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 java.io.IOException;

import java.lang.management.ManagementFactory;

import java.util.Optional;

/**

 * Handle single instance system

 *

 * Usage :

 * <pre>{@code

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

 *         // Check single instance

 *         InstanceManager manager = new InstanceManager();

 *

 *         manager.find().ifPresent(distant -> {

 *             // A running instance is present : send a message and close the application

 *             distant.send("My message", args[0].getBytes());

 *             System.exit(0);

 *         });

 *

 *         // Initialize application

 *         MyApp app = xxx;

 *

 *         // Start the IPC server

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

 *             server.consume(message -> app.handleMessage(message));

 *         });

 *     }

 * }</pre>

 */

final public class InstanceManager {

    final private LockFile lockFile;

    public InstanceManager() {

        this(new LockFile());

    }

    public InstanceManager(LockFile lockFile) {

        this.lockFile = lockFile;

    }

    /**

     * Try to acquire the single instance (i.e. the lock file)

     * If the lock is acquired, the PID will be written on

     *

     * @return true if the current process as acquire the lock

     *

     * @throws IOException When cannot access to lock file

     */

    public boolean acquire() throws IOException {

        if (lockFile.acquire()) {

            lockFile.write(output -> output.writeInt(getCurrentPid()));

            return true;

        }

        return false;

    }

    /**

     * Try to get the distant instance (the first run process)

     *

     * Usage:

     * <pre>{@code

     *     InstanceManager im = new InstanceManager();

     *     im.find().ifPresent(distant -> {

     *         System.out.println("Process already running");

     *         // Send a message to the first process

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

     *         System.exit(0);

     *     });

     * }</pre>

     *

     * @return An empty optional if the current process is the first running, or the distant instance if exists

     *

     * @throws IOException When cannot access to lock file

     */

    public Optional<DistantInstance> find() throws IOException {

        return acquire() ? Optional.empty() : Optional.of(new DistantInstance(lockFile));

    }

    /**

     * Try to open the IPC server

     * If the server is successfully opened, the port number will be written on the lock file

     *

     * Usage:

     * <pre>{@code

     *     InstanceManager im = new InstanceManager();

     *     im.server().ifPresent(server -> {

     *         server.consume(message -> {

     *             // Process received messages

     *             if (message.name().equals(xxx)) {

     *                 // ...

     *             }

     *         });

     *     });

     * }</pre>

     *

     * @return An empty optional if the current process is not the first running instance

     *

     * @throws IOException When cannot open the server

     */

    /**

     * Release the lock file

     */

    public void release() {

        lockFile.release();

    }

    private int getCurrentPid() {

        return Integer.parseInt(ManagementFactory.getRuntimeMXBean().getName().split("@", 2)[0]);

    }

}