com.helger.commons.id.factory

Class AbstractPersistingIntIDFactory

java.lang.Object

com.helger.commons.id.factory.AbstractPersistingIntIDFactory

All Implemented Interfaces:

IBaseIDFactory, IIntIDFactory

Direct Known Subclasses:

FileIntIDFactory

@ThreadSafe
public abstract class AbstractPersistingIntIDFactory
extends Object
implements IIntIDFactory

This implementation of IIntIDFactory 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 and Description
protected SimpleLock	m_aLock

Constructor Summary

Constructors

Constructor and Description
AbstractPersistingIntIDFactory(int nReserveCount) Constructor.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object o)
int	getNewID() Create a new unique integer ID.
int	getReserveCount()
int	hashCode()
protected abstract int	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

AbstractPersistingIntIDFactory

public AbstractPersistingIntIDFactory(@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(value=WRITE)
protected abstract int 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 int readAndUpdateIDCounter (int nReserveCount)
 {
   final int 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_UINT in case of an error.

getNewID

public final int getNewID()

Description copied from interface: IIntIDFactory

Create a new unique integer ID.

Specified by:

getNewID in interface IIntIDFactory

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