ADDITIONAL SYSTEM INFORMATION :
macOS 10.13.4 using:

Java version "1.8.0_171"
Java(TM) SE Runtime Environment (build 1.8.0_171-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.171-b11, mixed mode)


A DESCRIPTION OF THE PROBLEM :
Taking a second lock on a ExFAT or MS-DOS (FAT) formatted disk using macOS 10.13.4 always results in a OverlappingFileLockException. If I use DiskUtily and format the drive to Mac OS Extended (Journaled) or Mac OS Extended (Case Sensitive, Journaled) I don't get this issue. If I plug the same drive into a Windows 10 machine I don't get the issue. It's just macOS with ExFAT or MS-DOS (FAT).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Using DiskUtility, format an external drive to ExFAT or MS-DOS (FAT). Update the filePath variable to be the root of your drive and run the attached program.


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Program to print:

filePath: /Volumes/SAMSUNG_T5/a/file.txt
Got lock: sun.nio.ch.FileLockImpl[0:9223372036854775807 exclusive valid]
filePath: /Volumes/SAMSUNG_T5/b/file.txt
Got lock: sun.nio.ch.FileLockImpl[0:9223372036854775807 exclusive valid]

ACTUAL -
Unable to take the second lock:

filePath: /Volumes/SAMSUNG_T5/a/file.txt
Got lock: sun.nio.ch.FileLockImpl[0:9223372036854775807 exclusive valid]
filePath: /Volumes/SAMSUNG_T5/b/file.txt
Exception in thread "main" java.nio.channels.OverlappingFileLockException
at sun.nio.ch.SharedFileLockTable.checkList(FileLockTable.java:255)
at sun.nio.ch.SharedFileLockTable.add(FileLockTable.java:152)
at sun.nio.ch.FileChannelImpl.tryLock(FileChannelImpl.java:1108)
at java.nio.channels.FileChannel.tryLock(FileChannel.java:1155)
at LockDemo.takeLock(LockDemo.java:35)
at LockDemo.main(LockDemo.java:25)


---------- BEGIN SOURCE ----------
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.file.Files;
import java.nio.file.Paths;

public class LockDemo
{

    public static void main(
        String[] args) throws IOException
    {
        final String filePath = "/Volumes/SAMSUNG_T5";
        final String a = filePath + File.separator + "a";
        final String b = filePath + File.separator + "b";
        
        Files.createDirectories(Paths.get(a));
        Files.createDirectories(Paths.get(b));

        takeLock(a);
        takeLock(b);
    }
    
    private static void takeLock(
        final String pathname) throws IOException
    {
        final String filePath = pathname + File.separator + "file.txt";
        System.out.println("filePath: " + filePath);
        final FileOutputStream os = new FileOutputStream(new File(filePath), true);
        final FileChannel channel = os.getChannel();
        FileLock lock = channel.tryLock();
        System.out.println("Got lock: " + lock);
    }
    
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None.

FREQUENCY : always