Lock file/"folder" to a specific JVM and iterate if locked

Question

I'm using multiple JVMs, but I need that each JVM to use a specific folder. What I'm trying to do is iterate through folders till it finds a file that is not locked and then lock it to use that specific folder.

Here I'm filtering the folders I want to use:

  // Filter 'fran' folders
  String dir = System.getProperty("user.dir");
  FilenameFilter filter = new FilenameFilter() {
     public boolean accept(File dir, String name) {
        String lowercaseName = name.toLowerCase();
        if (lowercaseName.startsWith("fran")) {
           return true;
        } else {
           return false;
        }
     }
  };
  File[] dirs = new File(dir).listFiles(filter);

Then I'm trying to go through the folders and check if it is locked or not with f.canWrite(). However it always appears to use only one folder and ignore the others.

  // Find available folder
  boolean lock = true;
  String lock_folder = "";
  FileChannel fileChannel = null;
  FileLock lockfile = null;
  File f = null;

  while (lock) {
     for (File folder : dirs) {
        f = new File(folder + "\\lock.txt");
        Boolean isnotlocked = f.canWrite();
        if (isnotlocked) {
           fileChannel = new RandomAccessFile(f, "rw").getChannel();
           lockfile = fileChannel.lock();
           lock = false;
           lock_folder = folder.getAbsolutePath();
           break;
        }
     }
  }

I+ve previously tried to accomplish what I needed without FileLock, creating a file in the specific folder and then deleting after completed. If the folder did not have that file it would create and lock that JVM. However I think the JVMs were getting mixed cause the results were bad.

Hope u can understand what my problem is, would really appreciate some help.

Answer 1

Here are some ideas:

Assuming a process class - CustomProcess.java. This runs in a separate thread. The class has a constructor which takes a file folder as an argument. Lets assume the filePath1 is the folder's path and is accepted from a FileChooser.

(a) How the application works:

Put the selected folder filePath1 in a collection like List<File> or List<Path> - lets call it processFilesList; this is shared (perhaps a static member) by all the processes (this needs to be a concurrent collection from java.util.concurrent package). This list tracks the folders which are already being processed. Before the process starts check if the filePath1 is already in the processFilesList.

(b) Create and start the process:

CustomProcess p1 = new CustomProcess(filePath1);
p1.startProcess(); // here the application does whatever with the files in the folder.

Option 2:

Put all the folder file paths that need to be processed in a Queue collection. Process each folder (and its files as needed) one at a time or by multiple processes. The queue can be a first-in-first-out (FIFO) or a last-in-first-out (LIFO). One can consider these concurrent queue implementations based on the requirement: ConcurrentLinkedQueue, LinkedBlockingQueue, ConcurrentLinkedDeque or LinkedBlockingDeque.