无法使用java.nio.channels.FileLock在Linux上锁定文件

Question

我正在用Java创建一个应用程序，对于该应用程序我只希望运行一个实例。为此，我创建了一个文件，并在我的应用程序运行时锁定了它。

我有以下代码可在Windows上运行，但在Linux上无法运行：一旦我获得了一个锁而没有将其解锁，则可以再获得一个锁。

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;

public class MyApp {

private static File f;
private static FileChannel channel;
private static FileLock lock;

public static void main(String[] args) {
    try {
        f = new File("RingOnRequest.lock");
        // Check if the lock exist
        if (f.exists()) {
            // if exist try to delete it
            f.delete();
        }
        // Try to get the lock
        channel = new RandomAccessFile(f, "rw").getChannel();
        lock = channel.tryLock();
        if(lock == null)
        {
            // File is lock by other application
            channel.close();
            throw new RuntimeException("Only 1 instance of MyApp can run.");
        }
        // Add shutdown hook to release lock when application shutdown
        ShutdownHook shutdownHook = new ShutdownHook();
        Runtime.getRuntime().addShutdownHook(shutdownHook);

        //Your application tasks here..
        System.out.println("Running");
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
    catch(IOException e)
    {
        throw new RuntimeException("Could not start process.", e);
    }

}

public static void unlockFile() {
    // release and delete file lock
    try {
        if(lock != null) {
            lock.release();
            channel.close();
            f.delete();
        }
    } catch(IOException e) {
        e.printStackTrace();
    }
}

static class ShutdownHook extends Thread {

    public void run() {
        unlockFile();
    }
}

}

Answer 1

我使用了与您相同的示例，并且在Mac OS
X上遇到了同样的问题。似乎文件锁定不能防止在POSIX系统上删除文件。在解锁之前，您的应用仍会对该文件具有某种处理方式。因此，请考虑使用名称为PID的锁定文件（或内部文件）。