Package com.helger.commons.id.factory

Class AbstractPersistingLongIDFactory

java.lang.Object

com.helger.commons.id.factory.AbstractPersistingLongIDFactory

All Implemented Interfaces:

IBaseIDFactory, ILongIDFactory

Direct Known Subclasses:

FileLongIDFactory

@ThreadSafe
public abstract class AbstractPersistingLongIDFactory
extends Object
implements ILongIDFactory

This implementation of ILongIDFactory reads IDs from a device. It does it by reserving a range of n IDs so that not each ID reservation requires IO. If only 1 ID is effectively used, the other n-1 IDs are lost and will never be assigned to any object again.

Author:

Philip Helger

Field Summary

Fields

Modifier and Type	Field	Description
protected SimpleLock	m_aLock

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	AbstractPersistingLongIDFactory(int nReserveCount)	Constructor.

Method Summary

Modifier and Type	Method	Description
boolean	equals(Object o)
long	getNewID()	Create a new unique long ID.
int	getReserveCount()
int	hashCode()
protected abstract long	readAndUpdateIDCounter(int nReserveCount)	Read the current ID from the device.
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

m_aLock

protected final SimpleLock m_aLock

Constructor Detail

AbstractPersistingLongIDFactory

protected AbstractPersistingLongIDFactory(@Nonnegative
                                          int nReserveCount)

Constructor.

Parameters:

nReserveCount - The number of IDs to reserve per persistence layer access. Must be > 0.

Method Detail

getReserveCount

@Nonnegative
public final int getReserveCount()

Returns:

The number of IDs to reserve, as provided in the constructor. Always > 0.

readAndUpdateIDCounter

@IsLocked(WRITE)
protected abstract long readAndUpdateIDCounter(@Nonnegative
                                               int nReserveCount)

Read the current ID from the device. In case the method is called for a non-initialized device, 0 should be returned.
The update should write the read value plus the passed reserve count back to the device. This method should perform an atomic read and update to avoid that ID can be reused.
Pseudo code:

 protected long readAndUpdateIDCounter (int nReserveCount)
 {
   final long nRead = FileIO.read (file);
   FileIO.write (file, nRead + nReserveCount);
   return nRead;
 }
 

Parameters:

nReserveCount - the number that should be added to the read value. Always > 0.

Returns:

0 if this method is called for a non-initialized device, the value read from the device otherwise or CGlobal.ILLEGAL_ULONG in case of an error.

getNewID

public final long getNewID()

Description copied from interface: ILongIDFactory

Create a new unique long ID.

Specified by:

getNewID in interface ILongIDFactory

Returns:

The newly created ID.

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object