org.adroitlogic.x.clustering.locks

Class ClusterLock

java.lang.Object

org.adroitlogic.x.clustering.locks.ClusterLock

All Implemented Interfaces:

XClusterLock, org.apache.curator.framework.state.ConnectionStateListener

public class ClusterLock
extends Object
implements XClusterLock, org.apache.curator.framework.state.ConnectionStateListener

Distributed Lock implementation of the Cluster manager. This is a non-reentrant lock. Whoever acquires this lock has to release this lock before being acquired again by the same or another thread

Since:

17.01

Author:

Imesha Sudasingha

Constructor Summary

Constructors

Constructor and Description
ClusterLock(org.apache.curator.framework.CuratorFramework client, String lockPath) Constructs a cluster lock instance.

Method Summary

Modifier and Type	Method and Description
void	acquire() Acquires the cluster lock.
boolean	acquire(long time, TimeUnit timeUnit) Acquire the lock - blocks until it's available or the given time expires.
String	getLockPath() Get the path used for acquiring the distributed lock.
org.apache.curator.framework.recipes.locks.InterProcessSemaphoreMutex	getUnderlyingLock()
boolean	isAcquiredInThisProcess() Whether this lock is acquired by a thread in this process.
void	release() Perform one release of the mutex if the calling thread is the same thread that acquired it.
void	stateChanged(org.apache.curator.framework.CuratorFramework client, org.apache.curator.framework.state.ConnectionState newState) State changes will be notified to this method.
boolean	tryAcquire() Tries to acquire the lock when called.

Methods inherited from class java.lang.Object

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

Constructor Detail

ClusterLock

public ClusterLock(org.apache.curator.framework.CuratorFramework client,
                   String lockPath)

Constructs a cluster lock instance. In the same time the lock will be added as an connection state listener in the curator client on order to listen to state changes in the connection to zookeeper

Parameters:

client - CuratorFramework client

lockPath - the path on which the lock will be acquired

Method Detail

acquire

public void acquire()
             throws Exception

Acquires the cluster lock. This is a blocking call, where the call will wait till the lock is acquired. Acquires the distributed lock by the calling thread. Made synchronize in order to make sure that this lock will not be acquired by the two threads of the same JVM at a given time.

Specified by:

acquire in interface XClusterLock

Throws:

Exception - in connection interruptions and underlying distributed coordination provider's errors

tryAcquire

public boolean tryAcquire()
                   throws Exception

Tries to acquire the lock when called. If unable to acquire the lock, returns immediately without blocking

Specified by:

tryAcquire in interface XClusterLock

Returns:

true, if the lock was acquired.

Throws:

Exception - in zookeeper errors and connection errors

acquire

public boolean acquire(long time,
                       TimeUnit timeUnit)
                throws Exception

Acquire the lock - blocks until it's available or the given time expires. Made synchronized in order to avoid 2 threads(of the same process) acquiring the same lock at given instance.

Specified by:

acquire in interface XClusterLock

Parameters:

time - time to wait

timeUnit - time unit

Returns:

true if succeeded

Throws:

Exception - connection interruptions

release

public void release()
             throws Exception

Perform one release of the mutex if the calling thread is the same thread that acquired it. If the thread had made multiple calls to acquire, the mutex will still be held when this method returns.

This method is not synchronized to avoid dead locks. That is, if a thread is waiting to acquire the lock in acquire() method, if this method was synchronized, even the owning thread cannot release the lock.

We have an edge case where the distributed lock is being acquired by a thread, another thread can call this method and release the lock. Developers has to be careful on this situation. No thread level lock is being used at the moment as we have requirements to release this lock by other threads.

Specified by:

release in interface XClusterLock

Throws:

Exception - interruptions, current thread does not own the lock

UnreliableLockException - if the connection was lost/session expired while the lock was acquired and before being released

isAcquiredInThisProcess

public boolean isAcquiredInThisProcess()

Whether this lock is acquired by a thread in this process.

Specified by:

isAcquiredInThisProcess in interface XClusterLock

Returns:

true is the lock is acquired by this process

getLockPath

public String getLockPath()

Get the path used for acquiring the distributed lock.

Specified by:

getLockPath in interface XClusterLock

Returns:

the path used to create the distributed lock

getUnderlyingLock

public org.apache.curator.framework.recipes.locks.InterProcessSemaphoreMutex getUnderlyingLock()

stateChanged

public void stateChanged(org.apache.curator.framework.CuratorFramework client,
                         org.apache.curator.framework.state.ConnectionState newState)

State changes will be notified to this method. If this lock is acquired by a thread in this process and if the connection state changes to ConnectionState.LOST, we cannot guarantee the reliability of the lock unless we receive a subsequent ConnectionState.RECONNECTED.

Specified by:

stateChanged in interface org.apache.curator.framework.state.ConnectionStateListener

Parameters:

client - curator client

newState - new connection state