[jira] [Commented] (ZOOKEEPER-1128) Recipe wrong for Lock process.

["Laxman (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-1128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13069444#comment-13069444 ] 

Laxman commented on ZOOKEEPER-1128:
-----------------------------------

While implementing the lock recipe, I interpreted "the next lowest sequence number" correctly. I feel this phrase is not ambiguous and don't need to correct it.

Any suggestions?

> 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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