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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