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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.client.python;

import py4j.GatewayServer;
import py4j.Py4JPythonClient;

import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.util.Map;
import java.util.concurrent.ExecutionException;

import static org.apache.flink.client.python.PythonEnvUtils.CHECK_INTERVAL;
import static org.apache.flink.client.python.PythonEnvUtils.TIMEOUT_MILLIS;

/** The Py4j Gateway Server provides RPC service for user's python process. */
public class PythonGatewayServer {

    /**
     * Main method to start a local GatewayServer on a ephemeral port. It tells python side via a
     * file.
     *
     * See: py4j.GatewayServer.main()
     */
    public static void main(String[] args)
            throws IOException, ExecutionException, InterruptedException {
        GatewayServer gatewayServer = PythonEnvUtils.startGatewayServer();
        PythonEnvUtils.setGatewayServer(gatewayServer);

        int boundPort = gatewayServer.getListeningPort();
        Py4JPythonClient callbackClient = gatewayServer.getCallbackClient();
        int callbackPort = callbackClient.getPort();
        if (boundPort == -1) {
            System.out.println("GatewayServer failed to bind; exiting");
            System.exit(1);
        }

        // Tells python side the port of our java rpc server
        String handshakeFilePath = System.getenv("_PYFLINK_CONN_INFO_PATH");
        File handshakeFile = new File(handshakeFilePath);
        File tmpPath =
                Files.createTempFile(handshakeFile.getParentFile().toPath(), "connection", ".info")
                        .toFile();
        FileOutputStream fileOutputStream = new FileOutputStream(tmpPath);
        DataOutputStream stream = new DataOutputStream(fileOutputStream);
        stream.writeInt(boundPort);
        stream.writeInt(callbackPort);
        stream.close();
        fileOutputStream.close();

        if (!tmpPath.renameTo(handshakeFile)) {
            System.out.println(
                    "Unable to write connection information to handshake file: "
                            + handshakeFilePath
                            + ", now exit...");
            System.exit(1);
        }

        try {
            // This ensures that the server dies if its parent program dies.
            Map entryPoint =
                    (Map) gatewayServer.getGateway().getEntryPoint();

            for (int i = 0; i < TIMEOUT_MILLIS / CHECK_INTERVAL; i++) {
                if (entryPoint.containsKey("Watchdog")) {
                    break;
                }
                Thread.sleep(CHECK_INTERVAL);
            }
            if (!entryPoint.containsKey("Watchdog")) {
                System.out.println("Unable to get the Python watchdog object, now exit.");
                System.exit(1);
            }
            Watchdog watchdog = (Watchdog) entryPoint.get("Watchdog");
            while (watchdog.ping()) {
                Thread.sleep(CHECK_INTERVAL);
            }
            gatewayServer.shutdown();
            System.exit(0);
        } finally {
            System.exit(1);
        }
    }

    /** A simple watch dog interface. */
    public interface Watchdog {
        boolean ping() throws InterruptedException;
    }

    /**
     * This watchdog object is provided to Python side to check whether its parent process is alive.
     */
    public static Watchdog watchdog =
            () -> {
                Thread.sleep(10000);
                return true;
            };
}