net.openhft.chronicle.queue

Interface ExcerptTailer

All Superinterfaces:

ExcerptCommon<ExcerptTailer>, net.openhft.chronicle.wire.MarshallableIn, net.openhft.chronicle.wire.SourceContext

All Known Implementing Classes:

SingleChronicleQueueExcerpts.StoreTailer

public interface ExcerptTailer
extends ExcerptCommon<ExcerptTailer>, net.openhft.chronicle.wire.MarshallableIn, net.openhft.chronicle.wire.SourceContext

The component that facilitates sequentially reading data from a ChronicleQueue.

NOTE: Tailers are NOT thread-safe, sharing the Tailer between threads will lead to errors and unpredictable behaviour.

Author:

peter.lawrey

Method Summary

Modifier and Type	Method and Description
ExcerptTailer	afterLastWritten(ChronicleQueue queue) Wind this tailer to after the last entry which wrote an entry to the queue
int	cycle()
TailerDirection	direction()
ExcerptTailer	direction(TailerDirection direction) Set the direction of movement.
default Runnable	getCloserJob() A task that will be run if a WeakReference referring this appender is registered with a clean-up task.
long	index()
ExcerptTailer	indexing(boolean indexing) Causes this tailer to update the index as queue excerpts are read
boolean	moveToIndex(long index) Randomly select an Excerpt.
default boolean	readAfterReplicaAcknowledged()
default void	readAfterReplicaAcknowledged(boolean readAfterReplicaAcknowledged)
default net.openhft.chronicle.wire.DocumentContext	readingDocument() equivalent to MarshallableIn.readDocument(ReadMarshallable) but with out the use of a lambda expression.
net.openhft.chronicle.wire.DocumentContext	readingDocument(boolean includeMetaData)
TailerState	state()
ExcerptTailer	toEnd() Wind to the last entry in the last cycle
ExcerptTailer	toStart() Replay from the first entry in the first cycle.

Methods inherited from interface net.openhft.chronicle.queue.ExcerptCommon

queue, sourceId

Methods inherited from interface net.openhft.chronicle.wire.MarshallableIn

methodReader, methodReaderBuilder, readBytes, readBytes, readDocument, readMap, readText, readText

Methods inherited from interface net.openhft.chronicle.wire.SourceContext

sourceId

Method Detail

readingDocument

@NotNull
default net.openhft.chronicle.wire.DocumentContext readingDocument()

equivalent to MarshallableIn.readDocument(ReadMarshallable) but with out the use of a lambda expression.

This method is the ExcerptTailer equivalent of WireIn.readingDocument()

Specified by:

readingDocument in interface net.openhft.chronicle.wire.MarshallableIn

Returns:

the document context

readingDocument

@NotNull
net.openhft.chronicle.wire.DocumentContext readingDocument(boolean includeMetaData)

index

long index()

Specified by:

index in interface net.openhft.chronicle.wire.SourceContext

Returns:

if called while within the try (tailer.readingDocument){ } block, returns index of current reading document. Otherwise, the next index to read. Index includes the cycle and the sequence number in that cycle

cycle

int cycle()

Returns:

the cycle this appender is on, usually with chronicle-queue each cycle will have its own unique data file to store the excerpt

moveToIndex

boolean moveToIndex(long index)

Randomly select an Excerpt.

Parameters:

index - index to look up, the index includes the cycle number and a sequence number from with this cycle

Returns:

true if this is a valid entries.

toStart

@NotNull
ExcerptTailer toStart()

Replay from the first entry in the first cycle.

Returns:

this Excerpt

toEnd

@NotNull
ExcerptTailer toEnd()

Wind to the last entry in the last cycle

If the direction() == FORWARD, this will be 1 more than the last entry.
Otherwise the index will be the last entry.

This is not atomic with the appenders, in other words if a cycle has been added in the current millisecond, toEnd() may not see it, This is because for performance reasons, the queue.lastCycle() is cached, as finding the last cycle is expensive, it requires asking the directory for the Files.list() so, this cache is only refreshed if the call toEnd() is in a new millisecond. Hence a whole milliseconds with of data could be added to the chronicle-queue that toEnd() won’t see. For appenders that that are on the same JVM, they can be informed that the last cycle has changed, this will yield better results, but atomicity can still not be guaranteed.

Returns:

this Excerpt

direction

TailerDirection direction()

Returns:

the direction of movement after reading an entry.

direction

@NotNull
ExcerptTailer direction(TailerDirection direction)

Set the direction of movement.

Parameters:

direction - NONE, FORWARD, BACKWARD

Returns:

this

afterLastWritten

@NotNull
ExcerptTailer afterLastWritten(ChronicleQueue queue)
                                 throws net.openhft.chronicle.core.io.IORuntimeException

Wind this tailer to after the last entry which wrote an entry to the queue

Parameters:

queue - which was written to.

Returns:

this ExcerptTailer

Throws:

net.openhft.chronicle.core.io.IORuntimeException - if the queue couldn't be wound to the last index.

indexing

@NotNull
ExcerptTailer indexing(boolean indexing)

Causes this tailer to update the index as queue excerpts are read

Parameters:

indexing - should this ExcerptTailer perform indexing

Returns:

this ExcerptTailer

readAfterReplicaAcknowledged

default void readAfterReplicaAcknowledged(boolean readAfterReplicaAcknowledged)

readAfterReplicaAcknowledged

default boolean readAfterReplicaAcknowledged()

state

@NotNull
TailerState state()

getCloserJob

default Runnable getCloserJob()

A task that will be run if a WeakReference referring this appender is registered with a clean-up task.

Returns:

Task to release any associated resources