Package org.apache.jackrabbit.oak.spi.commit

Class BackgroundObserver

java.lang.Object

org.apache.jackrabbit.oak.spi.commit.BackgroundObserver

All Implemented Interfaces:

Closeable, AutoCloseable, Observer

public class BackgroundObserver
extends Object
implements Observer, Closeable

An observer that uses a change queue and a background thread to forward content changes to another observer. The mechanism is designed so that the contentChanged(NodeState, CommitInfo) method will never block, regardless of the behavior of the other observer. If that observer blocks or is too slow to consume all content changes, causing the change queue to fill up, any further update will automatically be merged into just one external content change, causing potential loss of local commit information. To help prevent such cases, any sequential external content changes that the background observer thread has yet to process are optionally (see alwaysCollapseExternalEvents and oak.observation.alwaysCollapseExternal) automatically merged to just one change.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_QUEUE_SIZE

Constructor Summary

Constructors

Constructor	Description
BackgroundObserver(@NotNull Observer observer, @NotNull Executor executor)
BackgroundObserver(@NotNull Observer observer, @NotNull Executor executor, int queueLength)
BackgroundObserver(@NotNull Observer observer, @NotNull Executor executor, int queueLength, @NotNull Thread.UncaughtExceptionHandler exceptionHandler)

Method Summary

Modifier and Type	Method	Description
protected void	added(int queueSize)	Called when ever an item has been added to the queue
void	close()	Clears the change queue and signals the background thread to stop without making any further contentChanged(NodeState, CommitInfo) calls to the background observer.
void	contentChanged(@NotNull NodeState root, @NotNull CommitInfo info)	Observes a content change.
int	getMaxQueueLength()
@NotNull BackgroundObserverMBean	getMBean()
protected void	removed(int queueSize, long created)	Called when ever an item has been removed from the queue.

Methods inherited from class java.lang.Object

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

Field Details

DEFAULT_QUEUE_SIZE

public static final int DEFAULT_QUEUE_SIZE

See Also:

• Constant Field Values

Constructor Details

BackgroundObserver

public BackgroundObserver(@NotNull
 @NotNull Observer observer,
 @NotNull
 @NotNull Executor executor,
 int queueLength,
 @NotNull
 @NotNull Thread.UncaughtExceptionHandler exceptionHandler)

BackgroundObserver

public BackgroundObserver(@NotNull
 @NotNull Observer observer,
 @NotNull
 @NotNull Executor executor,
 int queueLength)

BackgroundObserver

public BackgroundObserver(@NotNull
 @NotNull Observer observer,
 @NotNull
 @NotNull Executor executor)

Method Details

added

protected void added(int queueSize)

Called when ever an item has been added to the queue

Parameters:

queueSize - size of the queue

removed

protected void removed(int queueSize,
 long created)

Called when ever an item has been removed from the queue.

Parameters:

queueSize - the size of the queue after the item was removed.

created - the time in milliseconds when the removed item was put into the queue.

getMaxQueueLength

public int getMaxQueueLength()

Returns:

The max queue length used for this observer's queue

close

public void close()

Clears the change queue and signals the background thread to stop without making any further contentChanged(NodeState, CommitInfo) calls to the background observer. If the thread is currently in the middle of such a call, then that call is allowed to complete; i.e. the thread is not forcibly interrupted. This method returns immediately without blocking to wait for the thread to finish.

After a call to this method further calls to contentChanged(NodeState, CommitInfo) will throw a IllegalStateException.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

getMBean

@NotNull
public @NotNull BackgroundObserverMBean getMBean()

contentChanged

public void contentChanged(@NotNull
 @NotNull NodeState root,
 @NotNull
 @NotNull CommitInfo info)

Description copied from interface: Observer

Observes a content change. See the Observer class javadocs and relevant repository and observer registration details for more information on when and how this method gets called.

Specified by:

contentChanged in interface Observer

Parameters:

root - root state of the repository

info - commit information

Throws:

IllegalStateException - if close() has already been called.