vincent4vx / SingleInstance

 * This file is part of SingleInstance.

 *

 * SingleInstance is free software: you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * SingleInstance is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with SingleInstance.  If not, see <https://www.gnu.org/licenses/>.

 *

 * Copyright (c) 2020 Vincent Quatrevieux

 */

package fr.quatrevieux.singleinstance;

import fr.quatrevieux.singleinstance.ipc.InstanceServer;

import fr.quatrevieux.singleinstance.ipc.Message;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import java.io.IOException;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.function.Consumer;

/**

 * Facade for a simple usage of {@link InstanceManager}

 *

 * Usage:

 * <pre>{@code

 *     public static void main(String[] args) {

 *         // Check if an instance is running

 *         SingleInstance.onAlreadyRunning(instance -> {

 *             // Send the argument to the instance and stop the current process

 *             instance.send("Open", args[0].getBytes());

 *             System.exit(0);

 *         });

 *

 *         // Initialize application

 *         MyApp app = xxx;

 *

 *         // Start the IPC server

 *         SingleInstance.onMessage(message -> {

 *             // Receive an "Open" message

 *             if (message.name().equals("Open")) {

 *                 app.open(new String(message.data()));

 *             }

 *         });

 *     }

 * }</pre>

 */

final public class SingleInstance {

    static private InstanceManager manager;

    static private InstanceServer server;

    static private ExecutorService executor;

    static private DistantInstance distantInstance;

    static private Thread shutdownHook;

    final static private Logger LOGGER = LoggerFactory.getLogger(SingleInstance.class);

    /**

     * Initialize the SingleInstance system

     * Calling this method is not required : any other call will implicitly call this method

     *

     * @throws IOException When error occurs during acquiring the lock

     */

    static public void init() throws IOException {

        init(null);

    }

    /**

     * Initialize the SingleInstance system by specifying the lock file

     *

     * @param lockFile The lock file to use

     *

     * @throws IOException When error occurs during acquiring the lock

     */

    }

    /**

     * Check if the current process is the first running instance

     *

     * Usage:

     * <pre>{@code

     *     public static void main(String[] args) {

     *         if (!SingleInstance.isFirst()) {

     *             System.err.println("Already running");

     *             return;

     *         }

     *     }

     * }</pre>

     *

     * @return true if the current process is the first running instance

     *

     * @throws IOException When cannot initialize system

     * @see SingleInstance#onAlreadyRunning(Consumer) For perform action when an instance is already running

     */

    static public boolean isFirst() throws IOException {

        return manager().acquire();

    }

    /**

     * Start the IPC server if the current process is the first running instance,

     * and handle received messages

     *

     * If the current process is not the first running instance, this method will be a noop.

     *

     * Note: This method will start a new thread to consume messages

     *

     * <pre>{@code

     *     SingleInstance.onMessage(message -> {

     *         if (message.name().equals("MyMessage")) {

     *             // Handle message

     *         }

     *     });

     * }</pre>

     *

     * @param consumer The action to perform when receiving messages

     *

     * @throws IOException When cannot start the server

     * @throws IllegalStateException When the server is already started

     */

    static public void onMessage(Consumer<Message> consumer) throws IOException {

        if (server != null) {

            throw new IllegalStateException("IPC Server is already started");

        }

        manager().server().ifPresent(server -> {

            SingleInstance.server = server;

            executor = Executors.newSingleThreadExecutor();

            executor.execute(() -> {

                try {

                    server.consume(consumer);

                } catch (IOException e) {

                    LOGGER.error("Error during reading message on IPC server", e);

                }

            });

        });

    }

    /**

     * Perform action is an already running instance is found

     *

     * Usage:

     * <pre>{@code

     *     SingleInstance.onAlreadyRunning(instance -> {

     *         instance.send("MyMessage"); // Send a message to the running instance

     *         System.exit(0); // Stop the current process

     *     });

     * }</pre>

     *

     * @param action Action to perform

     *

     * @throws IOException When cannot initialize the system

     */

    static public void onAlreadyRunning(Consumer<DistantInstance> action) throws IOException {

        if (distantInstance != null) {

            action.accept(distantInstance);

            return;

        }

        manager().find().ifPresent(instance -> {

            distantInstance = instance;

            action.accept(distantInstance);

        });

    }

    /**

     * Get (or create) the instance manager instance

     *

     * @return The manager instance

     * @throws IOException When cannot initialize the system

     */

    static public InstanceManager manager() throws IOException {

        init();

        return manager;

    }

    /**

     * Close the SingleInstance system and release the lock

     * This method should not be called manually : when init is called, a shutdown hook is registered

     */

    static public void close() {

        if (manager == null) {

            return;

        }

        if (server != null) {

            try {

                server.close();

            } catch (IOException e) {

                LOGGER.error("Error during closing the IPC server", e);

            }

            server = null;

        }

        if (executor != null) {

            executor.shutdown();

            executor = null;

        }

        distantInstance = null;

        manager.release();

    }

}