org.exolab.castor.persist
Class LockEngine

java.lang.Object
  org.exolab.castor.persist.LockEngine

public final class LockEngine
extends Object

LockEngine is a gateway for all the ClassMolders of a persistence storage. It maintains dirty checking cache state and lock, and provides a thread safe environment for ClassMolder. LockEngine guarantees that no two conflicting operations will be let running concurrently for the same object.

For example, it ensures that exactly one transaction may read (load) exclusively on one object; transaction can not deleted an object while the other is reading it, etc...

User should not create more than one instance of LockEngine for each persistent storage. So that object can be properly locked and ObjectModifiedException can be avoided.

However, if more than one instance of LockEngine or some other external application run concurrently, if the Persistence supports dirty checking, like a fully complaint JDBC Relational Database, proper ObjectModifiedException will be thrown to ensure data consistency.

IMPLEMENTATION NOTES:

An object may be persistent in multiple caches at any given time. There is no way to load an object from multiple caches, but an object can be loaded in one engine and then made persistent in another. The engines are totally independent and no conflicts should occur.

Version:

$Revision: 9042 $ $Date: 2011-08-16 18:41:15 +0200 (Di, 16 Aug 2011) $

Author:

Assaf Arkin, Thomas Yip, Bruce Snyder

Constructor Summary

LockEngine(DatabaseContext databaseContext, ClassDescriptorResolver cdResolver, PersistenceFactory persistenceFactory)
Construct a new cache engine with the specified mapping table, persistence engine and the log intercepter.

Method Summary

void	closeCaches() Close all caches (to allow for resource clean-up).
OID	create(TransactionContext tx, OID oid, Object object) Creates a new object in the persistence storage.
void	delete(TransactionContext tx, OID oid) Called at transaction commit time to delete the object.
void	dumpCache() Dump cached objects of all types to output.
void	dumpCache(Class<?> cls) Dump cached objects of specific type to output.
void	expireCache() Expires all objects of all types from cache.
void	expireCache(Class<?> cls) Forces the cache to be expired for the object represented by ClassMolder and identity.
boolean	expireCache(TransactionContext tx, OID oid, int timeout) Expire object from the cache.
void	forgetObject(TransactionContext tx, OID oid) Called at transaction commit or rollback to forget an object and release its locks.
ClassMolderRegistry	getClassMolderRegistry()
DatabaseContext	getDatabaseContext()
Persistence	getPersistence(Class<?> cls) Get the persistence of the specified class.
PersistenceFactory	getPersistenceFactory()
HashMap<Xid,TransactionContext>	getXATransactions() Returns an association between Xid and transactions contexts.
boolean	isCached(Class<?> cls, OID oid) Provides information about whether an object of Class cls with identity iod is currently cached.
boolean	isLocked(Class<?> cls, OID oid) Indicates whether an object with the specified OID is currently locked.
void	load(AbstractTransactionContext tx, OID oid, ProposedEntity proposedObject, AccessMode suggestedAccessMode, int timeout, QueryResults results, ClassMolder paramMolder, Identity identity) Loads an object of the specified type and identity from persistent storage.
void	markCreate(TransactionContext tx, OID oid, Object object) Mark an object and its related or dependent object to be created.
void	markDelete(TransactionContext tx, OID oid, Object object, int timeout) Make the object is deleted.
OID	preStore(TransactionContext tx, OID oid, Object object, int timeout) Called at transaction commit to store an object that has been loaded during the transaction.
void	releaseLock(TransactionContext tx, OID oid) Called at transaction commit or rollback to release all locks held on the object.
void	revertObject(TransactionContext tx, OID oid, Object object) Reverts an object to the cached copy given the object's OID.
void	softLock(TransactionContext tx, OID oid, int timeout) Acquire a write lock on the object in memory.
void	store(TransactionContext tx, OID oid, Object object) Store the object in TransactionContext.
boolean	update(AbstractTransactionContext tx, OID oid, Object object, AccessMode suggestedAccessMode, int timeout) Updates an existing object to this engine.
void	updateCache(TransactionContext tx, OID oid, Object object) Update the cached object with changes done to its copy.
void	writeLock(TransactionContext tx, OID oid, int timeout) Acquire a write lock on the object.

Methods inherited from class java.lang.Object

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

Constructor Detail

LockEngine

public LockEngine(DatabaseContext databaseContext,
                  ClassDescriptorResolver cdResolver,
                  PersistenceFactory persistenceFactory)
           throws MappingException

Construct a new cache engine with the specified mapping table, persistence engine and the log intercepter.

Parameters:

databaseContext - the databaseContext

cdResolver - the cdResolver

persistenceFactory - Factory for creating persistence engines for each object described in the map.

Throws:

MappingException - Indicate that one of the mappings is invalid

Method Detail

getDatabaseContext

public DatabaseContext getDatabaseContext()

Returns:

The ConnectionFactory

getClassMolderRegistry

public ClassMolderRegistry getClassMolderRegistry()

Returns:

the ClassMolderRegistry for the LockEngine

getPersistence

public Persistence getPersistence(Class<?> cls)

Get the persistence of the specified class.

Parameters:

cls - the specified class

Returns:

the persistence which the class uses.

load

public void load(AbstractTransactionContext tx,
                 OID oid,
                 ProposedEntity proposedObject,
                 AccessMode suggestedAccessMode,
                 int timeout,
                 QueryResults results,
                 ClassMolder paramMolder,
                 Identity identity)
          throws PersistenceException

Loads an object of the specified type and identity from persistent storage. In exclusive mode the object is always loaded and a write lock is obtained on the object, preventing concurrent updates. In non-exclusive mode the object is either loaded or obtained from the cache with a read lock. The object's OID is always returned.

Parameters:

tx - The transaction context

oid - The identity of the object to load

proposedObject - The type of the object to load

suggestedAccessMode - The desired access mode

timeout - The timeout waiting to acquire a lock on the object (specified in seconds)

results - the QueryResults

paramMolder - the ClassMolder

identity - the Identity

Throws:

PersistenceException - An error reported by the persistence engine

markCreate

public void markCreate(TransactionContext tx,
                       OID oid,
                       Object object)
                throws PersistenceException

Mark an object and its related or dependent object to be created.

Parameters:

tx - The transaction context.

oid - The identity of the object, or null.

object - The newly created object.

Throws:

PersistenceException - An error reported by the persistence engine. Timeout or deadlock occurred attempting to acquire lock on object.

create

public OID create(TransactionContext tx,
                  OID oid,
                  Object object)
           throws PersistenceException

Creates a new object in the persistence storage. The object must not be persistent and must have a unique identity within this engine. If the identity is specified the object is created in persistent storage immediately with the identity. If the identity is not specified, the object is created only when the transaction commits. The object's OID is returned. The OID is guaranteed to be unique for this engine even if no identity was specified.

Parameters:

tx - The transaction context

oid - The identity of the object, or null

object - The newly created object

Returns:

The object's OID

Throws:

PersistenceException - An error reported by the persistence engine

delete

public void delete(TransactionContext tx,
                   OID oid)
            throws PersistenceException

Called at transaction commit time to delete the object. Object deletion occurs in three distinct steps:

• A write lock is obtained on the object to assure it can be deleted and the object is marked for deletion in the transaction context
• As part of transaction preparation the object is deleted from persistent storage using this method
• The object is removed from the cache when the transaction completes with a call to forgetObject(org.castor.persist.TransactionContext, org.exolab.castor.persist.OID)

Parameters:

tx - The transaction context

oid - The object's identity

Throws:

PersistenceException - An error reported by the persistence engine

markDelete

public void markDelete(TransactionContext tx,
                       OID oid,
                       Object object,
                       int timeout)
                throws PersistenceException

Make the object is deleted.

Parameters:

tx - The transaction context

oid - The object's identity

object - The object

timeout - The timeout

Throws:

PersistenceException - If the lock is not granted

update

public boolean update(AbstractTransactionContext tx,
                      OID oid,
                      Object object,
                      AccessMode suggestedAccessMode,
                      int timeout)
               throws PersistenceException

Updates an existing object to this engine. The object must not be persistent and must not have the identity of a persistent object. The object's OID is returned. The OID is guaranteed to be unique for this engine even if no identity was specified. If the object implements TimeStampable interface, verify the object's timestamp.

Parameters:

tx - The transaction context

oid - The object's identity

object - The object

suggestedAccessMode - The desired access mode

timeout - The timeout waiting to acquire a lock on the object (specified in seconds)

Returns:

true if the update succeed

Throws:

PersistenceException - An error reported by the persistence engine, or lock, or concurrent modification

preStore

public OID preStore(TransactionContext tx,
                    OID oid,
                    Object object,
                    int timeout)
             throws PersistenceException

Called at transaction commit to store an object that has been loaded during the transaction. If the object has been created in this transaction but without an identity, the object will be created in persistent storage. Otherwise the object will be stored and dirty checking might occur in order to determine whether the object is valid. The object's OID might change during this process, and the new OID will be returned. If the object was not stored (not modified), null is returned.

Parameters:

tx - The transaction context

oid - The object's identity

object - The object to store

timeout - The timeout waiting to acquire a lock on the object (specified in seconds)

Returns:

The object's OID if stored, null if ignored

Throws:

PersistenceException - An error reported by the persistence engine, lock, or concurrent modification

store

public void store(TransactionContext tx,
                  OID oid,
                  Object object)
           throws PersistenceException

Store the object in TransactionContext.

Parameters:

tx - The transaction context

oid - The object's OID

object - the object

Throws:

PersistenceException - n error reported by the persistence engine, or lock

writeLock

public void writeLock(TransactionContext tx,
                      OID oid,
                      int timeout)
               throws PersistenceException

Acquire a write lock on the object. A write lock assures that the object exists and can be stored/deleted when the transaction commits. It prevents any concurrent updates to the object from this point on. However, it does not guarantee that the object has not been modified in the course of the transaction. For that the object must be loaded with exclusive access.

Parameters:

tx - The transaction context

oid - The object's OID

timeout - The timeout waiting to acquire a lock on the object (specified in seconds)

Throws:

PersistenceException - An error reported by the persistence engine, or lock

softLock

public void softLock(TransactionContext tx,
                     OID oid,
                     int timeout)
              throws LockNotGrantedException

Acquire a write lock on the object in memory. A soft lock prevents other threads from changing the object, but does not acquire a lock on the database.

Parameters:

tx - The transaction context

oid - The object's OID

timeout - The timeout waiting to acquire a lock on the object (specified in seconds)

Throws:

LockNotGrantedException - Timeout or deadlock occurred attempting to acquire lock on object persistent storage

revertObject

public void revertObject(TransactionContext tx,
                         OID oid,
                         Object object)
                  throws PersistenceException

Reverts an object to the cached copy given the object's OID. The cached object is copied into the supplied object without affecting the locks, loading relations or emitting errors. This method is used during the rollback phase.

Parameters:

tx - The transaction context

oid - The object's oid

object - The object into which to copy

Throws:

PersistenceException - An error reported by the persistence engine obtaining a dependent object

updateCache

public void updateCache(TransactionContext tx,
                        OID oid,
                        Object object)

Update the cached object with changes done to its copy. The supplied object is copied into the cached object using a write lock. This method is generally called after a successful return from store(org.castor.persist.TransactionContext, org.exolab.castor.persist.OID, java.lang.Object) and is assumed to have obtained a write lock.

Parameters:

tx - The transaction context

oid - The object's oid

object - The object to copy from

releaseLock

public void releaseLock(TransactionContext tx,
                        OID oid)

Called at transaction commit or rollback to release all locks held on the object. Must be called for all objects that were queried but not created within the transaction.

Parameters:

tx - The transaction context

oid - The object OID

forgetObject

public void forgetObject(TransactionContext tx,
                         OID oid)

Called at transaction commit or rollback to forget an object and release its locks. Must be called for all objects that were created when the transaction aborts, and for all objects that were deleted when the transaction completes. The transaction is known to have a write lock on the object.

Parameters:

tx - The transaction context

oid - The object OID

expireCache

public boolean expireCache(TransactionContext tx,
                           OID oid,
                           int timeout)
                    throws PersistenceException

Expire object from the cache. If the object to be expired is currently cached, then a write lock is first acquired for this object. In addition, a write lock is acquired on all objects related to, or contained within, this object. The version of the objects represented by their locks is then marked as "expired". Upon the release of each write lock (@see TransactionContext#expireCache), the cached version of the objects will not be placed back in the cache (@see TypeInfo#release). A subsequent read/query transaction will therefore load the values of the object from persistent storage.

Parameters:

tx - The transaction context

oid - The object OID

timeout - The max time to wait while acquiring a lock on the object (specified in seconds)

Returns:

True if the object was expired successfully from the cache.

Throws:

PersistenceException - An error reported by the persistence engine, or lock

expireCache

public void expireCache(Class<?> cls)

Forces the cache to be expired for the object represented by ClassMolder and identity. If identity is null then expire all objects of the type represented by ClassMolder.

Parameters:

cls - Class type instance.

expireCache

public void expireCache()

Expires all objects of all types from cache.

dumpCache

public void dumpCache()

Dump cached objects of all types to output.

closeCaches

public void closeCaches()

Close all caches (to allow for resource clean-up).

dumpCache

public void dumpCache(Class<?> cls)

Dump cached objects of specific type to output.

Parameters:

cls - A class type.

getXATransactions

public HashMap<Xid,TransactionContext> getXATransactions()

Returns an association between Xid and transactions contexts. The association is shared between all transactions open against this cache engine through the XAResource interface.

Returns:

Association between XId and transaction contexts.

isCached

public boolean isCached(Class<?> cls,
                        OID oid)

Provides information about whether an object of Class cls with identity iod is currently cached.

Parameters:

cls - Class type.

oid - Object identity

Returns:

True if the specified object is in the cache.

isLocked

public boolean isLocked(Class<?> cls,
                        OID oid)

Indicates whether an object with the specified OID is currently locked.

Parameters:

cls - Class type.

oid - Object identity

Returns:

True if the object is locked.

getPersistenceFactory

public PersistenceFactory getPersistenceFactory()

Returns:

PersistenceFactory instance currently set.