[ZOOKEEPER-1128] Recipe wrong for Lock process.

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.3.3
• Component/s: recipes
• Assignee: yynil
• Reporter: yynil
• Created: 19/Jul/11 16:49
• Updated: 03/Mar/16 01:35
• Resolved: 28/Jul/11 01:21

Description

http://zookeeper.apache.org/doc/trunk/recipes.html
The current recipe for Lock has the wrong process.
Specifically, for the
"4. The client calls exists( ) with the watch flag set on the path in the lock directory with the next lowest sequence number."
It shouldn't be the "the next lowest sequence number". It should be the "current lowest path".

If you're gonna use "the next lowest sequence number", you'll never wait for the lock possession.

The following is the test code:

LockTest.java

        ACL acl = new ACL(Perms.ALL, new Id("10.0.0.0/8", "1"));
        List<ACL> acls = new ArrayList<ACL>();
        acls.add(acl);
        String connectStr = "localhost:2181";
        final Semaphore sem = new Semaphore(0);
        ZooKeeper zooKeeper = new ZooKeeper(connectStr, 1000 * 30, new Watcher() {

            @Override
            public void process(WatchedEvent event) {
                System.out.println("eventType:" + event.getType());
                System.out.println("keeperState:" + event.getState());
                if (event.getType() == Event.EventType.None) {
                    if (event.getState() == Event.KeeperState.SyncConnected) {
                        sem.release();
                    }
                }
            }
        });
        System.out.println("state:" + zooKeeper.getState());
        System.out.println("Waiting for the state to be connected");
        try {
            sem.acquire();
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
        System.out.println("Now state:" + zooKeeper.getState());

        String directory = "/_locknode_";
        Stat stat = zooKeeper.exists(directory, false);
        if (stat == null) {
            zooKeeper.create(directory, new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        }
        String prefix = directory + "/lock-";
        String path = zooKeeper.create(prefix, new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println("Create the path for " + path);
        while (true) {
            List<String> children = zooKeeper.getChildren(directory, false);
            Collections.sort(children);
            System.out.println("The whole lock size is " + children.size());
            String lowestPath = children.get(0);
            DecimalFormat df = new DecimalFormat("0000000000");
            String currentSuffix = lowestPath.substring("lock-".length());
            System.out.println("CurrentSuffix is " + currentSuffix);
            int intIndex = Integer.parseInt(currentSuffix);

            if (path.equals(directory + "/" + lowestPath)) {
                //I've got the lock and release it
                System.out.println("I've got the lock at " + new Date());
                System.out.println("next index is " + intIndex);
                Thread.sleep(10000);
                System.out.println("After sleep 3 seconds, I'm gonna release the lock");
                zooKeeper.delete(path, -1);
                break;
            }
            final Semaphore wakeupSem = new Semaphore(0);
            stat = zooKeeper.exists(directory + "/" + lowestPath, new Watcher() {

                @Override
                public void process(WatchedEvent event) {
                    System.out.println("Event is " + event.getType());
                    System.out.println("State is " + event.getState());
                    if (event.getType() == Event.EventType.NodeDeleted) {
                        wakeupSem.release();
                    }
                }
            });
            if (stat != null) {
                System.out.println("Waiting for the delete of ");
                wakeupSem.acquire();
            } else {
                System.out.println("Continue to seek");
            }
        }