org.exolab.castor.persist

Class TransactionContext

public abstract class TransactionContext extends Object

A transaction context is required in order to perform operations against the database. The transaction context is mapped to an API transaction or an XA transaction. The only way to begin a new transaction is through the creation of a new transaction context. A transaction context is created from an implementation class directly or through XAResourceImpl.

Version: $Revision: 1.2 $ $Date: 2003/03/03 17:18:29 $

Author: Assaf Arkin

Nested Class Summary
static classTransactionContext.ObjectEntry
A transaction records all objects accessed during the lifetime of the transaction in this record (queries and created).
Field Summary
static intOBJECT_STATE_HOLLOW
static intOBJECT_STATE_PERSISTENT
static intOBJECT_STATE_PERSISTENT_DELETED
static intOBJECT_STATE_PERSISTENT_NEW
static intOBJECT_STATE_PERSISTENT_NEW_DELETED
static intOBJECT_STATE_READ_ONLY
static intOBJECT_STATE_TRANSIENT
IMPLEMENTATION NOTES: An object is considered persistent only if it was queried or created within the context of this transaction.
Constructor Summary
TransactionContext(Database db)
Create a new transaction context.
TransactionContext(Database db, Xid xid)
Create a new transaction context.
Method Summary
TransactionContext.ObjectEntryaddObjectEntry(OID oid, Object object)
Adds a new entry recording the use of the object in this transaction.
voidaddTxSynchronizable(TxSynchronizable synchronizable)
Register a listener which wants to synchronize its state to the state of the transaction.
voidclose()
Closes all Connections.
protected abstract voidcloseConnections()
The derived class must implement this method and close all the connections used in this transaction.
voidcommit()
Commits all changes and closes the transaction releasing all locks on all objects.
protected abstract voidcommitConnections()
The derived class must implement this method and commit all the connections used in this transaction.
voidcreate(LockEngine engine, ClassMolder molder, Object object, OID depended)
Creates a new object in persistent storage.
voiddelete(Object object)
Deletes the object from persistent storage.
Objectfetch(LockEngine engine, ClassMolder molder, Object identity, AccessMode suggestedAccessMode)
ClassLoadergetClassLoader()
Get the current application ClassLoader.
abstract ObjectgetConnection(LockEngine engine)
The derived class must implement this method and return an open connection for the specified engine.
DatabasegetDatabase()
ObjectgetIdentity(Object object)
Returns the object's identity.
intgetLockTimeout()
Returns the timeout waiting to acquire a lock.
TransactionContext.ObjectEntrygetObjectEntry(LockEngine engine, OID oid)
Retrieves the object entry for the specified object.
TransactionContext.ObjectEntrygetObjectEntry(Object object)
Returns the entry for the object from the object.
intgetObjectState(Object object)
TransactionContext.ObjectEntrygetReadOnlyObjectEntry(OID oid)
PersistenceInfoGroupgetScope()
intgetStatus()
Returns the status of this transaction.
intgetTransactionTimeout()
Returns the timeout of this transaction.
ObjectLockgetWaitOnLock()
Returns the lock which this transaction attempts to acquire.
protected XidgetXid()
booleanisAutoStore()
Test if autoStore options is enabled or not.
booleanisDeleted(Object object)
True if and only if the specified object is loaded or created in this transaction and is deleted.
booleanisDeletedByOID(OID oid)
booleanisDepended(OID master, Object dependent)
booleanisOpen()
Returns true if the transaction is open.
booleanisPersistent(Object object)
Returns true if the object is persistent in this transaction.
booleanisReadOnly(Object object)
booleanisRecorded(Object object)
Returns true if the object is previously queried/loaded/update/create in this transaction
Objectload(LockEngine engine, ClassMolder molder, Object identity, Object objectToBeLoaded, AccessMode suggestedAccessMode)
Load an object for use within the transaction.
Objectload(LockEngine engine, ClassMolder molder, Object identity, Object objectToBeLoaded, AccessMode suggestedAccessMode, QueryResults results)
Load an object for use within the transaction.
voidmakeReadOnly(Object object)
Makes the object read-only: move it to the hashtable of readonly objects The object must be already in the transaction.
voidmarkCreate(LockEngine engine, ClassMolder molder, Object object, OID depended)
Walk a data object tree starting from the specified object, and mark all object to be created.
voidmarkDelete(LockEngine engine, Class type, Object identity)
Marks an object for deletion.
voidmarkModified(Object object, boolean updatePersist, boolean updateCache)
booleanmarkUpdate(LockEngine engine, ClassMolder molder, Object object, OID depended)
Update a new object in persistent storage and returns the object's OID.
booleanprepare()
Prepares the transaction prior to committing it.
QueryResultsquery(LockEngine engine, PersistenceQuery query, AccessMode accessMode, boolean scrollable)
Perform a query using the query mechanism and in the specified access mode.
QueryResultsquery(LockEngine engine, PersistenceQuery query, AccessMode accessMode)
TransactionContext.ObjectEntryrehash(Object object, OID oid)
voidrelease(Object object)
Releases the lock granted on the object.
TransactionContext.ObjectEntryremoveObjectEntry(Object object)
Removes the entry for an object and returns it.
voidremoveTxSynchronizable(TxSynchronizable synchronizable)
voidrollback()
protected abstract voidrollbackConnections()
The derived class must implement this method and rollback all the connections used in this transaction.
voidsetAutoStore(boolean autoStore)
Enable or disable autoStore.
voidsetCallback(CallbackInterceptor callback)
Overrides the default callback interceptor by a custom interceptor for this database source.
voidsetInstanceFactory(InstanceFactory factory)
Overrides the default instance factory by a custom one for this database source.
voidsetLockTimeout(int timeout)
Sets the timeout waiting to acquire a lock.
voidsetTransactionTimeout(int timeout)
Sets the timeout of this transaction.
voidsetWaitOnLock(ObjectLock lock)
Indicates which lock this transaction is waiting for.
voidsoftLock(Object object, int timeout)
Acquire a write lock on the object.
static shorttoDatabaseAccessMode(AccessMode mode)
Converts AccessMode constant to Database short constant
protected voidtxcommitted()
Inform all registered listeners that the transaction was committed.
protected voidtxrolledback()
Inform all registered listeners that the transaction was rolled back.
voidupdate(LockEngine engine, ClassMolder molder, Object object, OID depended)
Update a new object in persistent storage and returns the object's OID.
voidwriteLock(Object object, int timeout)
Acquire a write lock on the object.

Field Detail

OBJECT_STATE_HOLLOW

public static int OBJECT_STATE_HOLLOW

OBJECT_STATE_PERSISTENT

public static int OBJECT_STATE_PERSISTENT

OBJECT_STATE_PERSISTENT_DELETED

public static int OBJECT_STATE_PERSISTENT_DELETED

OBJECT_STATE_PERSISTENT_NEW

public static int OBJECT_STATE_PERSISTENT_NEW

OBJECT_STATE_PERSISTENT_NEW_DELETED

public static int OBJECT_STATE_PERSISTENT_NEW_DELETED

OBJECT_STATE_READ_ONLY

public static int OBJECT_STATE_READ_ONLY

OBJECT_STATE_TRANSIENT

public static int OBJECT_STATE_TRANSIENT
IMPLEMENTATION NOTES: An object is considered persistent only if it was queried or created within the context of this transaction. An object is not persistent if it was queried or created by another transactions. An object is not persistent if it was queried with read-only access. A read lock is implicitly obtained on any object that is queried, and a write lock on any object that is queried in exclusive mode, created or deleted in this transaction. The lock can be upgraded to a write lock. The validity of locks is dependent on the underlying persistence engine the transaction mode. Without persistence engine locks provide a strong locking mechanism, preventing objects from being deleted or modified in one transaction while another transaction is looking at them. With a persistent engine in exclusive mode, locks exhibit the same behavior. With a persistent engine in read/write mode or a persistent engine that does not support locking (e.g. LDAP) an object may be deleted or modified concurrently through a direct access mechanism.

Constructor Detail

TransactionContext

public TransactionContext(Database db)
Create a new transaction context. This method is used by the explicit transaction model.

TransactionContext

public TransactionContext(Database db, Xid xid)
Create a new transaction context. This method is used by the XA transaction model, see XAResourceImpl.

Method Detail

addObjectEntry

TransactionContext.ObjectEntry addObjectEntry(OID oid, Object object)
Adds a new entry recording the use of the object in this transaction. This is a copy of the object that is only visible (or deleted) in the context of this transaction. The object is not persisted if it has not been recorded in this transaction.

Parameters: object The object to record oid The object's OID engine The persistence engine used to create this object

addTxSynchronizable

public void addTxSynchronizable(TxSynchronizable synchronizable)
Register a listener which wants to synchronize its state to the state of the transaction.

close

public void close()
Closes all Connections. Must be called before the end of the transaction in EJB environment or after commit in standalone case.

Throws: TransactionAbortedException The transaction has been aborted due to inconsistency, duplicate object identity, error with the persistence engine or any other reason IllegalStateException This method has been called after the end of the transaction.

closeConnections

protected abstract void closeConnections()
The derived class must implement this method and close all the connections used in this transaction.

Throws: TransactionAbortedException The transaction could not close all the connections

commit

public void commit()
Commits all changes and closes the transaction releasing all locks on all objects. All objects are now transient. Must be called after a call to TransactionContext has returned successfully.

Throws: TransactionAbortedException The transaction has been aborted due to inconsistency, duplicate object identity, error with the persistence engine or any other reason IllegalStateException This method has been called without calling TransactionContext first

commitConnections

protected abstract void commitConnections()
The derived class must implement this method and commit all the connections used in this transaction. If the transaction could not commit fully or partially, this method will throw an TransactionAbortedException, causing a rollback to occur as the next step.

Throws: TransactionAbortedException The transaction could not commit fully or partially and should be rolled back

create

public void create(LockEngine engine, ClassMolder molder, Object object, OID depended)
Creates a new object in persistent storage. The object will be persisted only if the transaction commits. If an identity is provided then duplicate identity check happens in this method, if no identity is provided then duplicate identity check occurs when the transaction completes and the object is not visible in this transaction.

Parameters: engine The persistence engine molder The molder of the creating class object The object to persist depended The master object's OID if exist

Returns: The object's OID

Throws: DuplicateIdentityException An object with this identity already exists in persistent storage PersistenceException An error reported by the persistence engine ClassNotPersistenceCapableException The class is not persistent capable

delete

public void delete(Object object)
Deletes the object from persistent storage. The deletion will take effect only if the transaction is committed, but the object is no longer viewable for the current transaction and locks for access from other transactions will block until this transaction completes. A write lock is acquired in order to assure the object can be deleted.

Parameters: object The object to delete from persistent storage

Throws: ObjectNotPersistentException The object has not been queried or created in this transaction LockNotGrantedException Timeout or deadlock occured attempting to acquire lock on object PersistenceException An error reported by the persistence engine

fetch

public Object fetch(LockEngine engine, ClassMolder molder, Object identity, AccessMode suggestedAccessMode)

getClassLoader

public ClassLoader getClassLoader()
Get the current application ClassLoader.

Returns: the current ClassLoader's instance. null if none has been provided

getConnection

public abstract Object getConnection(LockEngine engine)
The derived class must implement this method and return an open connection for the specified engine. The connection should be created only one for a given engine in the same transaction.

Parameters: engine The persistence engine

Returns: An open connection

Throws: PersistenceException An error occured talking to the persistence engine

getDatabase

public Database getDatabase()

getIdentity

public Object getIdentity(Object object)
Returns the object's identity. If the identity was determined when the object was created, or if the object was retrieved, that identity is returned. If the identity has been modified, this will not be reflected until the transaction commits. Null is returned if the identity is null, the object does not have any identity, or the object is not persistent.

Parameters: object The object

Returns: The object's identity, or null

getLockTimeout

public int getLockTimeout()
Returns the timeout waiting to acquire a lock. The timeout is specified in seconds.

getObjectEntry

TransactionContext.ObjectEntry getObjectEntry(LockEngine engine, OID oid)
Retrieves the object entry for the specified object.

Parameters: engine The persistence engine used to create this object oid The object's OID

Returns: The object entry

getObjectEntry

TransactionContext.ObjectEntry getObjectEntry(Object object)
Returns the entry for the object from the object. If the entry does not exist, the object is not persistent in this transaction. An entry will be returned even if the object has been deleted in this transaction.

Parameters: object The object to locate

Returns: The object's entry or null if not persistent

getObjectState

public int getObjectState(Object object)

getReadOnlyObjectEntry

TransactionContext.ObjectEntry getReadOnlyObjectEntry(OID oid)

getScope

public PersistenceInfoGroup getScope()

getStatus

public int getStatus()
Returns the status of this transaction.

getTransactionTimeout

public int getTransactionTimeout()
Returns the timeout of this transaction. The timeout is specified in seconds.

getWaitOnLock

ObjectLock getWaitOnLock()
Returns the lock which this transaction attempts to acquire.

Returns: The lock which this transaction attempts to acquire

getXid

protected Xid getXid()

isAutoStore

public boolean isAutoStore()
Test if autoStore options is enabled or not.

isDeleted

public boolean isDeleted(Object object)
True if and only if the specified object is loaded or created in this transaction and is deleted.

isDeletedByOID

public boolean isDeletedByOID(OID oid)

isDepended

public boolean isDepended(OID master, Object dependent)

isOpen

public boolean isOpen()
Returns true if the transaction is open.

isPersistent

public boolean isPersistent(Object object)
Returns true if the object is persistent in this transaction.

Parameters: object The object

Returns: True if persistent in transaction

isReadOnly

public boolean isReadOnly(Object object)

isRecorded

public boolean isRecorded(Object object)
Returns true if the object is previously queried/loaded/update/create in this transaction

load

public Object load(LockEngine engine, ClassMolder molder, Object identity, Object objectToBeLoaded, AccessMode suggestedAccessMode)
Load an object for use within the transaction. Multiple access to the same object within the transaction will return the same object instance (except for read-only access).

This method is similar to TransactionContext except that it will load the object only once within a transaction and always return the same instance.

If the object is loaded for read-only then no lock is acquired and updates to the object are not reflected at commit time. If the object is loaded for read-write then a read lock is acquired (unless timeout or deadlock detected) and the object is stored at commit time. The object is then considered persistent and may be deleted or upgraded to write lock. If the object is loaded for exclusive access then a write lock is acquired and the object is synchronized with the persistent copy.

Attempting to load the object twice in the same transaction, once with exclusive lock and once with read-write lock will result in an exception.

Parameters: engine The persistence engine molder The class persistence molder object The object to fetch (single instance per transaction) identity The object's identity accessMode The access mode (see AccessMode) the values in persistent storage

Returns: object being loaded

Throws: LockNotGrantedException Timeout or deadlock occured attempting to acquire lock on object ObjectNotFoundException The object was not found in persistent storage PersistenceException An error reported by the persistence engine

load

public Object load(LockEngine engine, ClassMolder molder, Object identity, Object objectToBeLoaded, AccessMode suggestedAccessMode, QueryResults results)
Load an object for use within the transaction. Multiple access to the same object within the transaction will return the same object instance (except for read-only access).

This method work the same as load, except a QueryResults can be specified.

Parameters: engine The persistence engine molder The class persistence molder object The object to fetch (single instance per transaction) identity The object's identity accessMode The access mode (see AccessMode) the values in persistent storage results The QueryResult that the data to be loaded from.

Returns: object being loaded

Throws: LockNotGrantedException Timeout or deadlock occured attempting to acquire lock on object ObjectNotFoundException The object was not found in persistent storage PersistenceException An error reported by the persistence engine

makeReadOnly

void makeReadOnly(Object object)
Makes the object read-only: move it to the hashtable of readonly objects The object must be already in the transaction. Readonly objects should be unique in bounds of the transaction, otherwise they may be loaded twice (e.g.: one dependent object contains reference to another).

markCreate

public void markCreate(LockEngine engine, ClassMolder molder, Object object, OID depended)
Walk a data object tree starting from the specified object, and mark all object to be created.

Parameters: engine The persistence engine object The object to persist

Returns: The object's OID

Throws: DuplicateIdentityException An object with this identity already exists in persistent storage PersistenceException An error reported by the persistence engine ClassNotPersistenceCapableException The class is not persistent capable

markDelete

void markDelete(LockEngine engine, Class type, Object identity)
Marks an object for deletion. Used during the preparation stage to delete an attached relation by marking the object for deletion (if not already deleted) and preparing it a second time.

markModified

public void markModified(Object object, boolean updatePersist, boolean updateCache)

markUpdate

public boolean markUpdate(LockEngine engine, ClassMolder molder, Object object, OID depended)
Update a new object in persistent storage and returns the object's OID. The object will be persisted only if the transaction commits. If an identity is provided then duplicate identity check happens in this method, if no identity is provided then duplicate identity check occurs when the transaction completes and the object is not visible in this transaction.

Update will also mark object to be created if the TIMESTAMP equals to NO_TIMESTAMP.

Parameters: engine The persistence engine molder The object's molder object The object to persist depended The master objects of the specified object to be created if exisit

Returns: true if the object is marked to be created

Throws: DuplicateIdentityException An object with this identity already exists in persistent storage PersistenceException An error reported by the persistence engine ClassNotPersistenceCapableException The class is not persistent capable ObjectModifiedException Dirty checking mechanism may immediately report that the object was modified in the database during the long transaction.

prepare

public boolean prepare()
Prepares the transaction prior to committing it. Indicates whether the transaction is read-only (i.e. no modified objects), can commit, or an error has occured and the transaction must be rolled back. This method performs actual storage into the persistence storage. Multiple calls to this method can be done, and do not release locks, allowing checkpoint to occur.

Returns: True if the transaction can commit, false if the transaction is read only

Throws: IllegalStateException Method called if transaction is not in the proper state to perform this operation TransactionAbortedException The transaction has been aborted due to inconsistency, duplicate object identity, error with the persistence engine or any other reason

query

public QueryResults query(LockEngine engine, PersistenceQuery query, AccessMode accessMode, boolean scrollable)
Perform a query using the query mechanism and in the specified access mode. The query is performed in this transaction, and the returned query results can only be used while this transaction is open. It is assumed that the query mechanism is compatible with the persistence engine.

Parameters: engine The persistence engine query A query against the persistence engine accessMode The access mode

Returns: A query result iterator

Throws: QueryException An invalid query PersistenceException An error reported by the persistence engine

query

public QueryResults query(LockEngine engine, PersistenceQuery query, AccessMode accessMode)

rehash

TransactionContext.ObjectEntry rehash(Object object, OID oid)

release

public void release(Object object)
Releases the lock granted on the object. The object is removed from this transaction and will not participate in transaction commit/abort. Any changes done to the object are lost.

Parameters: object The object to release the lock

Throws: ObjectNotPersistentException The object was not queried or created in this transaction PersistenceException An error occured talking to the persistence engine

removeObjectEntry

TransactionContext.ObjectEntry removeObjectEntry(Object object)
Removes the entry for an object and returns it. The object is no longer part of the transaction.

Parameters: object The object to remove

Returns: The removed entry

removeTxSynchronizable

public void removeTxSynchronizable(TxSynchronizable synchronizable)

See Also: TransactionContext

rollback

public void rollback()

rollbackConnections

protected abstract void rollbackConnections()
The derived class must implement this method and rollback all the connections used in this transaction. The connections may be closed, as they will not be reused in this transaction. This operation is guaranteed to succeed.

setAutoStore

public void setAutoStore(boolean autoStore)
Enable or disable autoStore. If enabled, all new objects, which is reachable from other object that is quried, loaded, created in the transaction, will be created when the transaction is committed.

setCallback

public void setCallback(CallbackInterceptor callback)
Overrides the default callback interceptor by a custom interceptor for this database source.

The interceptor is a callback that notifies data objects on persistent state events.

If callback interceptor is not overrided, events will be sent to data object that implements the org.exolab.castor.jdo.Persistent interface.

Parameters: callback The callback interceptor, null if disabled

setInstanceFactory

public void setInstanceFactory(InstanceFactory factory)
Overrides the default instance factory by a custom one for this database source.

The factory is used to obatain a new instance of data object when it is needed during loading.

Parameters: instanceFactory The instanceFactory to be used, null if disable

setLockTimeout

public void setLockTimeout(int timeout)
Sets the timeout waiting to acquire a lock. The timeout is specified in seconds.

setTransactionTimeout

public void setTransactionTimeout(int timeout)
Sets the timeout of this transaction. The timeout is specified in seconds.

setWaitOnLock

void setWaitOnLock(ObjectLock lock)
Indicates which lock this transaction is waiting for. When a transaction attempts to acquire a lock it must indicate which lock it attempts to acquire in order to perform dead-lock detection. This method is called by ObjectLock before entering the temporary lock-acquire state.

Parameters: lock The lock which this transaction attempts to acquire

softLock

public void softLock(Object object, int timeout)
Acquire a write lock on the object. Read locks are implicitly available when the object is queried. A write lock is only granted for objects that are created or deleted or for objects loaded in exclusive mode - this method can obtain such a lock explicitly. If the object already has a write lock in this transaction or a read lock in this transaction but no read lock in any other transaction, a write lock is obtained. If this object has a read lock in any other transaction this method will block until the other transaction will release its lock. If the specified timeout has elapsed or a deadlock has been detected, an exception will be thrown but the current lock will be retained.

Parameters: object The object to lock timeout Timeout waiting to acquire lock, specified in seconds, zero for no waiting, negative to use the default timeout for this transaction

Throws: ObjectNotPersistentException The object has not been queried or created in this transaction LockNotGrantedException Timeout or deadlock occured attempting to acquire lock on object

toDatabaseAccessMode

static short toDatabaseAccessMode(AccessMode mode)
Converts AccessMode constant to Database short constant

txcommitted

protected void txcommitted()
Inform all registered listeners that the transaction was committed.

txrolledback

protected void txrolledback()
Inform all registered listeners that the transaction was rolled back.

update

public void update(LockEngine engine, ClassMolder molder, Object object, OID depended)
Update a new object in persistent storage and returns the object's OID. The object will be persisted only if the transaction commits. If an identity is provided then duplicate identity check happens in this method, if no identity is provided then duplicate identity check occurs when the transaction completes and the object is not visible in this transaction.

Update will also mark object to be created if the TIMESTAMP equals to NO_TIMESTAMP.

Parameters: engine The persistence engine molder The object's molder object The object to persist depended The master objects of the specified object to be created if exisit

Throws: DuplicateIdentityException An object with this identity already exists in persistent storage PersistenceException An error reported by the persistence engine ClassNotPersistenceCapableException The class is not persistent capable ObjectModifiedException Dirty checking mechanism may immediately report that the object was modified in the database during the long transaction.

writeLock

public void writeLock(Object object, int timeout)
Acquire a write lock on the object. Read locks are implicitly available when the object is queried. A write lock is only granted for objects that are created or deleted or for objects loaded in exclusive mode - this method can obtain such a lock explicitly. If the object already has a write lock in this transaction or a read lock in this transaction but no read lock in any other transaction, a write lock is obtained. If this object has a read lock in any other transaction this method will block until the other transaction will release its lock. If the specified timeout has elapsed or a deadlock has been detected, an exception will be thrown but the current lock will be retained.

Parameters: object The object to lock timeout Timeout waiting to acquire lock, specified in seconds, zero for no waiting, negative to use the default timeout for this transaction

Throws: ObjectNotPersistentException The object has not been queried or created in this transaction LockNotGrantedException Timeout or deadlock occured attempting to acquire lock on object PersistenceException An error reported by the persistence engine

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