File.exists() is not accurate on smb2 network share (use WatchService?)

Question

Hi,
According to this document: SMB2 Client Redirector Caches Explained File.exists() is not accurate on a smb2 network share. I am not able to change any register settings, so I want to deal with it. According to the document there is an API to get the notifications from the file system. I assumed that the WatchService is the Java implementation of this API. Am I correct?
I started with the WatchDir example from the jdk samples and stripped it a bit. I only need to know when a file is created and delete (I don't care about file modifications). For testing I have added new File.exists() when a new event has been triggered. I also start a separated Thread which test the file existence also. When I don't start this separated thread the file exists returns true immediately. When the extra thread is started it is not accurate any more. I need a more accurate file.exists check in the whole application and all running threads.
The output for my test case is this:
FileExistsThread: subdir\test.txt == false
watch registered for dir: subdir\
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
WatchDir event: ENTRY_CREATE: test.txt
WatchDir: subdir\test.txt exists == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == false
FileExistsThread: subdir\test.txt == true
FileExistsThread: subdir\test.txt == true
FileExistsThread: subdir\test.txt == true
FileExistsThread: subdir\test.txt == true
As you can see the file test.txt  is created on line 9. The FileExistsThread have seen it on line 20, (at least 10 x 300 ms later).
For testing I have used 2 Windows 7 pc's (with smb2 enabled which is default). The working directory must be on the remote pc and the file test.txt must be created (or copied from another folder) on the remote pc (not using the network drive, but on the pc itself).
Here is my test code:
package nl.test.main;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import java.io.File;
import java.io.IOException;
import java.nio.file.ClosedWatchServiceException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
public class WatchDir
  private final WatchService _watcher;
  private final String _dir;
  public WatchDir( String dir ) throws IOException
    _dir = dir;
    _watcher = FileSystems.getDefault().newWatchService();
    Paths.get( dir ).register( _watcher, ENTRY_CREATE, ENTRY_DELETE );
    System.out.println( "watch registered for dir: " + dir );
  public void run()
    try
      while ( true )
        WatchKey key = _watcher.take();
        for ( WatchEvent<?> event : key.pollEvents() )
          WatchEvent.Kind<?> kind = event.kind();
          if ( kind == OVERFLOW )
            continue;
          @SuppressWarnings( "unchecked" )
          WatchEvent<Path> ev = (WatchEvent<Path>)event;
          Path fileName = ev.context();
          System.out.println( "WatchDir event: " + kind.name() + ": " + fileName );
          if ( kind == ENTRY_CREATE )
            String realPath = _dir + fileName;
            System.out.println( "WatchDir: " + realPath + " exists == " + new File( realPath ).exists() );
        key.reset();
    catch ( ClosedWatchServiceException x )
      return;
    catch ( InterruptedException ex )
      return;
  public static void main( String[] args )
    Thread t = new Thread( new Runnable()
      @Override
      public void run()
        try
          while ( true )
            String filename = "subdir\\test.txt";
            boolean fileExists = new File( filename ).exists();
            System.err.println( "FileExistsThread: " + filename + " == " + fileExists );
            Thread.sleep( 300 );
        catch ( InterruptedException e )
          e.printStackTrace();
          return;
    t.start();
    try
      new WatchDir( "subdir\\" ).run();
    catch ( IOException e )
      e.printStackTrace();
Any idea's?
Thanks,
Olaf

Answer 1

If you donot have access to note 45172.1 as specified by Laurent Schneider.
Snippet from note
a. Mapped Drive : To use a mapped drive, the user that the service starts as
must have setup a drive to match UTL_FILE_DIR and be logged onto the server
when UTL_FILE is in use.
b. Universal Naming Convention : UNC is preferable to Mapped Drives because
it does not require anyone to be logged on and UTL_FILE_DIR should be set to
a name in the form :
\\\<machine name>\<share name>\<path>
or
"\\<machine name>\<share name>\<path>"