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  1. JDK
  2. JDK-8167023

(ch) Support locking of SMB/AFP network files on OS X



    • Type: Enhancement
    • Status: Open
    • Priority: P4
    • Resolution: Unresolved
    • Affects Version/s: 8u102, 9
    • Fix Version/s: tbd
    • Component/s: core-libs
    • Environment:

      OS X 10.10.5 with mounted network shares via either AFP or SMB.
      Fails on other versions of OS X as well.


      When trying to lock a file that is on a SMB or an AFP network filesystem, FileChannel.tryLock() throws an IOException with the message "Operation not supported" .

      The reason seems to be that the JRE uses the call fcntl to try to lock files on these network shares. On OS X fcntl does not support locking files on AFP or SMB (I believe NFS works alright, but am not certain). A possible alternative is perhaps the call flock for AFP and SMB.

      More general information can be found on http://www.briandwells.com/main/Blog/Entries/2006/10/5_Subversion,_Mac_OS_X,_and_SMB.html

      To test the problem, mount an SMB or AFP share on a OS X machine. Then run this code with one of the mounted files as argument:

      import java.io.*;
      import java.nio.channels.FileChannel;
      import java.nio.channels.FileLock;

      public class FileLockTest {

          public static void main(String[] args) throws Exception {
              RandomAccessFile file = null;
              FileLock fileLock = null;
                  file = new RandomAccessFile(args[0], "rw");
                  FileChannel fileChannel = file.getChannel();

                  fileLock = fileChannel.tryLock();
                  if (fileLock != null){
                      System.out.println("File is locked");
              } finally{
                  if (fileLock != null){

      When working properly, you should see the text "File is locked".
      When failing, you see something like:

      Exception in thread "main" java.io.IOException: Operation not supported
          at sun.nio.ch.FileDispatcherImpl.lock0(Native Method)
          at sun.nio.ch.FileDispatcherImpl.lock(FileDispatcherImpl.java:90)
          at sun.nio.ch.FileChannelImpl.tryLock(FileChannelImpl.java:1114)
          at java.nio.channels.FileChannel.tryLock(FileChannel.java:1155)
          at FileLockTest.main(FileLockTest.java:15)

      Please note that the thrown exception is not very helpful, because it is a plain IOException with some message. As a programmer, I'd like to distinguish between a real failure or an unsupported operation. Even if for some reason proper locking cannot be implemented, please implement a specific exception that is thrown in case a file cannot be locked, because the mechanism isn't properly implemented or supported by the OS. Something like FileLockUnsupportedException (subclass of IOException) with a proper reason that perhaps contains the filesystem type.




            bpb Brian Burkhalter
            hschreiber Hendrik Schreiber
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