Class BackgroundCleaner

java.lang.Object

org.apache.derby.impl.services.cache.BackgroundCleaner

All Implemented Interfaces:

Serviceable

final class BackgroundCleaner
extends Object
implements Serviceable

A background cleaner that ConcurrentCache can use to clean Cacheables asynchronously in a background instead of synchronously in the user threads. It is normally used by the replacement algorithm in order to make dirty Cacheables clean and evictable in the future. When the background cleaner is asked to clean an item, it puts the item in a queue and requests to be serviced by a DaemonService running in a separate thread.

Field Summary

Fields

Modifier and Type	Field	Description
private final ConcurrentCache	cacheManager	The cache manager owning this cleaner.
private final int	clientNumber	Subscription number for this Serviceable.
private final DaemonService	daemonService	The service thread which performs the clean operations.
private final ArrayBlockingQueue<CacheEntry>	queue	A queue of cache entries that need to be cleaned.
private final AtomicBoolean	scheduled	Flag which tells whether the cleaner has a still unprocessed job scheduled with the daemon service.
private boolean	shrink	Flag which tells whether the cleaner should try to shrink the cache the next time it wakes up.

Fields inherited from interface Serviceable

DONE, REQUEUE

Constructor Summary

Constructors

Constructor	Description
BackgroundCleaner(ConcurrentCache cache, DaemonService daemon, int queueSize)	Create a background cleaner instance and subscribe it to a daemon service.

Method Summary

Modifier and Type	Method	Description
int	performWork(ContextManager context)	Clean the first entry in the queue.
private void	requestService()	Notify the daemon service that the cleaner needs to be serviced.
(package private) boolean	scheduleClean(CacheEntry entry)	Try to schedule a clean operation in the background cleaner.
(package private) void	scheduleShrink()	Request that the cleaner tries to shrink the cache the next time it wakes up.
boolean	serviceASAP()	Indicate that we want to be serviced ASAP.
boolean	serviceImmediately()	Indicate that we don't want the work to happen immediately in the user thread.
(package private) void	unsubscribe()	Stop subscribing to the daemon service.

Methods inherited from class Object

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

Field Details

daemonService

private final DaemonService daemonService

The service thread which performs the clean operations.

clientNumber

private final int clientNumber

Subscription number for this Serviceable.

scheduled

private final AtomicBoolean scheduled

Flag which tells whether the cleaner has a still unprocessed job scheduled with the daemon service. If this flag is true, calls to serviceNow() won't result in the cleaner being serviced.

queue

private final ArrayBlockingQueue<CacheEntry> queue

A queue of cache entries that need to be cleaned.

shrink

private volatile boolean shrink

Flag which tells whether the cleaner should try to shrink the cache the next time it wakes up.

cacheManager

private final ConcurrentCache cacheManager

The cache manager owning this cleaner.

Constructor Details

BackgroundCleaner

BackgroundCleaner(ConcurrentCache cache,
 DaemonService daemon,
 int queueSize)

Create a background cleaner instance and subscribe it to a daemon service.

Parameters:

cache - the cache manager that owns the cleaner

daemon - the daemon service which perfoms the work

queueSize - the maximum number of entries to keep in the queue (must be greater than 0)

Method Details

scheduleClean

boolean scheduleClean(CacheEntry entry)

Try to schedule a clean operation in the background cleaner.

Parameters:

entry - the entry that needs to be cleaned

Returns:

true if the entry has been scheduled for clean, false if the background cleaner can't clean the entry (its queue is full)

scheduleShrink

void scheduleShrink()

Request that the cleaner tries to shrink the cache the next time it wakes up.

requestService

private void requestService()

Notify the daemon service that the cleaner needs to be serviced.

unsubscribe

void unsubscribe()

Stop subscribing to the daemon service.

performWork

public int performWork(ContextManager context)
                throws StandardException

Clean the first entry in the queue. If there is more work, re-request service from the daemon service.

Specified by:

performWork in interface Serviceable

Parameters:

context - ignored

Returns:

status for the performed work (normally Serviceable.DONE)

Throws:

StandardException - if Cacheable.clean() fails

serviceASAP

public boolean serviceASAP()

Indicate that we want to be serviced ASAP.

Specified by:

serviceASAP in interface Serviceable

Returns:

true

serviceImmediately

public boolean serviceImmediately()

Indicate that we don't want the work to happen immediately in the user thread.

Specified by:

serviceImmediately in interface Serviceable

Returns:

false