public static void main(String args[]) throws IOException {
if (args.length != 1) {
System.err.println("Usage: java LockingExample <input file>");
System.exit(0);
}
FileLock sharedLock = null;
FileLock exclusiveLock = null;
try {
RandomAccessFile raf = new RandomAccessFile(args[0], "rw");
// get the channel for the file
FileChannel channel = raf.getChannel();
System.out.println("trying to acquire lock ...");
// this locks the first half of the file - exclusive
exclusiveLock = channel.lock(0, raf.length() / 2, SHARED);
System.out.println("lock acquired ...");
/** Now modify the data . . . */
try {
// sleep for 10 seconds
Thread.sleep(10000);
} catch (InterruptedException ie) {
}
// release the lock
exclusiveLock.release();
System.out.println("lock released ...");
// this locks the second half of the file - shared
sharedLock = channel.lock(raf.length() / 2 + 1, raf.length(), SHARED);
/** Now read the data . . . */
// release the lock
sharedLock.release();
} catch (java.io.IOException ioe) {
System.err.println(ioe);
} finally {
if (exclusiveLock != null) exclusiveLock.release();
if (sharedLock != null) sharedLock.release();
}
}
public void run() {
try {
// Exclusive lock with no overlap:
FileLock fl = fc.lock(start, end, false);
System.out.println("Locked: " + start + " to " + end);
// Perform modification:
while (buff.position() < buff.limit() - 1) buff.put((byte) (buff.get() + 1));
fl.release();
System.out.println("Released: " + start + " to " + end);
} catch (IOException e) {
throw new RuntimeException(e);
}
}