Add LLM inference support to JMLC API

src/main/java/org/apache/sysds/api/jmlc/Connection.java

@@ -28,7 +28,11 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Map;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.sysds.hops.OptimizerUtils;
@@ -66,6 +70,7 @@
 import org.apache.sysds.runtime.transform.meta.TfMetaUtils;
 import org.apache.sysds.runtime.util.CollectionUtils;
 import org.apache.sysds.runtime.util.DataConverter;
+import py4j.GatewayServer;
 
 /**
  * Interaction with SystemDS using the JMLC (Java Machine Learning Connector) API is initiated with
@@ -91,6 +96,12 @@ public class Connection implements Closeable
 	private final DMLConfig _dmlconf;
 	private final CompilerConfig _cconf;
 	private static FileSystem fs = null;
+	private Process _pythonProcess = null;
+	private py4j.GatewayServer _gatewayServer = null;
+	private LLMCallback _llmWorker = null;
+	private CountDownLatch _workerLatch = null;
+
+	private static final Log LOG = LogFactory.getLog(Connection.class.getName());
 
 	/**
 	 * Connection constructor, the starting point for any other JMLC API calls.
@@ -287,13 +298,161 @@ public PreparedScript prepareScript(String script, Map<String,String> nsscripts,
 		//return newly create precompiled script 
 		return new PreparedScript(rtprog, inputs, outputs, _dmlconf, _cconf);
 	}
+
+	/**
+	 * Loads a HuggingFace model via Python worker for LLM inference.
+	 * Uses auto-detected available ports for Py4J communication.
+	 * 
+	 * @param modelName HuggingFace model name 
+	 * @param workerScriptPath path to the Python worker script 
+	 * @return LLMCallback interface to the Python worker
+	 */
+	public LLMCallback loadModel(String modelName, String workerScriptPath) {
+		//auto-find available ports
+		int javaPort = findAvailablePort();
+		int pythonPort = findAvailablePort();
+		return loadModel(modelName, workerScriptPath, javaPort, pythonPort);
+	}
+
+	/**
+	 * Loads a HuggingFace model via Python worker for LLM inference.
+	 * Starts a Python subprocess and connects via Py4J.
+	 * 
+	 * @param modelName HuggingFace model name
+	 * @param workerScriptPath path to the Python worker script 
+	 * @param javaPort port for Java gateway server
+	 * @param pythonPort port for Python callback server
+	 * @return LLMCallback interface to the Python worker
+	 */
+	public LLMCallback loadModel(String modelName, String workerScriptPath, int javaPort, int pythonPort) {
+		if (_llmWorker != null)
+			return _llmWorker;
+		try {
+			//initialize latch for worker registration
+			_workerLatch = new CountDownLatch(1);
+
+			//start Py4J gateway server with callback support
+			_gatewayServer = new GatewayServer.GatewayServerBuilder()
+				.entryPoint(this)
+				.javaPort(javaPort)
+				.callbackClient(pythonPort, java.net.InetAddress.getLoopbackAddress())
+				.build();
+			_gatewayServer.start();
+
+			//give gateway time to start
+			Thread.sleep(500);
+
+			//start python worker process with both ports
+			String pythonCmd = findPythonCommand();
+			LOG.info("Starting LLM worker with script: " + workerScriptPath + 
+				" (python=" + pythonCmd + ", javaPort=" + javaPort + ", pythonPort=" + pythonPort + ")");
+			_pythonProcess = new ProcessBuilder(
+				pythonCmd, workerScriptPath, modelName, 
+				String.valueOf(javaPort), String.valueOf(pythonPort)
+			).redirectErrorStream(true).start();
+
+			//read python output in background thread
+			Thread outputReader = new Thread(() -> {
+				try (BufferedReader reader = new BufferedReader(
+						new InputStreamReader(_pythonProcess.getInputStream()))) {
+					String line;
+					while ((line = reader.readLine()) != null) {
+						LOG.info("[LLM Worker] " + line);
+					}
+				} catch (IOException e) {
+					LOG.error("Error reading LLM worker output", e);
+				}
+			});
+			outputReader.setName("llm-worker-output");
+			outputReader.setDaemon(true);
+			outputReader.start();
+
+			//wait for worker to register, checking process liveness periodically
+			long deadlineNs = System.nanoTime() + TimeUnit.SECONDS.toNanos(60);
+			while (!_workerLatch.await(2, TimeUnit.SECONDS)) {
+				if (!_pythonProcess.isAlive()) {
+					int exitCode = _pythonProcess.exitValue();
+					throw new DMLException("LLM worker process died during startup (exit code " + exitCode + ")");
+				}
+				if (System.nanoTime() > deadlineNs) {
+					throw new DMLException("Timeout waiting for LLM worker to register (60s)");
+				}
+			}
+
+		} catch (DMLException e) {
+			throw e;
+		} catch (Exception e) {
+			throw new DMLException("Failed to start LLM worker: " + e.getMessage());
+		}
+		return _llmWorker;
+	}
+
+	/**
+	 * Finds the available Python command, trying python3 first then python.
+	 * @return python command name
+	 */
+	private static String findPythonCommand() {
+		for (String cmd : new String[]{"python3", "python"}) {
+			try {
+				Process p = new ProcessBuilder(cmd, "--version")
+					.redirectErrorStream(true).start();
+				int exitCode = p.waitFor();
+				if (exitCode == 0)
+					return cmd;
+			} catch (Exception e) {
+				//command not found, try next
+			}
+		}
+		throw new DMLException("No Python installation found (tried python3, python)");
+	}
+
+	/**
+	 * Finds an available port on the local machine.
+	 * @return available port number
+	 */
+	private int findAvailablePort() {
+		try (java.net.ServerSocket socket = new java.net.ServerSocket(0)) {
+			socket.setReuseAddress(true);
+			return socket.getLocalPort();
+		} catch (IOException e) {
+			throw new DMLException("Failed to find available port: " + e.getMessage());
+		}
+	}
+
+	/**
+	 * Called by Python worker to register itself via Py4J.
+	 */
+	public void registerWorker(LLMCallback worker) {
+		_llmWorker = worker;
+		if (_workerLatch != null) {
+			_workerLatch.countDown();
+		}
+		LOG.info("LLM worker registered successfully");
+	}
 
 	/**
 	 * Close connection to SystemDS, which clears the
 	 * thread-local DML and compiler configurations.
 	 */
 	@Override
 	public void close() {
+
+		//shutdown LLM worker if running
+		if (_pythonProcess != null) {
+			_pythonProcess.destroyForcibly();
+			try {
+				_pythonProcess.waitFor(5, TimeUnit.SECONDS);
+			} catch (InterruptedException e) {
+				Thread.currentThread().interrupt();
+			}
+			_pythonProcess = null;
+		}
+		if (_gatewayServer != null) {
+			_gatewayServer.shutdown();
+			_gatewayServer = null;
+		}
+		_llmWorker = null;
+
 		//clear thread-local configurations
 		ConfigurationManager.clearLocalConfigs();
 		if( ConfigurationManager.isCodegenEnabled() )

src/main/java/org/apache/sysds/api/jmlc/LLMCallback.java

@@ -0,0 +1,31 @@
+package org.apache.sysds.api.jmlc;
+
+/**
+ * Interface for the Python LLM worker.
+ * The Python side implements this via Py4J callback.
+ */
+public interface LLMCallback {
+
+	/**
+	 * Generates text using the LLM model.
+	 * 
+	 * @param prompt the input prompt text
+	 * @param maxNewTokens maximum number of new tokens to generate
+	 * @param temperature sampling temperature (0.0 = deterministic, higher = more random)
+	 * @param topP nucleus sampling probability threshold
+	 * @return generated text continuation
+	 */
+	String generate(String prompt, int maxNewTokens, double temperature, double topP);
+
+	/**
+	 * Generates text and returns result with token counts as a JSON string.
+	 * Format: {"text": "...", "input_tokens": N, "output_tokens": M}
+	 * 
+	 * @param prompt the input prompt text
+	 * @param maxNewTokens maximum number of new tokens to generate
+	 * @param temperature sampling temperature (0.0 = deterministic, higher = more random)
+	 * @param topP nucleus sampling probability threshold
+	 * @return JSON string with generated text and token counts
+	 */
+	String generateWithTokenCount(String prompt, int maxNewTokens, double temperature, double topP);
+}

src/main/java/org/apache/sysds/api/jmlc/PreparedScript.java

@@ -80,6 +80,9 @@ public class PreparedScript implements ConfigurableAPI
 	private final CompilerConfig _cconf;
 	private HashMap<String, String> _outVarLineage;
 
+	//LLM inference support
+	private LLMCallback _llmWorker = null;
+
 	private PreparedScript(PreparedScript that) {
 		//shallow copy, except for a separate symbol table
 		//and related meta data of reused inputs
@@ -160,6 +163,112 @@ public CompilerConfig getCompilerConfig() {
 		return _cconf;
 	}
 
+	/**
+	 * Sets the LLM worker callback for text generation.
+	 * 
+	 * @param worker the LLM callback interface
+	 */
+	public void setLLMWorker(LLMCallback worker) {
+		_llmWorker = worker;
+	}
+
+	/**
+	 * Gets the LLM worker callback.
+	 * 
+	 * @return the LLM callback interface, or null if not set
+	 */
+	public LLMCallback getLLMWorker() {
+		return _llmWorker;
+	}
+
+	/**
+	 * Generates text using the LLM worker.
+	 * 
+	 * @param prompt the input prompt text
+	 * @param maxNewTokens maximum number of new tokens to generate
+	 * @param temperature sampling temperature (0.0 = deterministic, higher = more random)
+	 * @param topP nucleus sampling probability threshold
+	 * @return generated text
+	 * @throws DMLException if no LLM worker is set
+	 */
+	public String generate(String prompt, int maxNewTokens, double temperature, double topP) {
+		if (_llmWorker == null) {
+			throw new DMLException("No LLM worker set. Call setLLMWorker() first.");
+		}
+		return _llmWorker.generate(prompt, maxNewTokens, temperature, topP);
+	}
+
+	/**
+	 * Generates text for multiple prompts and returns results as a FrameBlock.
+	 * The FrameBlock has two columns: [prompt, generated_text].
+	 * 
+	 * @param prompts array of input prompt texts
+	 * @param maxNewTokens maximum number of new tokens to generate
+	 * @param temperature sampling temperature
+	 * @param topP nucleus sampling probability threshold
+	 * @return FrameBlock with columns [prompt, generated_text]
+	 */
+	public FrameBlock generateBatch(String[] prompts, int maxNewTokens, double temperature, double topP) {
+		if (_llmWorker == null) {
+			throw new DMLException("No LLM worker set. Call setLLMWorker() first.");
+		}
+		//generate text for each prompt
+		String[][] data = new String[prompts.length][2];
+		for (int i = 0; i < prompts.length; i++) {
+			data[i][0] = prompts[i];
+			data[i][1] = _llmWorker.generate(prompts[i], maxNewTokens, temperature, topP);
+		}
+		//create FrameBlock with string schema
+		ValueType[] schema = new ValueType[]{ValueType.STRING, ValueType.STRING};
+		String[] colNames = new String[]{"prompt", "generated_text"};
+		FrameBlock fb = new FrameBlock(schema, colNames);
+		for (String[] row : data)
+			fb.appendRow(row);
+		return fb;
+	}
+
+	/**
+	 * Generates text for multiple prompts and returns results with timing metrics.
+	 * The FrameBlock has five columns: [prompt, generated_text, time_ms, input_tokens, output_tokens].
+	 * 
+	 * @param prompts array of input prompt texts
+	 * @param maxNewTokens maximum number of new tokens to generate
+	 * @param temperature sampling temperature
+	 * @param topP nucleus sampling probability threshold
+	 * @return FrameBlock with columns [prompt, generated_text, time_ms, input_tokens, output_tokens]
+	 */
+	public FrameBlock generateBatchWithMetrics(String[] prompts, int maxNewTokens, double temperature, double topP) {
+		if (_llmWorker == null) {
+			throw new DMLException("No LLM worker set. Call setLLMWorker() first.");
+		}
+		//generate text for each prompt with timing and token counts
+		String[][] data = new String[prompts.length][5];
+		for (int i = 0; i < prompts.length; i++) {
+			long start = System.nanoTime();
+			String json = _llmWorker.generateWithTokenCount(prompts[i], maxNewTokens, temperature, topP);
+			long elapsed = (System.nanoTime() - start) / 1_000_000;
+			//parse JSON response: {"text": "...", "input_tokens": N, "output_tokens": M}
+			try {
+				org.apache.wink.json4j.JSONObject obj = new org.apache.wink.json4j.JSONObject(json);
+				data[i][0] = prompts[i];
+				data[i][1] = obj.getString("text");
+				data[i][2] = String.valueOf(elapsed);
+				data[i][3] = String.valueOf(obj.getInt("input_tokens"));
+				data[i][4] = String.valueOf(obj.getInt("output_tokens"));
+			} catch (Exception e) {
+				throw new DMLException("Failed to parse LLM worker response: " + e.getMessage());
+			}
+		}
+		//create FrameBlock with schema
+		ValueType[] schema = new ValueType[]{
+			ValueType.STRING, ValueType.STRING, ValueType.INT64, ValueType.INT64, ValueType.INT64};
+		String[] colNames = new String[]{"prompt", "generated_text", "time_ms", "input_tokens", "output_tokens"};
+		FrameBlock fb = new FrameBlock(schema, colNames);
+		for (String[] row : data)
+			fb.appendRow(row);
+		return fb;
+	}
+
 	/**
 	 * Binds a scalar boolean to a registered input variable.
 	 *