How to check FileLock without truncating file?

Question

I recently added filelocks to my downloader asynctask:

FileOutputStream file = new FileOutputStream(_outFile);
file.getChannel().lock();

and after download completes, file.close() to release lock.

From a called BroadcastReceiver (different thread), I need to go through the files and see which are downloaded and which are still locked. I started with trylock:

for (int i=0; i<files.length; i++) {
    try {
        System.out.print((files[i]).getName());
        test = new FileOutputStream(files[i]);
        FileLock lock = test.getChannel().tryLock();
        if (lock != null) {
            lock.release();
            //Not a partial download. Do stuff.
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        test.close();
    }
}

Unfortunately I read the file is truncated (0 bytes) when the FileOutputStream is created. I set it to append, but the lock doesn't seem to take effect, all appear to be un-locked (fully downloaded)

Is there another way to check if a write-lock is applied to the file currently, or am I using the wrong methods here? Also, is there a way to debug file-locks, from the ADB terminal or Eclipse?

Answer 1

None of this is going to work. Check the Javadoc. Locks are held on behalf of the entire process, i.e. the JVM, not by individual threads.

Answer 2

My first thought would be to open it for append per the javadocs

test = new FileOutputStream(files[i], true); // the true specifies for append