org.apache.zookeeper.recipes.lock

Class WriteLock

java.lang.Object

org.apache.zookeeper.recipes.lock.WriteLock

public class WriteLock
extends Object

A protocol to implement an exclusive write lock or to elect a leader.

You invoke lock() to start the process of grabbing the lock; you may get the lock then or it may be some time later.

You can register a listener so that you are invoked when you get the lock; otherwise you can ask if you have the lock by calling isOwner()

Field Summary

Fields

Modifier and Type	Field and Description
protected org.apache.zookeeper.ZooKeeper	zookeeper

Constructor Summary

Constructors

Constructor and Description
WriteLock(org.apache.zookeeper.ZooKeeper zookeeper, String dir, List<org.apache.zookeeper.data.ACL> acl) zookeeper contructor for writelock
WriteLock(org.apache.zookeeper.ZooKeeper zookeeper, String dir, List<org.apache.zookeeper.data.ACL> acl, LockListener callback) zookeeper contructor for writelock with callback

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes this strategy and releases any ZooKeeper resources; but keeps the ZooKeeper instance open
protected void	doClose() Allow derived classes to perform some custom closing operations to release resources
protected void	ensureExists(String path, byte[] data, List<org.apache.zookeeper.data.ACL> acl, org.apache.zookeeper.CreateMode flags) Ensures that the given path exists with the given data, ACL and flags
protected void	ensurePathExists(String path) Ensures that the given path exists with no data, the current ACL and no flags
List<org.apache.zookeeper.data.ACL>	getAcl() return the acl its using
String	getDir() return the parent dir for lock
String	getId() return the id for this lock
LockListener	getLockListener() return the current locklistener
long	getRetryDelay() get the retry delay in milliseconds
org.apache.zookeeper.ZooKeeper	getZookeeper() return zookeeper client instance
protected boolean	isClosed() Returns true if this protocol has been closed
boolean	isOwner() Returns true if this node is the owner of the lock (or the leader)
boolean	lock() Attempts to acquire the exclusive write lock returning whether or not it was acquired.
protected void	retryDelay(int attemptCount) Performs a retry delay if this is not the first attempt
protected Object	retryOperation(ZooKeeperOperation operation) Perform the given operation, retrying if the connection fails
void	setAcl(List<org.apache.zookeeper.data.ACL> acl) set the acl
void	setLockListener(LockListener callback) register a different call back listener
void	setRetryDelay(long retryDelay) Sets the time waited between retry delays
void	unlock() Removes the lock or associated znode if you no longer require the lock.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

zookeeper

protected final org.apache.zookeeper.ZooKeeper zookeeper

Constructor Detail

WriteLock

public WriteLock(org.apache.zookeeper.ZooKeeper zookeeper,
         String dir,
         List<org.apache.zookeeper.data.ACL> acl)

zookeeper contructor for writelock

Parameters:

zookeeper - zookeeper client instance

dir - the parent path you want to use for locking

acls - the acls that you want to use for all the paths, if null world read/write is used.

WriteLock

public WriteLock(org.apache.zookeeper.ZooKeeper zookeeper,
         String dir,
         List<org.apache.zookeeper.data.ACL> acl,
         LockListener callback)

zookeeper contructor for writelock with callback

Parameters:

zookeeper - the zookeeper client instance

dir - the parent path you want to use for locking

acl - the acls that you want to use for all the paths

callback - the call back instance

Method Detail

getLockListener

public LockListener getLockListener()

return the current locklistener

Returns:

the locklistener

setLockListener

public void setLockListener(LockListener callback)

register a different call back listener

Parameters:

callback - the call back instance

unlock

public void unlock()
            throws RuntimeException

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.

lock

public boolean lock()
             throws org.apache.zookeeper.KeeperException,
                    InterruptedException

Attempts to acquire the exclusive write lock returning whether or not it was acquired. Note that the exclusive lock may be acquired some time later after this method has been invoked due to the current lock owner going away.

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

getDir

public String getDir()

return the parent dir for lock

Returns:

the parent dir used for locks.

isOwner

public boolean isOwner()

Returns true if this node is the owner of the lock (or the leader)

getId

public String getId()

return the id for this lock

Returns:

the id for this lock

close

public void close()

Closes this strategy and releases any ZooKeeper resources; but keeps the ZooKeeper instance open

getZookeeper

public org.apache.zookeeper.ZooKeeper getZookeeper()

return zookeeper client instance

Returns:

zookeeper client instance

getAcl

public List<org.apache.zookeeper.data.ACL> getAcl()

return the acl its using

Returns:

the acl.

setAcl

public void setAcl(List<org.apache.zookeeper.data.ACL> acl)

set the acl

Parameters:

acl - the acl to set to

getRetryDelay

public long getRetryDelay()

get the retry delay in milliseconds

Returns:

the retry delay

setRetryDelay

public void setRetryDelay(long retryDelay)

Sets the time waited between retry delays

Parameters:

retryDelay - the retry delay

doClose

protected void doClose()

Allow derived classes to perform some custom closing operations to release resources

retryOperation

protected Object retryOperation(ZooKeeperOperation operation)
                         throws org.apache.zookeeper.KeeperException,
                                InterruptedException

Perform the given operation, retrying if the connection fails

Returns:

object. it needs to be cast to the callee's expected return type.

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

ensurePathExists

protected void ensurePathExists(String path)

Ensures that the given path exists with no data, the current ACL and no flags

Parameters:

path -

ensureExists

protected void ensureExists(String path,
                byte[] data,
                List<org.apache.zookeeper.data.ACL> acl,
                org.apache.zookeeper.CreateMode flags)

Ensures that the given path exists with the given data, ACL and flags

Parameters:

path -

acl -

flags -

isClosed

protected boolean isClosed()

Returns true if this protocol has been closed

Returns:

true if this protocol is closed

retryDelay

protected void retryDelay(int attemptCount)

Performs a retry delay if this is not the first attempt

Parameters:

attemptCount - the number of the attempts performed so far