net.openhft.chronicle.queue

Interface ChronicleQueue

All Superinterfaces:

AutoCloseable, Closeable

All Known Implementing Classes:

AbstractChronicle, AbstractChronicleQueue, IndexedSingleChronicleQueue

public interface ChronicleQueue
extends Closeable

Chronicle (in a generic sense) is a Java project focused on building a persisted low latency messaging framework for high performance and critical applications.

Using non-heap storage options Chronicle provides a processing environment where applications does not suffer from GarbageCollection. GarbageCollection (GC) may slow down your critical operations non-deterministically at any time.. In order to avoid non-determinism and escape from GC delays off-heap memory solutions are addressed. The main idea is to manage your memory manually so does not suffer from GC. Chronicle behaves like a management interface over off-heap memory so you can build your own solutions over it.

Chronicle uses RandomAccessFiles while managing memory and this choice brings lots of possibility. Random access files permit non-sequential, or random, access to a file's contents. To access a file randomly, you open the file, seek a particular location, and read from or write to that file. RandomAccessFiles can be seen as "large" C-type byte arrays that you can access any random index "directly" using pointers. File portions can be used as ByteBuffers if the portion is mapped into memory.

ChronicleQueue (now in the specific sense) is the main interface for management and can be seen as the "Collection class" of the Chronicle environment. You will reserve a portion of memory and then put/fetch/update records using the ChronicleQueue interface.

Excerpt is the main data container in a ChronicleQueue, each Chronicle is composed of Excerpts. Putting data to a queue means starting a new Excerpt, writing data into it and finishing the Excerpt at the upper.

While Excerpt is a generic purpose container allowing for remote access, it also has more specialized counterparts for sequential operations. See ExcerptTailer and ExcerptAppender

Author:

peter.lawrey

Method Summary

Modifier and Type	Method and Description
void	clear() Remove all the entries in the queue.
ExcerptAppender	createAppender() An Appender can be used to write new excerpts sequentially to the upper.
Excerpt	createExcerpt() An Excerpt can be used access entries randomly and optionally change them.
ExcerptTailer	createTailer() A Tailer can be used to read sequentially from the lower of a given position.
long	firstAvailableIndex()
long	lastWrittenIndex()
String	name()
long	size()

Methods inherited from interface java.io.Closeable

close

Method Detail

name

String name()

Returns:

A descriptive name for this queue which can be used for logging.

createExcerpt

@NotNull
Excerpt createExcerpt()
                        throws IOException

An Excerpt can be used access entries randomly and optionally change them.

Returns:

Excerpt

Throws:

IOException - if an IO problem occurs

createTailer

@NotNull
ExcerptTailer createTailer()
                             throws IOException

A Tailer can be used to read sequentially from the lower of a given position.

Returns:

ExcerptTailer

Throws:

IOException - if an IO problem occurs

createAppender

@NotNull
ExcerptAppender createAppender()
                                 throws IOException

An Appender can be used to write new excerpts sequentially to the upper.

Returns:

ExcerptAppender

Throws:

IOException - if an IO problem occurs

size

long size()

Returns:

The current estimated number of entries.

clear

void clear()

Remove all the entries in the queue.

firstAvailableIndex

long firstAvailableIndex()

Returns:

the lowest valid index available.

lastWrittenIndex

long lastWrittenIndex()

Returns:

the highest valid index immediately available.