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org.apache.derby.impl.services.cache
Class CachedItem  

java.lang.Object
  org.apache.derby.impl.services.cache.CachedItem

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public final class CachedItem

extends java.lang.Object

A generic class to represent the cache related infomation of a cached object (Cacheable).

        The relationship between isValid and settingIdentity can be explain by the
        following life cycle of a cached item.

        Stage		   1	2	3
        ----------------------
        isValid	        F	T	T	
        settingIdentity	X	T	F

        In Stage 1, the CachedItem is created but it is invalid and has an entry
        that is just a holder object with no identity.

        In Stage 2, the identity has been set and the item is being created or
        being faulted into the cache.

        In Stage 3, the item found in the CachedItem entry
        

Remove is set if this item is being removed out of existance, not just being evicted from the cache. When the last referece to it release it from the cache, it will be removed.
RecentlyUsed is set whenever this item is accessed (via a keep() call). It is reset by the clockHand as it sweeps around the cache looking for victims to evict.

MT - must be MT-safe and work with cache manager. Every method that access (set or get) instance variables is synchronized on the cached item object. The following method waits so it should not be called by the cache manager inside a sync block: clean(), waitFor(), create(), remove(). (RESOLVE: need to move these from the cache manager to here)

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Field Summary
private  org.apache.derby.iapi.services.cache.Cacheable	entry           The Cacheable object being represented.
private  int	keepCount           The current keep count on the entry.
private static int	RECENTLY_USED
private static int	REMOVE_OK
private static int	REMOVE_REQUESTED
private static int	SETTING_IDENTITY
private  int	state           Does entry (the Cacheable) have an identity.
private static int	VALID

 

Constructor Summary

CachedItem()           Create a CachedItem in the not valid state.

 

Method Summary
void	clean(boolean forRemove)           Clean the cached object
org.apache.derby.iapi.services.cache.Cacheable	getEntry()           Get the cached object.
boolean	isKept()           Is the cached object kept?
boolean	isValid()           Does the cached object have a valid identity.
void	keepAfterSearch()           Keep the cached object after a search.
void	keepForClean()
void	keepForCreate()
void	notifyRemover()
boolean	recentlyUsed()           Has the cached object been referenced (kept) since the last sweep of the clock hand?
void	remove(boolean removeNow)
void	setRemoveState()           Set the state of the to-be removed flag.
void	settingIdentityComplete()
void	setUsed(boolean flag)           The clock hand has swept past this entry.
void	setValidState(boolean flag)           Set the valid state of the cached object.
org.apache.derby.iapi.services.cache.Cacheable	takeOnIdentity(org.apache.derby.iapi.services.cache.CacheManager cm, org.apache.derby.iapi.services.cache.CacheableFactory holderFactory, java.lang.Object key, boolean forCreate, java.lang.Object createParameter)           Make entry (the Cacheable) take on a new identity.
boolean	unkeep()           Unkeep the cached object.
void	unkeepForCreate()
org.apache.derby.iapi.services.cache.Cacheable	use()           Allow use of the cacheable entry.

 

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Field Detail

VALID

private static final int VALID

See Also:

Constant Field Values

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REMOVE_REQUESTED

private static final int REMOVE_REQUESTED

See Also:

Constant Field Values

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SETTING_IDENTITY

private static final int SETTING_IDENTITY

See Also:

Constant Field Values

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REMOVE_OK

private static final int REMOVE_OK

See Also:

Constant Field Values

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RECENTLY_USED

private static final int RECENTLY_USED

See Also:

Constant Field Values

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state

private int state

Does entry (the Cacheable) have an identity.
MT - single thread required : synchronization provided by cache manager.

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keepCount

private int keepCount

The current keep count on the entry.
MT - single thread required : synchronization provided by cache manager.

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entry

private org.apache.derby.iapi.services.cache.Cacheable entry

The Cacheable object being represented.
Mutable - content dynamic

Constructor Detail

CachedItem

public CachedItem()

Create a CachedItem in the not valid state.

Method Detail

keepAfterSearch

public void keepAfterSearch()

Keep the cached object after a search.

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keepForCreate

public void keepForCreate()

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unkeepForCreate

public void unkeepForCreate()

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keepForClean

public void keepForClean()

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unkeep

public boolean unkeep()

Unkeep the cached object.

MT - not synchronized, only modified single threaded by the cache manager

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isKept

public final boolean isKept()

Is the cached object kept?

MT - not synchronized, only accessed single threaded by the cache manager

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clean

public void clean(boolean forRemove)
           throws org.apache.derby.iapi.error.StandardException

Clean the cached object

MT -
The wait will not release the lock on the cache manager, so the cache manager should not waitfor clean inside a sync block or the whole cache will freeze

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setRemoveState

public void setRemoveState()

Set the state of the to-be removed flag.

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isValid

public final boolean isValid()

Does the cached object have a valid identity.

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setValidState

public void setValidState(boolean flag)

Set the valid state of the cached object.

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getEntry

public org.apache.derby.iapi.services.cache.Cacheable getEntry()

Get the cached object.

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takeOnIdentity

public org.apache.derby.iapi.services.cache.Cacheable takeOnIdentity(org.apache.derby.iapi.services.cache.CacheManager cm,
                                                                     org.apache.derby.iapi.services.cache.CacheableFactory holderFactory,
                                                                     java.lang.Object key,
                                                                     boolean forCreate,
                                                                     java.lang.Object createParameter)
                                                              throws org.apache.derby.iapi.error.StandardException

Make entry (the Cacheable) take on a new identity.

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settingIdentityComplete

public void settingIdentityComplete()

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use

public org.apache.derby.iapi.services.cache.Cacheable use()
                                                   throws org.apache.derby.iapi.error.StandardException

Allow use of the cacheable entry.

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remove

public void remove(boolean removeNow)
            throws org.apache.derby.iapi.error.StandardException

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notifyRemover

public void notifyRemover()

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setUsed

public void setUsed(boolean flag)

The clock hand has swept past this entry.

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recentlyUsed

public boolean recentlyUsed()

Has the cached object been referenced (kept) since the last sweep of the clock hand?

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> org >> apache >> derby >> impl >> services >> [ cache overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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