com.hazelcast.spi.merge

Class RingbufferMergeData

java.lang.Object

com.hazelcast.spi.merge.RingbufferMergeData

All Implemented Interfaces:

Iterable<Object>

public class RingbufferMergeData
extends Object
implements Iterable<Object>

A ringbuffer implementation holding data involved in split-brain healing.

Since:

3.10

See Also:

RingbufferMergingValueImpl

Constructor Summary

Constructors

Constructor and Description
RingbufferMergeData(int capacity)
RingbufferMergeData(com.hazelcast.ringbuffer.impl.Ringbuffer<Object> ringbuffer)

Method Summary

Modifier and Type	Method and Description
long	add(Object item) Adds an item to the tail of the ringbuffer.
void	clear() Clears the data in the ringbuffer.
int	getCapacity() Returns the capacity of this ringbuffer.
long	getHeadSequence() Returns the sequence of the head.
Object[]	getItems() Returns the array representing this ringbuffer.
long	getTailSequence() Returns the sequence of the tail.
Iterator<Object>	iterator() Returns a read-only iterator.
<E> E	read(long sequence) Reads one item from the ringbuffer.
void	set(long seq, Object data) Sets the item at the given sequence.
void	setHeadSequence(long sequence) Sets the head sequence.
void	setTailSequence(long sequence) Sets the tail sequence.
int	size() Returns number of items in the ringbuffer (meaning the number of items between the getHeadSequence() and getTailSequence()).

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Detail

RingbufferMergeData

public RingbufferMergeData(int capacity)

RingbufferMergeData

public RingbufferMergeData(com.hazelcast.ringbuffer.impl.Ringbuffer<Object> ringbuffer)

Method Detail

getTailSequence

public long getTailSequence()

Returns the sequence of the tail. The tail is the side of the ringbuffer where the items are added to.

The initial value of the tail is -1.

Returns:

the sequence of the tail

setTailSequence

public void setTailSequence(long sequence)

Sets the tail sequence. The tail sequence cannot be less than headSequence() - 1.

Parameters:

sequence - the new tail sequence

Throws:

IllegalArgumentException - if the target sequence is less than headSequence() - 1

See Also:

getHeadSequence()

getHeadSequence

public long getHeadSequence()

Returns the sequence of the head. The head is the side of the ringbuffer where the oldest items in the ringbuffer are found.

If the RingBuffer is empty, the head will be one more than the getTailSequence().

The initial value of the head is 0 (1 more than tail).

Returns:

the sequence of the head

setHeadSequence

public void setHeadSequence(long sequence)

Sets the head sequence. The head sequence cannot be larger than tailSequence() + 1.

Parameters:

sequence - the new head sequence

Throws:

IllegalArgumentException - if the target sequence is greater than tailSequence() + 1

See Also:

getTailSequence()

getCapacity

public int getCapacity()

Returns the capacity of this ringbuffer.

Returns:

the capacity

size

public int size()

Returns number of items in the ringbuffer (meaning the number of items between the getHeadSequence() and getTailSequence()).

Returns:

the size

add

public long add(Object item)

Adds an item to the tail of the ringbuffer. If there is no space in the ringbuffer, the add will overwrite the oldest item in the ringbuffer. The method allows null values.

The returned value is the sequence of the added item. Using this sequence you can read the added item.

Using the sequence as ID

This sequence will always be unique for this ringbuffer instance so it can be used as a unique ID generator if you are publishing items on this ringbuffer. However you need to take care of correctly determining an initial ID when any node uses the ringbuffer for the first time. The most reliable way to do that is to write a dummy item into the ringbuffer and use the returned sequence as initial ID. On the reading side, this dummy item should be discard. Please keep in mind that this ID is not the sequence of the item you are about to publish but from a previously published item. So it can't be used to find that item.

Parameters:

item - the item to add

Returns:

the sequence of the added item

read

public <E> E read(long sequence)

Reads one item from the ringbuffer.

Type Parameters:

E - ringbuffer item type

Parameters:

sequence - the sequence of the item to read

Returns:

the ringbuffer item

Throws:

StaleSequenceException - if the sequence is smaller then getHeadSequence() or larger than getTailSequence()

set

public void set(long seq,
                Object data)

Sets the item at the given sequence. The method allows null data.

Parameters:

seq - the target sequence

data - the data to be set

clear

public void clear()

Clears the data in the ringbuffer.

getItems

public Object[] getItems()

Returns the array representing this ringbuffer.

Items at the beginning of this array may have higher sequence IDs than items at the end of this array. This means that this array is not sorted by sequence ID and the index of the item in this array must be calculated using the sequence and the modulo of the array.

iterator

public Iterator<Object> iterator()

Returns a read-only iterator. Mutation methods will throw a UnsupportedOperationException.

Specified by:

iterator in interface Iterable<Object>