NativeFSLockFactory (Lucene 10.5.1 core API)
Description: declaration: package: org.apache.lucene.store, class: NativeFSLockFactory

Package org.apache.lucene.store

# Class NativeFSLockFactory

java.lang.Object
org.apache.lucene.store.LockFactory
org.apache.lucene.store.FSLockFactory
org.apache.lucene.store.NativeFSLockFactory

public final class NativeFSLockFactory extends FSLockFactory
Implements `LockFactory` using native OS file locks. Note that because this LockFactory relies on java.nio.* APIs for locking, any problems with those APIs will cause locking to fail. Specifically, on certain NFS environments the java.nio.* locks will fail (the lock can incorrectly be double acquired) whereas `SimpleFSLockFactory` worked perfectly in those same environments. For NFS based access to an index, it's recommended that you try `SimpleFSLockFactory` first and work around the one limitation that a lock file could be left when the JVM exits abnormally.

The primary benefit of `NativeFSLockFactory` is that locks (not the lock file itself) will be properly removed (by the OS) if the JVM has an abnormal exit.

Note that, unlike `SimpleFSLockFactory`, the existence of leftover lock files in the filesystem is fine because the OS will free the locks held against these files even though the files still remain. Lucene will never actively remove the lock files, so although you see them, the index may not be locked.

Special care needs to be taken if you change the locking implementation: First be certain that no writer is in fact writing to the index otherwise you can easily corrupt your index. Be sure to do the LockFactory change on all Lucene instances and clean up all leftover lock files before starting the new configuration for the first time. Different implementations can not work together!

If you suspect that this or any other LockFactory is not working properly in your environment, you can easily test it by using `VerifyingLockFactory`, `LockVerifyServer` and `LockStressTest`.

This is a singleton, you have to use `INSTANCE`.

See Also:
  - `LockFactory`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final NativeFSLockFactory`
  `INSTANCE`
  Singleton instance

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected Lock`
  `obtainFSLock(FSDirectory dir, String lockName)`
  Implement this method to obtain a lock for a FSDirectory instance.

  ### Methods inherited from class org.apache.lucene.store.FSLockFactory

  `getDefault, obtainLock`

  ### Methods inherited from class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### INSTANCE

    public static final NativeFSLockFactory INSTANCE
    Singleton instance

- ## Method Details

  - ### obtainFSLock

    protected Lock obtainFSLock(FSDirectory dir, String lockName) throws IOException
    Description copied from class: `FSLockFactory`
    Implement this method to obtain a lock for a FSDirectory instance.
    Specified by:
      `obtainFSLock` in class `FSLockFactory`
    Throws:
      `IOException` - if the lock could not be obtained.