java - 为什么锁定文件时会发生 OverlappingFileLockException？

Question

我尝试锁定一个文件并用下面的代码写入它:

public class TrainSetBuildTask implements Runnable {
    private String pathname;
    public TrainSetBuildTask(String pathname){
        this.pathname = pathname;
    }

    @Override
    public void run() {
          try {
              String content = "content\n";
             //write to a file
             FileOutputStream os = new FileOutputStream(new File(pathname), true);
             FileChannel channel = os.getChannel();
             FileLock lock = channel.tryLock();
             if (lock != null) {
                ByteBuffer bytes = ByteBuffer.wrap(content.getBytes()); 
                channel.write(bytes);
                lock.release();
             }
             channel.close();
             os.close();
          } catch (IOException e) {
              e.printStackTrace();
          }
     }
 }

并新建两个带有该类实例的线程:

    String pathname = "/home/sjtu123/test.arff";
    TrainSetBuildTask task1 = new TrainSetBuildTask(pathname);
    Thread t1 = new Thread(task1);
    TrainSetBuildTask task2 = new TrainSetBuildTask(pathname);
    Thread t2 = new Thread(task2);
    t1.start();
    t2.start();

然后我收到错误 OverlappingFileLockException。我想知道为什么会发生这种情况，因为我只在每个线程中锁定文件一次？如何修复我的代码？

Answer 1

您不能同时多次锁定同一个文件。您需要使用 java 锁定对象来确保一次只有一个线程尝试锁定文件，或者以其他方式协调线程等待直到没有其他线程正在锁定。

来自manual :

File locks are held on behalf of the entire Java virtual machine. They are not suitable for controlling access to a file by multiple threads within the same virtual machine.