GemFire 5.5

com.gemstone.gemfire.distributed
Class DistributedLockService

java.lang.Object
  extended by com.gemstone.gemfire.distributed.DistributedLockService

public abstract class DistributedLockService
extends Object

A named instance of DistributedLockService defines a space for locking arbitrary names across the distributed system defined by a specified distribution manager. Any number of DistributedLockService instances can be created with different service names. For all processes in the distributed system that have created an instance of DistributedLockService with the same name, no more than one thread is permitted to own the lock on a given name in that instance at any point in time. Additionally, a thread can lock the entire service, preventing any other threads in the system from locking the service or any names in the service.


Method Summary
abstract  void becomeLockGrantor()
          Specifies this member to become the grantor for this lock service.
static void becomeLockGrantor(String serviceName)
          Specifies that this member should become the grantor for the named locking service.
static DistributedLockService create(String serviceName, DistributedSystem ds)
          Create a DistributedLockService with the given serviceName for the given DistributedSystem.
static void destroy(String serviceName)
          Destroy a previously created DistributedLockService with the given serviceName.
abstract  void freeResources(Object name)
          Free internal resources associated with the given name.
static DistributedLockService getServiceNamed(String serviceName)
          Look up and return the DistributedLockService with the given name, if it has been created in this VM.
abstract  boolean isHeldByCurrentThread(Object name)
          Determine whether the current thread owns the lock on the given object.
abstract  boolean isLockGrantor()
          Returns true if this member is currently the lock authority responsible for granting locks for this service.
static boolean isLockGrantor(String serviceName)
          Returns true if this member is the grantor for the named service.
abstract  boolean isLockingSuspendedByCurrentThread()
          Determine whether the current thread has suspended locking in this DistributedLockService.
abstract  boolean lock(Object name, long waitTimeMillis, long leaseTimeMillis)
          Attempts to acquire a lock named name.
abstract  boolean lockInterruptibly(Object name, long waitTimeMillis, long leaseTimeMillis)
          Deprecated. as of GemFire 5.1, use lock(Object, long, long) with waitTimeMillis instead
abstract  void resumeLocking()
          Allow locking to resume in this DistributedLockService instance.
abstract  boolean suspendLocking(long waitTimeMillis)
          Suspend granting of locks in this service.
abstract  boolean suspendLockingInterruptibly(long waitTimeMillis)
          Deprecated. as of GemFire 5.1, use suspendLocking(long) with waitTimeMillis instead
abstract  void unlock(Object name)
          Release the lock previously granted for the given name.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Method Detail

create

public static DistributedLockService create(String serviceName,
                                            DistributedSystem ds)
                                     throws IllegalArgumentException
Create a DistributedLockService with the given serviceName for the given DistributedSystem. This DistributedLockService will continue to manage locks until destroy(java.lang.String) is called, or ds is disconnected, at which point any locks that were held by this instance are released.

Parameters:
serviceName - the name of the DistributedLockService to create.
ds - the DistributedSystem for the new service instance to use for distributed lock messaging.
Throws:
IllegalArgumentException - if serviceName is an illegal name or this process has already created a DistributedLockService with the given serviceName.
IllegalStateException - if this process is in the middle of disconnecting from the DistributedSystem

getServiceNamed

public static DistributedLockService getServiceNamed(String serviceName)
Look up and return the DistributedLockService with the given name, if it has been created in this VM. If it has not been created, return null.

Parameters:
serviceName - the name of the DistributedLockService to look up
Returns:
the DistributedLockService with the given name, or null if it hasn't been created in this VM.

destroy

public static void destroy(String serviceName)
                    throws IllegalArgumentException
Destroy a previously created DistributedLockService with the given serviceName. Any locks currently held in this DistributedLockService by this process are released. Attempts to access a destroyed lock service will result in a LockServiceDestroyedException being thrown.

Parameters:
serviceName - the name of the instance to destroy, previously supplied in the create(String, DistributedSystem) invocation.
Throws:
IllegalArgumentException - if this process hasn't created a DistributedLockService with the given serviceName and dm.

lock

public abstract boolean lock(Object name,
                             long waitTimeMillis,
                             long leaseTimeMillis)

Attempts to acquire a lock named name. Returns true as soon as the lock is acquired. If the lock is currently held by another thread in this or any other process in the distributed system, or another thread in the system has locked the entire service, this method keeps trying to acquire the lock for up to waitTimeMillis before giving up and returning false. If the lock is acquired, it is held until unlock(Object name) is invoked, or until leaseTimeMillis milliseconds have passed since the lock was granted - whichever comes first.

Locks are reentrant. If a thread invokes this method n times on the same instance, specifying the same name, without an intervening release or lease expiration expiration on the lock, the thread must invoke unlock(name) the same number of times before the lock is released (unless the lease expires). When this method is invoked for a lock that is already acquired, the lease time will be set to the maximum of the remaining least time from the previous invocation, or leaseTimeMillis

Parameters:
name - the name of the lock to acquire in this service. This object must conform to the general contract of equals(Object) and hashCode() as described in Object.hashCode().
waitTimeMillis - the number of milliseconds to try to acquire the lock before giving up and returning false. A value of -1 causes this method to block until the lock is acquired. A value of 0 causes this method to return false without waiting for the lock if the lock is held by another member or thread.
leaseTimeMillis - the number of milliseconds to hold the lock after granting it, before automatically releasing it if it hasn't already been released by invoking unlock(Object). If leaseTimeMillis is -1, hold the lock until explicitly unlocked.
Returns:
true if the lock was acquired, false if the timeout waitTimeMillis passed without acquiring the lock.
Throws:
LockServiceDestroyedException - if this lock service has been destroyed

lockInterruptibly

public abstract boolean lockInterruptibly(Object name,
                                          long waitTimeMillis,
                                          long leaseTimeMillis)
                                   throws InterruptedException
Deprecated. as of GemFire 5.1, use lock(Object, long, long) with waitTimeMillis instead

Attempts to acquire a lock named name. Returns true as soon as the lock is acquired. If the lock is currently held by another thread in this or any other process in the distributed system, or another thread in the system has locked the entire service, this method keeps trying to acquire the lock for up to waitTimeMillis before giving up and returning false. If the lock is acquired, it is held until unlock(Object name) is invoked, or until leaseTimeMillis milliseconds have passed since the lock was granted - whichever comes first.

Locks are reentrant. If a thread invokes this method n times on the same instance, specifying the same name, without an intervening release or lease expiration expiration on the lock, the thread must invoke unlock(name) the same number of times before the lock is released (unless the lease expires). When this method is invoked for a lock that is already acquired, the lease time will be set to the maximum of the remaining least time from the previous invocation, or leaseTimeMillis

Parameters:
name - the name of the lock to acquire in this service. This object must conform to the general contract of equals(Object) and hashCode() as described in Object.hashCode().
waitTimeMillis - the number of milliseconds to try to acquire the lock before giving up and returning false. A value of -1 causes this method to block until the lock is acquired.
leaseTimeMillis - the number of milliseconds to hold the lock after granting it, before automatically releasing it if it hasn't already been released by invoking unlock(Object). If leaseTimeMillis is -1, hold the lock until explicitly unlocked.
Returns:
true if the lock was acquired, false if the timeout waitTimeMillis passed without acquiring the lock.
Throws:
InterruptedException - if the thread is interrupted before or during this method.
LockServiceDestroyedException - if this lock service has been destroyed

unlock

public abstract void unlock(Object name)
                     throws LeaseExpiredException
Release the lock previously granted for the given name.

Parameters:
name - the object to unlock in this service.
Throws:
LockNotHeldException - if the current thread is not the owner of this lock
LeaseExpiredException - if the current thread was the owner of this lock, but it's lease has expired.
LockServiceDestroyedException - if the service has been destroyed

isHeldByCurrentThread

public abstract boolean isHeldByCurrentThread(Object name)
Determine whether the current thread owns the lock on the given object.

Returns:
true if the current thread owns the lock for name.
Throws:
LockServiceDestroyedException - if this service has been destroyed

suspendLockingInterruptibly

public abstract boolean suspendLockingInterruptibly(long waitTimeMillis)
                                             throws InterruptedException
Deprecated. as of GemFire 5.1, use suspendLocking(long) with waitTimeMillis instead

Suspend granting of locks in this service. When locking has been suspended, no other thread in the distributed system will be granted a lock for any new or existing name in that service until locking is resumed by the thread that suspended it. Only one thread at a time in a distributed system is permitted suspend locking on a given DistributedLockService instance. This method blocks until lock suspension can be granted to the current thread, and all outstanding locks on names in this service held by other threads in the distributed system have been released, or until waitTimeMillis milliseconds have passed without successfully granting suspension.

Parameters:
waitTimeMillis - the number of milliseconds to try to acquire suspension before giving up and returning false. A value of -1 causes this method to block until suspension is granted.
Returns:
true if suspension was granted, false if the timeout waitTimeMillis passed before it could be granted.
Throws:
IllegalStateException - if the current thread already has suspended locking on this instance.
InterruptedException - if the current thread is interrupted.
LockServiceDestroyedException - if the service has been destroyed

suspendLocking

public abstract boolean suspendLocking(long waitTimeMillis)
Suspend granting of locks in this service. When locking has been suspended, no other thread in the distributed system will be granted a lock for any new or existing name in that service until locking is resumed by the thread that suspended it. Only one thread at a time in a distributed system is permitted suspend locking on a given DistributedLockService instance. This method blocks until lock suspension can be granted to the current thread, and all outstanding locks on names in this service held by other threads in the distributed system have been released, or until waitTimeMillis milliseconds have passed without successfully granting suspension.

Parameters:
waitTimeMillis - the number of milliseconds to try to acquire suspension before giving up and returning false. A value of -1 causes this method to block until suspension is granted. A value of 0 causes this method to return false without waiting for the lock if the lock is held by another member or thread.
Returns:
true if suspension was granted, false if the timeout waitTimeMillis passed before it could be granted.
Throws:
IllegalStateException - if the current thread already has suspended locking on this instance
LockServiceDestroyedException - if the service has been destroyed

resumeLocking

public abstract void resumeLocking()
Allow locking to resume in this DistributedLockService instance.

Throws:
IllegalStateException - if the current thread didn't previously suspend locking
LockServiceDestroyedException - if the service has been destroyed

isLockingSuspendedByCurrentThread

public abstract boolean isLockingSuspendedByCurrentThread()
Determine whether the current thread has suspended locking in this DistributedLockService.

Returns:
true if locking is suspended by the current thread.
Throws:
LockServiceDestroyedException - if this service has been destroyed

freeResources

public abstract void freeResources(Object name)
Free internal resources associated with the given name. This may reduce this VM's memory use, but may also prohibit performance optimizations if name is subsequently locked in this VM.

Throws:
LockServiceDestroyedException - if this service has been destroyed

becomeLockGrantor

public abstract void becomeLockGrantor()
Specifies this member to become the grantor for this lock service. The grantor will be the lock authority which is responsible for handling all lock requests for this service. Other members will request locks from this member. Locking for this member is optimized as it will not require messaging to acquire a given lock.

Calls to this method will block until grantor authority has been transferred to this member.

If another member calls becomeLockGrantor after this member, that member will transfer grantor authority from this member to itself.

This operation should not be invoked repeatedly in an application. It is possible to create a lock service and have two or more members endlessly calling becomeLockGrantor to transfer grantorship back and forth.

Throws:
LockServiceDestroyedException - if this service has been destroyed

becomeLockGrantor

public static void becomeLockGrantor(String serviceName)
                              throws IllegalArgumentException
Specifies that this member should become the grantor for the named locking service.

Parameters:
serviceName - the name of the locking service
Throws:
IllegalArgumentException - if serviceName does not refer to any registered locking service in this process
See Also:
becomeLockGrantor()

isLockGrantor

public abstract boolean isLockGrantor()
Returns true if this member is currently the lock authority responsible for granting locks for this service. This can be explicitly requested by calling becomeLockGrantor(). If no member has explicitly requested grantor authority, then one member participating in the service will be implicitly selected. In either case, this method returns true if the calling member is the grantor.

Returns:
true if this member is the grantor for this service
Throws:
LockServiceDestroyedException - if lock service has been destroyed

isLockGrantor

public static boolean isLockGrantor(String serviceName)
                             throws IllegalArgumentException
Returns true if this member is the grantor for the named service.

Parameters:
serviceName - the name of the locking service
Returns:
true if this member is the grantor for this service
Throws:
IllegalArgumentException - if serviceName does not refer to any registered locking service in this process
See Also:
isLockGrantor()

GemFire 5.5

Copyright © 2002-2008 GemStone Systems, Inc. All Rights Reserved.