Package org.dspace.ctask.replicate

Class FilteredFileTaskQueue

java.lang.Object

org.dspace.curate.FileTaskQueue

org.dspace.ctask.replicate.FilteredFileTaskQueue

All Implemented Interfaces:

org.dspace.curate.TaskQueue

public class FilteredFileTaskQueue
extends org.dspace.curate.FileTaskQueue

An extension of the default FileTaskQueue which ensures that duplicate entries in the queue are filtered out during the "dequeue()" process.

In other words, if multiple entries in the queue include the exact same task listing and the exact same object, only the first entry will be processed.

For example, assuming a FileTaskQueue with the following contents:
user1@myu.edu|123456789|transmitaip|10673/0
user1@myu.edu|123456790|transmitaip|10673/1
user2@myu.edu|123456791|transmitaip|10673/0
user1@myu.edu|123456792|transmitaip|10673/0
Only the first TWO entries will be returned by "dequeue()", as entries #3 and #4 would be considered duplicates of entry #1.

This FilteredFileTaskQueue is extremely useful to Replication Tasks, as it ensures that AIPs are not (re-)generated multiple times when the queue is actually processed. (NOTE however that some of the Replication store plugins avoid duplicate transfers by ensuring Checksums differ before transferring)

Author:

Tim Donohue

Field Summary

Fields inherited from class org.dspace.curate.FileTaskQueue

readList, readTicket, tqDir

Constructor Summary

Constructors

Constructor	Description
FilteredFileTaskQueue()

Method Summary

Modifier and Type	Method	Description
Set<org.dspace.curate.TaskQueueEntry>	dequeue(String queueName, long ticket)	Returns the set of UNIQUE task entries from the named queue.

Methods inherited from class org.dspace.curate.FileTaskQueue

enqueue, enqueue, ensureQueue, queueNames, release

Methods inherited from class java.lang.Object

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

Constructor Detail

FilteredFileTaskQueue

public FilteredFileTaskQueue()

Method Detail

dequeue

public Set<org.dspace.curate.TaskQueueEntry> dequeue(String queueName,
                                                     long ticket)
                                              throws IOException

Returns the set of UNIQUE task entries from the named queue. Any duplicate task entries in the queue are ignored. The operation locks the queue from any further enqueue or dequeue operations until a release is called. The ticket may be any number, but a timestamp should guarantee sufficient uniqueness.

Specified by:

dequeue in interface org.dspace.curate.TaskQueue

Overrides:

dequeue in class org.dspace.curate.FileTaskQueue

Parameters:

queueName - the name of the queue to read

ticket - a token which must be presented to release the queue

Returns:

set the current set of queued unique task entries

Throws:

IOException - if I/O error