com.hazelcast.ringbuffer.impl

Interface Ringbuffer<E>

Type Parameters:

E - the type of the data stored in the ringbuffer

All Superinterfaces:

Iterable<E>

All Known Implementing Classes:

ArrayRingbuffer

public interface Ringbuffer<E>
extends Iterable<E>

The Ringbuffer is responsible for storing the actual content of a ringbuffer.

Method Summary

Modifier and Type	Method and Description
long	add(E item) Adds an item to the tail of the ringbuffer.
void	checkBlockableReadSequence(long readSequence) Check if the sequence can be read from the ringbuffer or if the sequence is of the next item to be added into the ringbuffer.
void	checkReadSequence(long sequence) Check if the sequence can be read from the ringbuffer.
void	clear() Clears the data in the ringbuffer.
long	getCapacity() Returns the capacity of this ringbuffer.
E[]	getItems() Returns the array representing this ringbuffer.
long	headSequence() Returns the sequence of the head.
boolean	isEmpty() Checks if the ringbuffer is empty.
long	peekNextTailSequence() Returns the next sequence which the tail will be at after the next item is added.
E	read(long sequence) Reads one item from the ringbuffer.
void	set(long seq, E data) Sets the item at the given sequence.
void	setHeadSequence(long sequence) Sets the head sequence.
void	setTailSequence(long tailSequence) Sets the tail sequence.
long	size() Returns number of items in the ringbuffer (meaning the number of items between the headSequence() and tailSequence()).
long	tailSequence() Returns the sequence of the tail.

Methods inherited from interface java.lang.Iterable

forEach, iterator, spliterator

Method Detail

getCapacity

long getCapacity()

Returns the capacity of this ringbuffer.

Returns:

the capacity

size

long size()

Returns number of items in the ringbuffer (meaning the number of items between the headSequence() and tailSequence()).

Returns:

the size

tailSequence

long tailSequence()

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

peekNextTailSequence

long peekNextTailSequence()

Returns the next sequence which the tail will be at after the next item is added. Please note that there is no item in the Ringbuffer with the returned sequence at the time of the call.

Returns:

the next sequence of the tail

setTailSequence

void setTailSequence(long tailSequence)

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

Parameters:

tailSequence - the new tail sequence

Throws:

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

See Also:

headSequence()

headSequence

long headSequence()

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

Returns:

the sequence of the head

setHeadSequence

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:

tailSequence()

isEmpty

boolean isEmpty()

Checks if the ringbuffer is empty.

Returns:

true if the ringbuffer is empty, false otherwise

add

long add(E 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

E read(long sequence)

Reads one item from the ringbuffer. This method is not destructive unlike e.g. a queue.take. So the same item can be read by multiple readers or it can be read multiple times by the same reader.

Parameters:

sequence - the sequence of the item to read

Returns:

the read item

Throws:

StaleSequenceException - if the sequence is smaller then headSequence() or larger than tailSequence(). Because a ringbuffer won't store all event indefinitely, it can be that the data for the given sequence doesn't exist anymore and the StaleSequenceException is thrown. It is up to the caller to deal with this particular situation, e.g. throw an Exception or restart from the last known head. That is why the StaleSequenceException contains the last known head.

checkBlockableReadSequence

void checkBlockableReadSequence(long readSequence)

Check if the sequence can be read from the ringbuffer or if the sequence is of the next item to be added into the ringbuffer. This method also allows the sequence to be one greater than the tailSequence(), giving the opportunity to block until the item is added into the ringbuffer.

Parameters:

readSequence - the sequence wanting to be read

Throws:

StaleSequenceException - if the requested sequence is smaller than the headSequence()

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

See Also:

headSequence(), tailSequence()

checkReadSequence

void checkReadSequence(long sequence)

Check if the sequence can be read from the ringbuffer.

Parameters:

sequence - the sequence wanting to be read

Throws:

StaleSequenceException - if the requested sequence is smaller than the headSequence()

IllegalArgumentException - if the requested sequence is greater than the tailSequence()

See Also:

headSequence(), tailSequence()

set

void set(long seq,
         E 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

void clear()

Clears the data in the ringbuffer.

getItems

E[] getItems()

Returns the array representing this ringbuffer. Items at the beginning of this array may be newer 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.