FileLock problem

Question

I'm new to the NIO API, so this may be a silly misuse of it (I did search the forums for an answer here but didn't find one). What's wrong with the following code snippet?
public class TestFileLock {
    public static void main(String[] args) {
        try {          
           FileOutputStream fos = new FileOutputStream("c:\\foo.txt");
           FileLock lock = fos.getChannel().lock();            
           FileInputStream fis = new FileInputStream("c:\\foo.txt");             
           while (fis.read() != -1) {                   
       catch (Exception e) {
           System.err.println(e.getMessage());
}When the call to fis.read() is executed, the catch block is always entered and the error message printed is:
"The process cannot access the file because another process has locked a portion of the file"
But this is all in a single instance of the JVM i.e. there is only one process. Is there something I'm missing about the use of FileLock objects and the mixing of Input and Output streams?

Answer 1

Hmmm, well, I was trying to write some code that would gain exclusive access to a file such that no other VMs could access the file until I was done with it (each of the VMs would go through the same set of locking code, so they would follow the same protocol - attempt to gain an exclusive lock on the shared file and then perform a set of read/write operations on the file once the lock had been obtained). I thought I could lock the file and then perform an arbitrary set of read/write operations on it within the VM that obtained the lock until the lock was released. Doesn't look like that's possible using this methodology. Is there any other way to accomplish this? I guess what I'm really looking for is some cross-VM synchronization that doesn't rely on creating a temporary file, since that is a bit unreliable.