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 .