Class LockEngine
- java.lang.Object
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- org.exolab.castor.persist.LockEngine
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public final class LockEngine extends java.lang.Object
LockEngine is a gateway for all the ClassMolders of a persistence storage. It mantains dirty checking cache state and lock, and provides a thread safe enviroment for ClassMolder. LockEngine garantees 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...
It also provides caching for a persistence storage. Different
Cache
mechanisms can be specified.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.
Each class hierarchy gets its own cache, so caches can be controlled on a class-by-class basis.
- Version:
- $Revision: 8699 $ $Date: 2006-04-22 11:05:30 -0600 (Sat, 22 Apr 2006) $
- Author:
- Assaf Arkin, Thomas Yip, Bruce Snyder
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Constructor Summary
Constructors Constructor Description LockEngine(DatabaseContext databaseContext, ClassDescriptorResolver cdResolver, PersistenceFactory persistenceFactory)
Construct a new cache engine with the specified mapping table, persistence engine and the log interceptor.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
closeCaches()
Close all caches (to allow for resource clean-up).OID
create(TransactionContext tx, OID oid, java.lang.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(java.lang.Class cls)
Dump cached objects of specific type to output.void
expireCache()
Expires all objects of all types from cache.void
expireCache(java.lang.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.ClassMolder
getClassMolder(java.lang.Class cls)
Get classMolder which represents the given java data object class.ClassMolder
getClassMolder(java.lang.String classname)
ClassMolder
getClassMolderByNativeQuery(java.lang.String name)
Returns the ClassMolder instance that has a named native query associated with the name given.ClassMolder
getClassMolderByQuery(java.lang.String name)
Returns the ClassMolder instance that has a named query associated with the name given.ClassMolder
getClassMolderWithDependent(java.lang.Class cls)
ClassMolder
getClassMolderWithDependent(java.lang.String classname)
DatabaseContext
getDatabaseContext()
Persistence
getPersistence(java.lang.Class cls)
java.util.HashMap<javax.transaction.xa.Xid,TransactionContext>
getXATransactions()
Returns an association between Xid and transactions contexts.boolean
isCached(java.lang.Class cls, OID oid)
Provides information about whether an object of Class cls with identity iod is currently cached.boolean
isLocked(java.lang.Class cls, OID oid)
void
load(AbstractTransactionContext tx, OID paramoid, 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, java.lang.Object object)
Mark an object and its related or dependent object to be created.void
markDelete(TransactionContext tx, OID oid, java.lang.Object object, int timeout)
OID
preStore(TransactionContext tx, OID oid, java.lang.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, java.lang.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, java.lang.Object object)
boolean
update(TransactionContext tx, OID oid, java.lang.Object object, AccessMode suggestedAccessMode, int timeout)
Updates an existing object to this engine.void
updateCache(TransactionContext tx, OID oid, java.lang.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.
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Constructor Detail
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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 interceptor.- Parameters:
databaseContext
-cdResolver
-persistenceFactory
- Factory for creating persistence engines for each object described in the map.- Throws:
MappingException
- Indicate that one of the mappings is invalid
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Method Detail
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getDatabaseContext
public DatabaseContext getDatabaseContext()
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getClassMolder
public ClassMolder getClassMolder(java.lang.Class cls)
Get classMolder which represents the given java data object class. Dependent class will not be returned to avoid persistenting a dependent class without.- Parameters:
cls
- Class instance for whic a class molder should be returned.- Returns:
- The class molder for the specified class.
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getClassMolder
public ClassMolder getClassMolder(java.lang.String classname)
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getClassMolderWithDependent
public ClassMolder getClassMolderWithDependent(java.lang.Class cls)
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getClassMolderWithDependent
public ClassMolder getClassMolderWithDependent(java.lang.String classname)
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getClassMolderByQuery
public ClassMolder getClassMolderByQuery(java.lang.String name)
Returns the ClassMolder instance that has a named query associated with the name given.- Parameters:
name
- Name of a named query.- Returns:
- ClassMolder instance associated with the named query.
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getClassMolderByNativeQuery
public ClassMolder getClassMolderByNativeQuery(java.lang.String name)
Returns the ClassMolder instance that has a named native query associated with the name given.- Parameters:
name
- Name of a named query.- Returns:
- ClassMolder instance associated with the named native query.
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getPersistence
public Persistence getPersistence(java.lang.Class cls)
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load
public void load(AbstractTransactionContext tx, OID paramoid, ProposedEntity proposedObject, AccessMode suggestedAccessMode, int timeout, QueryResults results, ClassMolder paramMolder, Identity identity) throws PersistenceException, java.lang.InstantiationException, java.lang.IllegalAccessException, java.lang.ClassNotFoundException
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 contextparamoid
- The identity of the object to loadproposedObject
- The type of the object to loadsuggestedAccessMode
- The desired access modetimeout
- The timeout waiting to acquire a lock on the object (specified in seconds)- Throws:
ObjectNotFoundException
- The object was not found in persistent storageLockNotGrantedException
- Timeout or deadlock occured attempting to acquire lock on objectPersistenceException
- An error reported by the persistence engineClassNotPersistenceCapableException
- The class is not persistent capableObjectDeletedWaitingForLockException
- The object has been deleted, but is waiting for a lock.java.lang.InstantiationException
java.lang.IllegalAccessException
java.lang.ClassNotFoundException
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markCreate
public void markCreate(TransactionContext tx, OID oid, java.lang.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 occured attempting to acquire lock on object.
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create
public OID create(TransactionContext tx, OID oid, java.lang.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 contextoid
- The identity of the object, or nullobject
- The newly created object- Returns:
- The object's OID
- Throws:
DuplicateIdentityException
- An object with this identity already exists in persistent storagePersistenceException
- An error reported by the persistence engineClassNotPersistenceCapableException
- The class is not persistent capable
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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 contextoid
- The object's identity- Throws:
PersistenceException
- An error reported by the persistence engine
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markDelete
public void markDelete(TransactionContext tx, OID oid, java.lang.Object object, int timeout) throws PersistenceException
- Throws:
PersistenceException
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update
public boolean update(TransactionContext tx, OID oid, java.lang.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 contextoid
- The object's identityobject
- The objectsuggestedAccessMode
- The desired access modetimeout
- The timeout waiting to acquire a lock on the object (specified in seconds)- Returns:
- The object's OID
- Throws:
ObjectNotFoundException
- The object was not found in persistent storageLockNotGrantedException
- Timeout or deadlock occured attempting to acquire lock on objectPersistenceException
- An error reported by the persistence engineClassNotPersistenceCapableException
- The class is not persistent capableObjectModifiedException
- Dirty checking mechanism may immediately report that the object was modified in the database during the long transaction.ObjectDeletedWaitingForLockException
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preStore
public OID preStore(TransactionContext tx, OID oid, java.lang.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 contextoid
- The object's identityobject
- The object to storetimeout
- The timeout waiting to acquire a lock on the object (specified in seconds)- Returns:
- The object's OID if stored, null if ignored
- Throws:
LockNotGrantedException
- Timeout or deadlock occured attempting to acquire lock on objectObjectDeletedException
- The object has been deleted from persistent storageObjectModifiedException
- The object has been modified in persistent storage since it was loaded, the memory image is no longer validDuplicateIdentityException
- An object with this identity already exists in persistent storagePersistenceException
- An error reported by the persistence engine
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store
public void store(TransactionContext tx, OID oid, java.lang.Object object) throws PersistenceException
- Throws:
PersistenceException
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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 contextoid
- The object's OIDtimeout
- The timeout waiting to acquire a lock on the object (specified in seconds)- Throws:
LockNotGrantedException
- Timeout or deadlock occured attempting to acquire lock on objectObjectDeletedException
- The object has been deleted from persistent storagePersistenceException
- An error reported by the persistence engine
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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 contextoid
- The object's OIDtimeout
- The timeout waiting to acquire a lock on the object (specified in seconds)- Throws:
LockNotGrantedException
- Timeout or deadlock occured attempting to acquire lock on object persistent storage
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revertObject
public void revertObject(TransactionContext tx, OID oid, java.lang.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 contextoid
- The object's oidobject
- The object into which to copy- Throws:
PersistenceException
- An error reported by the persistence engine obtaining a dependent object
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updateCache
public void updateCache(TransactionContext tx, OID oid, java.lang.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 fromstore(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 contextoid
- The object's oidobject
- The object to copy from
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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 contextoid
- The object OID
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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 contextoid
- The object OID
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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 contextoid
- The object OIDtimeout
- 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:
LockNotGrantedException
- Timeout or deadlock occured attempting to acquire lock on objectPersistenceException
- An error reported by the persistence engineClassNotPersistenceCapableException
- The class is not persistent capableObjectModifiedException
- Dirty checking mechanism may immediately report that the object was modified in the database during the long transaction.ObjectDeletedException
- Object has been deleted from the persistence store.
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expireCache
public void expireCache(java.lang.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.
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expireCache
public void expireCache()
Expires all objects of all types from cache.
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dumpCache
public void dumpCache()
Dump cached objects of all types to output.
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closeCaches
public void closeCaches()
Close all caches (to allow for resource clean-up).
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dumpCache
public void dumpCache(java.lang.Class cls)
Dump cached objects of specific type to output.- Parameters:
cls
- A class type.
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getXATransactions
public java.util.HashMap<javax.transaction.xa.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.
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isCached
public boolean isCached(java.lang.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.
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isLocked
public boolean isLocked(java.lang.Class cls, OID oid)
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