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Listener callback) {
this.callback = callback;
}
/**
* Removes the lock or associated znode if
* you no longer require the lock. this also
* removes your request in the queue for locking
* in case you do not already hold the lock.
* @throws RuntimeException throws a runtime exception
* if it cannot connect to zookeeper.
*/
public synchronized void unlock() throws RuntimeException {
if (!isClosed() && id != null) {
// we don't need to retry this operation in the case of failure
// as ZK will remove ephemeral files and we don't wanna hang
// this process when closing if we cannot reconnect to ZK
try {
ZooKeeperOperation zopdel = new ZooKeeperOperation() {
public boolean execute() throws KeeperException,
InterruptedException {
zookeeper.delete(id, -1);
return Boolean.TRUE;
}
};
zopdel.execute();
} catch (InterruptedException e) {
LOG.warn("Caught: " + e, e);
//set that we have been interrupted.
Thread.currentThread().interrupt();
} catch (KeeperException.NoNodeException e) {
// do nothing
} catch (KeeperException e) {
LOG.warn("Caught: " + e, e);
throw (RuntimeException) new RuntimeException(e.getMessage()).
initCause(e);
}
finally {
if (callback != null) {
callback.lockReleased();
}
id = null;
}
}
}
/**
* the watcher called on
* getting watch while watching
* my predecessor
*/
private class LockWatcher implements Watcher {
public void process(WatchedEvent event) {
// lets either become the leader or watch the new/updated node
LOG.debug("Watcher fired on path: " + event.getPath() + " state: " +
event.getState() + " type " + event.getType());
try {
lock();
} catch (Exception e) {
LOG.warn("Failed to acquire lock: " + e, e);
}
}
}
/**
* a zoookeeper operation that is mainly responsible
* for all the magic required for locking.
*/
private class LockZooKeeperOperation implements ZooKeeperOperation {
/** find if we have been created earler if not create our node
*
* @param prefix the prefix node
* @param zookeeper teh zookeeper client
* @param dir the dir paretn
* @throws KeeperException
* @throws InterruptedException
*/
private void findPrefixInChildren(String prefix, ZooKeeper zookeeper, String dir)
throws KeeperException, InterruptedException {
List<String> names = zookeeper.getChildren(dir, false);
for (String name : names) {
if (name.startsWith(prefix)) {
id = dir + "/" + name;
if (LOG.isDebugEnabled()) {
LOG.debug("Found id created last time: " + id);
}
break;
}
}
if (id == null) {
id = zookeeper.create(dir + "/" + prefix, data,
getAcl(), EPHEMERAL_SEQUENTIAL);
if (LOG.isDebugEnabled()) {
LOG.debug("Created id: " + id);
}
}
}
/**
* the command that is run and retried for actually
* obtaining the lock
* @return if the command was successful or not
*/
public boolean execute() throws KeeperException, InterruptedException {
do {
if (id == null) {
long sessionId = zookeeper.getSessionId();
String prefix = "x-" + sessionId + "-";
// lets try look up the current ID if we failed
// in the middle of creating the znode
findPrefixInChildren(prefix, zookeeper, dir);
idName = new ZNodeName(id);
}
if (id != null) {
List<String> names = zookeeper.getChildren(dir, false); |