (RandomAccessFile file = new RandomAccessFile(modelPath.toFile(), "r");
+        FileChannel channel = file.getChannel()) {
+      MappedByteBuffer modelBuffer = channel.map(MapMode.READ_ONLY, 0, channel.size());
+      try (OrtSession.SessionOptions options = new SessionOptions();
+          OrtSession session = env.createSession(modelBuffer, options)) {
+        assertNotNull(session);
+        assertEquals(1, session.getNumInputs()); // 1 input node
+        Map<String, NodeInfo> inputInfoList = session.getInputInfo();
+        assertNotNull(inputInfoList);
+        assertEquals(1, inputInfoList.size());
+        NodeInfo input = inputInfoList.get("data_0");
+        assertEquals("data_0", input.getName()); // input node name
+        assertTrue(input.getInfo() instanceof TensorInfo);
+        TensorInfo inputInfo = (TensorInfo) input.getInfo();
+        assertEquals(OnnxJavaType.FLOAT, inputInfo.type);
+        int[] expectedInputDimensions = new int[] {1, 3, 224, 224};
+        assertEquals(expectedInputDimensions.length, inputInfo.shape.length);
+        for (int i = 0; i < expectedInputDimensions.length; i++) {
+          assertEquals(expectedInputDimensions[i], inputInfo.shape[i]);
+        }
+      }
+    }
+  }
+
   @Test
   public void createSessionFromByteArray() throws IOException, OrtException {
     Path modelPath = TestHelpers.getResourcePath("/squeezenet.onnx");