Package org.jgroups.protocols

Class CENTRAL_LOCK

java.lang.Object

org.jgroups.stack.Protocol

org.jgroups.protocols.Locking

org.jgroups.protocols.CENTRAL_LOCK

All Implemented Interfaces:

LockNotification

public class CENTRAL_LOCK
extends Locking
implements LockNotification

Implementation of a locking protocol which acquires locks by contacting the coordinator.

Because the coordinator maintains all locks, no total order configuration is required.

CENTRAL_LOCK has all members send lock and unlock requests to a central coordinator. The coordinator has a queue for incoming requests, and grants locks based on order of arrival. To prevent all acquired locks from being forgotten when the coordinator crashes, setting num_backups lets the coordinator backup lock information to a number of backup nodes. Valid values for num_backups are 0 (no backup) to N-1, e.g. in a cluster of 4, we can have only 3 backup nodes.

Say we have a cluster of {A,B,C,D,E} and num_backups=1. A is the coordinator, and A updates all locks (and released locks) in B as well. When A crashes, everybody falls over to B for sending lock and unlock requests. B in turn copies all existing locks over to C and - when locks are acquired or released - forwards this information to C as well.

An alternative is also the PEER_LOCK protocol.

Since:

2.12

Author:

Bela Ban

See Also:

• Locking
• PEER_LOCK

Nested Class Summary

Nested classes/interfaces inherited from class org.jgroups.protocols.Locking

Locking.ClientCondition, Locking.ClientLock, Locking.LockingHeader, Locking.Request, Locking.ServerCondition, Locking.ServerLock, Locking.Type

Field Summary

Fields

Modifier and Type	Field	Description
protected final List<Address>	backups
protected Address	coord
protected boolean	is_coord
protected int	num_backups

Fields inherited from class org.jgroups.protocols.Locking

bypass_bundling, client_locks, local_addr, lock_listeners, server_locks, view

Fields inherited from class org.jgroups.stack.Protocol

down_prot, ergonomics, id, log, name, stack, stats, up_prot

Constructor Summary

Constructors

Constructor	Description
CENTRAL_LOCK()

Method Summary

Modifier and Type	Method	Description
void	awaited(String lock_name, Owner owner)
void	awaiting(String lock_name, Owner owner)
protected void	copyLocksTo(List<Address> new_joiners)
String	getBackups()
Address	getCoord()
String	getCoordinator()
int	getNumberOfBackups()
void	handleView(View view)
boolean	isCoord()
void	lockCreated(String name)
void	lockDeleted(String name)
void	locked(String lock_name, Owner owner)
protected void	sendAwaitConditionRequest(String lock_name, Owner owner)
protected void	sendCreateLockRequest(Address dest, String lock_name, Owner owner)
protected void	sendDeleteAwaitConditionRequest(String lock_name, Owner owner)
protected void	sendDeleteLockRequest(Address dest, String lock_name)
protected void	sendGrantLockRequest(String lock_name, Owner owner, long timeout, boolean is_trylock)
protected void	sendReleaseLockRequest(String lock_name, Owner owner)
protected void	sendSignalConditionRequest(String lock_name, boolean all)
void	setNumberOfBackups(int num_backups)
void	unlocked(String lock_name, Owner owner)
protected void	updateBackups(Locking.Type type, String lock_name, Owner owner)

Methods inherited from class org.jgroups.protocols.Locking

addLockListener, createLock, down, getAddress, getBypassBundling, getLock, getLock, getLock, getOwner, getView, handleAwaitRequest, handleCreateAwaitingRequest, handleCreateLockRequest, handleDeleteAwaitingRequest, handleDeleteAwaitRequest, handleDeleteLockRequest, handleLockDeniedResponse, handleLockGrantedResponse, handleLockRequest, handleSignalRequest, handleSignalResponse, notifyAwaited, notifyAwaiting, notifyLockCreated, notifyLockDeleted, notifyLocked, notifyUnlocked, printLocks, removeClientLock, removeLockListener, sendLockResponse, sendRequest, sendSignalResponse, setBypassBundling, unlockAll, up

Methods inherited from class org.jgroups.stack.Protocol

destroy, downThreadEnabled, dumpStats, enableStats, getConfigurableObjects, getDownProtocol, getId, getLevel, getName, getProperties, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getValue, init, isErgonomics, printStats, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, resetStats, setDownProtocol, setErgonomics, setId, setLevel, setProperties, setPropertiesInternal, setProperty, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, start, statsEnabled, stop, upThreadEnabled

Methods inherited from class java.lang.Object

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

Field Details

num_backups

protected int num_backups

coord

protected Address coord

is_coord

protected boolean is_coord

backups

protected final List<Address> backups

Constructor Details

CENTRAL_LOCK

public CENTRAL_LOCK()

Method Details

getCoord

public Address getCoord()

isCoord

public boolean isCoord()

getCoordinator

public String getCoordinator()

getNumberOfBackups

public int getNumberOfBackups()

setNumberOfBackups

public void setNumberOfBackups(int num_backups)

getBackups

public String getBackups()

sendGrantLockRequest

protected void sendGrantLockRequest(String lock_name,
 Owner owner,
 long timeout,
 boolean is_trylock)

Specified by:

sendGrantLockRequest in class Locking

sendReleaseLockRequest

protected void sendReleaseLockRequest(String lock_name,
 Owner owner)

Specified by:

sendReleaseLockRequest in class Locking

sendCreateLockRequest

protected void sendCreateLockRequest(Address dest,
 String lock_name,
 Owner owner)

sendDeleteLockRequest

protected void sendDeleteLockRequest(Address dest,
 String lock_name)

sendAwaitConditionRequest

protected void sendAwaitConditionRequest(String lock_name,
 Owner owner)

Specified by:

sendAwaitConditionRequest in class Locking

sendSignalConditionRequest

protected void sendSignalConditionRequest(String lock_name,
 boolean all)

Specified by:

sendSignalConditionRequest in class Locking

sendDeleteAwaitConditionRequest

protected void sendDeleteAwaitConditionRequest(String lock_name,
 Owner owner)

Specified by:

sendDeleteAwaitConditionRequest in class Locking

handleView

public void handleView(View view)

Overrides:

handleView in class Locking

lockCreated

public void lockCreated(String name)

Specified by:

lockCreated in interface LockNotification

lockDeleted

public void lockDeleted(String name)

Specified by:

lockDeleted in interface LockNotification

locked

public void locked(String lock_name,
 Owner owner)

Specified by:

locked in interface LockNotification

unlocked

public void unlocked(String lock_name,
 Owner owner)

Specified by:

unlocked in interface LockNotification

awaiting

public void awaiting(String lock_name,
 Owner owner)

Specified by:

awaiting in interface LockNotification

awaited

public void awaited(String lock_name,
 Owner owner)

Specified by:

awaited in interface LockNotification

updateBackups

protected void updateBackups(Locking.Type type,
 String lock_name,
 Owner owner)

copyLocksTo

protected void copyLocksTo(List<Address> new_joiners)