org.apache.excalibur.event.impl
Class LossyMultiCastSink

java.lang.Object
  org.apache.excalibur.event.impl.LossyMultiCastSink

All Implemented Interfaces:

Sink

public class LossyMultiCastSink

extends java.lang.Object

implements Sink

This is a org.apache.excalibur.event.seda.event.Sink implementation that multicasts enqueue operations to the contained and concrete sink objects. Compared to the regular org.apache.excalibur.event.seda.event.impl.MultiCastSink this sink works in that it delivers zero, one or more sinks. It can be configured to fail when less than one sink was delivered to.

Version:

$Revision: 1.4 $

Author:

Avalon Development Team

Field Summary

Fields inherited from interface org.apache.excalibur.event.Sink

ROLE

Constructor Summary

LossyMultiCastSink(java.util.Collection sinks)
This constructor creates a failure tolerant sink based on the collection of sink arrays.

LossyMultiCastSink(java.util.Collection sinks, boolean oneSuccess)
This constructor creates a failure tolerant sink based on the collection of sink arrays.

Method Summary

int	canAccept() Returns the number of elements it can currently accept.
void	enqueue(java.lang.Object element) Enqueues the given element onto the Sink.
void	enqueue(java.lang.Object[] elements) Given an array of elements, atomically enqueues all of the elements in the array.
boolean	isFull() Returns true if this sink has reached its threshold; false otherwise.
int	maxSize() Returns the length threshold of the sink.
PreparedEnqueue	prepareEnqueue(java.lang.Object[] elements) Support for transactional enqueue.
int	size() Returns the number of elements waiting in this Sink.
boolean	tryEnqueue(java.lang.Object element) Tries to enqueue an event, but instead of throwing exceptions, it returns a boolean value of whether the attempt was successful.

Methods inherited from class java.lang.Object

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

Constructor Detail

LossyMultiCastSink

public LossyMultiCastSink(java.util.Collection sinks)

This constructor creates a failure tolerant sink based on the collection of sink arrays. None of the enqueue operations must succeed.

Parameters:

sinks - A collection of sink arrays for each stage.

Since:

May 16, 2002

LossyMultiCastSink

public LossyMultiCastSink(java.util.Collection sinks,
                          boolean oneSuccess)

This constructor creates a failure tolerant sink based on the collection of sink arrays. The additional boolean flag describes whether at least one or none of the enqueue operations must succeed.

Parameters:

sinks - A collection of sink arrays for each stage.

Since:

May 16, 2002

Method Detail

canAccept

public int canAccept()

Description copied from interface: Sink

Returns the number of elements it can currently accept. This is typically the difference between size() and maxSize(). It will return -1 if the sink is unbounded.

Specified by:

canAccept in interface Sink

Returns:

the number of elements the Sink can accept

See Also:

Sink.canAccept()

isFull

public boolean isFull()

Description copied from interface: Sink

Returns true if this sink has reached its threshold; false otherwise. Like maxSize(), this is also informational, and isFull() returning false does not guarantee that future enqueue operations will succeed. Clearly, isFull() returning true does not guarantee that they will fail, since the Sink may be serviced in the meantime.

Specified by:

isFull in interface Sink

Returns:

true if the Sink is full

See Also:

Sink.isFull()

maxSize

public int maxSize()

Description copied from interface: Sink

Returns the length threshold of the sink. This is for informational purposes only; an implementation may allow more (or fewer) new entries to be enqueued than maxSize() - size(). This may be the case, for example, if the sink implements some form of dynamic thresholding, and does not always accurately report maxSize().

Specified by:

maxSize in interface Sink

Returns:

-1 if the sink has no length threshold.

See Also:

Sink.maxSize()

enqueue

public void enqueue(java.lang.Object element)
             throws SinkException

Description copied from interface: Sink

Enqueues the given element onto the Sink.

Specified by:

enqueue in interface Sink

Parameters:

element - The elements to enqueue

Throws:

SinkException

See Also:

Sink.enqueue(Object)

enqueue

public void enqueue(java.lang.Object[] elements)
             throws SinkException

Description copied from interface: Sink

Given an array of elements, atomically enqueues all of the elements in the array. This guarantees that no other thread can interleave its own elements with those being inserted from this array. The implementation must enqueue all of the elements or none of them; if a SinkFullException or SinkClosedException is thrown, none of the elements will have been enqueued.

Specified by:

enqueue in interface Sink

Parameters:

elements - The element array to enqueue

Throws:

SinkException

See Also:

Sink.enqueue(Object[])

tryEnqueue

public boolean tryEnqueue(java.lang.Object element)

Description copied from interface: Sink

Tries to enqueue an event, but instead of throwing exceptions, it returns a boolean value of whether the attempt was successful.

Specified by:

tryEnqueue in interface Sink

Parameters:

element - The element to attempt to enqueue

Returns:

true if successful, false if not.

See Also:

Sink.tryEnqueue(Object)

prepareEnqueue

public PreparedEnqueue prepareEnqueue(java.lang.Object[] elements)
                               throws SinkException

Description copied from interface: Sink

Support for transactional enqueue.

This method allows a client to provisionally enqueue a number of elements onto the queue, and then later commit the enqueue (with a commitEnqueue call), or abort (with an abortEnqueue call). This mechanism can be used to perform "split-phase" enqueues, where a client first enqueues a set of elements on the queue and then performs some work to "fill in" those elements before performing a commit. This can also be used to perform multi-queue transactional enqueue operations, with an "all-or-nothing" strategy for enqueueing events on multiple Sinks.

This method would generally be used in the following manner:

   PreparedEnqueue enqueue = sink.prepareEnqueue(someElements);
   if (canCommit) {
     enqueue.commit();
   } else {
     enqueue.abort();
   }
 

Note that this method does not protect against "dangling prepares" -- that is, a prepare without an associated commit or abort operation. This method should be used with care. In particular, be sure that all code paths (such as exceptions) after a prepare include either a commit or an abort.

Specified by:

prepareEnqueue in interface Sink

Parameters:

elements - The element array to provisionally enqueue

Returns:

A PreparedEnqueue that may be used to commit or abort the provisional enqueue

Throws:

SinkException

See Also:

Sink.prepareEnqueue(Object[])

size

public int size()

Description copied from interface: Sink

Returns the number of elements waiting in this Sink.

Important: The contract for this method was updated to account for any elements that were prepared for enqueueing. It provides a more predictable and consistent environment, as well as making it easier for EnqueuePredicates to account for those elements.

Specified by:

size in interface Sink

Returns:

the number of elements in the Sink

See Also:

Sink.size()