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https://issues.apache.org/jira/browse/ZOOKEEPER-1128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13072135#comment-13072135
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yynil commented on ZOOKEEPER-1128:
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ops, I got it.
I just misunderstood the term "the next lowest sequence number".
It means "next" to MY number while is not "next" to the current lock number.
It solves my problem and it's way better than "current lock" solution I'm using
now.
But some more suggestion is to just add your comments here in the tutorial. I
don't know if I'm the only one to misunderstand it.
> Recipe wrong for Lock process.
> ------------------------------
>
> Key: ZOOKEEPER-1128
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1128
> Project: ZooKeeper
> Issue Type: Bug
> Components: recipes
> Affects Versions: 3.3.3
> Reporter: yynil
>
> 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:
> {code:title=LockTest.java|borderStyle=solid}
> 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");
> }
> }
> {code}
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