org.garret.perst
Class PersistentResource

java.lang.Object
  org.garret.perst.Persistent
      org.garret.perst.PersistentResource

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, java.lang.Cloneable, ICloneable, IPersistent, IResource

Direct Known Subclasses:

L2ListElem, PersistentCollection, PersistentString, Version, VersionHistory

public class PersistentResource
extends Persistent
implements IResource

Base class for persistent capable objects supporting locking

See Also:

Serialized Form

Constructor Summary

PersistentResource()

PersistentResource(Storage storage)

Method Summary

void	exclusiveLock() Lock persistent object in exclusive mode.
boolean	exclusiveLock(long timeout) Lock persistent object in exclusive mode.
void	reset() Reset resource to original state.
void	sharedLock() Lock persistent object in shared mode.
boolean	sharedLock(long timeout) Lock persistent object in shared mode.
void	unlock() Remove granted lock.

Methods inherited from class org.garret.perst.Persistent

assignOid, clone, deallocate, equals, getOid, getStorage, hashCode, invalidate, isDeleted, isModified, isPersistent, isRaw, load, loadAndModify, makePersistent, modify, onLoad, onStore, readExternal, recursiveLoading, store, writeExternal

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PersistentResource

public PersistentResource()

PersistentResource

public PersistentResource(Storage storage)

Method Detail

exclusiveLock

public void exclusiveLock()

Description copied from interface: IResource

Lock persistent object in exclusive mode. Only one thread can lock object in exclusive mode at each moment of time. Shared or exclusive lock requests of other threads will be blocked until this lock is released. shared locks on this objects, but not exclusive lock can be set until this lock is released.
This lock is reentrant, so thread owning the lock can successfully retrieve the lock many times (and correspondent number of unlocks is needed to release the lock).
Locking the object doesn't prevent other threads from accessing the object - it only has influence on sharedLock and exclusiveLock methods. So programmer should set proper lock before accessing the object in multithreaded application.
Only persistent object (object which were assigned to the the storage either implicitly by saving some other persistent object referencing this object, either explicitly by Storage.makeObjectPersistent method.

Specified by:

exclusiveLock in interface IResource

exclusiveLock

public boolean exclusiveLock(long timeout)

Description copied from interface: IResource

Lock persistent object in exclusive mode. Only one thread can lock object in exclusive mode at each moment of time. Shared or exclusive lock requests of other threads will be blocked until this lock is released. shared locks on this objects, but not exclusive lock can be set until this lock is released.
This lock is reentrant, so thread owning the lock can successfully retrieve the lock many times (and correspondent number of unlocks is needed to release the lock).
Locking the object doesn't prevent other threads from accessing the object - it only has influence on sharedLock and exclusiveLock methods. So programmer should set proper lock before accessing the object in multithreaded application.
Only persistent object (object which were assigned to the the storage either implicitly by saving some other persistent object referencing this object, either explicitly by Storage.makeObjectPersistent method.

Specified by:

exclusiveLock in interface IResource

Parameters:

timeout - timeout of operation in milliseconds. If timeout is 0 and lock can not be granted, the request will fail immediately. Otherwise the system will try to grant lock within specified amount of time.

Returns:

true if lock is successfully granted

false if lock can not be granted within specified time

reset

public void reset()

Description copied from interface: IResource

Reset resource to original state. Wakrup all threads waiting for this resource.

Specified by:

reset in interface IResource

sharedLock

public void sharedLock()

Description copied from interface: IResource

Lock persistent object in shared mode. Other threads will be able to set their shared locks on this objects, but not exclusive lock can be set until this lock is released.
Upgrading of the lock is not possible (thread having read lock can not upgrade it to exclusive lock). It is done to prevent possible deadlocks caused by lock updates. But locks are reentrant - so thread can request the same lock many times (and correspondent number of unlocks is needed to release the lock).
Locking the object doesn't prevent other threads from accessing the object - it only has influence on sharedLock and exclusiveLock methods. So programmer should set proper lock before accessing the object in multithreaded application.
If object is concurrently accessed by several threads in read-only mode, then explicit locking of this object is not needed, because language API provides consistent retrieving of objects itself.
Only persistent object (object which were assigned to the the storage either implicitly by saving some other persistent object referencing this object, either explicitly by Storage.makeObjectPersistent method.

Specified by:

sharedLock in interface IResource

sharedLock

public boolean sharedLock(long timeout)

Description copied from interface: IResource

Lock persistent object in shared mode. Other threads will be able to set their shared locks on this objects, but not exclusive lock can be set until this lock is released.
Upgrading of the lock is not possible (thread having read lock can not upgrade it to exclusive lock). It is done to prevent possible deadlocks caused by lock updates. But locks are reentrant - so thread can request the same lock many times (and correspondent number of unlocks is needed to release the lock).
Locking the object doesn't prevent other threads from accessing the object - it only has influence on sharedLock and exclusiveLock methods. So programmer should set proper lock before accessing the object in multithreaded application.
If object is concurrently accessed by several threads in read-only mode, then explicit locking of this object is not needed, because language API provides consistent retrieving of objects itself.
Only persistent object (object which were assigned to the the storage either implicitly by saving some other persistent object referencing this object, either explicitly by Storage.makeObjectPersistent method.

Specified by:

sharedLock in interface IResource

Parameters:

timeout - timeout of operation in milliseconds. If timeout is 0 and lock can not be granted, the request will fail immediately. Otherwise the system will try to grant lock within specified amount of time.

Returns:

true if lock is successfully granted

false if lock can not be granted within specified time

unlock

public void unlock()

Description copied from interface: IResource

Remove granted lock. If lock was requested several times by one thread, then correspondent number of unlocks is needed to release the lock.

Specified by:

unlock in interface IResource