org.archive.queue
Class DiskQueue

java.lang.Object
  org.archive.queue.DiskQueue

All Implemented Interfaces:

java.io.Serializable, Queue

public class DiskQueue
extends java.lang.Object
implements Queue, java.io.Serializable

Queue which stores all its objects to disk using object serialization, on top of a DiskBackedByteQueue. The serialization state is reset after each enqueue(). Care should be taken not to enqueue() items which will pull out excessive referenced objects, or objects which will be redundantly reinstantiated upon dequeue() from disk. This class is not synchronized internally.

Author:

Gordon Mohr

See Also:

Serialized Form

Field Summary

(package private) DiskByteQueue	bytes The object which shuffles raw bytes to/from disk.
(package private) java.lang.Object	headObject top item in queue, pulled into memory for peek()
(package private) java.io.ObjectInputStream	headStream
(package private) long	length the number of elements currently in the queue
(package private) java.lang.String	prefix the prefix for the files created in the scratchDir
(package private) java.io.ObjectOutputStream	tailStream

Constructor Summary

DiskQueue(java.io.File file, java.lang.String file_prefix)
Create a new DiskQueue which creates its temporary files in a given directory, with a given prefix.

DiskQueue(java.io.File dir, java.lang.String prefix, boolean reuse)
Create a new DiskQueue which creates its temporary files in a given directory, with a given prefix, and reuse any prexisting backing files as directed.

Method Summary

void	connect() Reconnect to disk-based backing
long	deleteMatchedItems(org.apache.commons.collections.Predicate matcher) All objects in the queue where matcher.match(object) returns true will be deleted from the queue.
java.lang.Object	dequeue() remove an entry from the start of the queue
void	disconnect() Disconnect from any backing files, without deleting those files, allowing reattachment later.
void	enqueue(java.lang.Object o) Add an entry to the end of queue
java.util.Iterator	getIterator(boolean inCacheOnly) Returns an iterator for the queue.
boolean	isEmpty() is the queue empty?
protected boolean	isInitialized()
long	length() get the number of elements in the queue
java.lang.Object	peek() Give the top object in the queue, leaving it in place to be returned by future peek() or dequeue() invocations.
void	release() release any OS/IO resources associated with Queue
void	unpeek() Releases queue from the obligation to return in the next peek()/dequeue() the same object as returned by any previous peek().

Methods inherited from class java.lang.Object

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

Field Detail

length

long length

the number of elements currently in the queue

headObject

java.lang.Object headObject

top item in queue, pulled into memory for peek()

prefix

java.lang.String prefix

the prefix for the files created in the scratchDir

bytes

DiskByteQueue bytes

The object which shuffles raw bytes to/from disk.

tailStream

transient java.io.ObjectOutputStream tailStream

headStream

transient java.io.ObjectInputStream headStream

Constructor Detail

DiskQueue

public DiskQueue(java.io.File dir,
                 java.lang.String prefix,
                 boolean reuse)
          throws java.io.IOException

Create a new DiskQueue which creates its temporary files in a given directory, with a given prefix, and reuse any prexisting backing files as directed.

Parameters:

dir - the directory in which to create the data files

prefix -

reuse - whether to reuse any existing backing files

Throws:

java.io.IOException - if we cannot create an appropriate file

DiskQueue

public DiskQueue(java.io.File file,
                 java.lang.String file_prefix)
          throws java.io.IOException

Create a new DiskQueue which creates its temporary files in a given directory, with a given prefix.

Parameters:

file -

file_prefix -

Throws:

java.io.IOException

Method Detail

isInitialized

protected boolean isInitialized()

enqueue

public void enqueue(java.lang.Object o)

Description copied from interface: Queue

Add an entry to the end of queue

Specified by:

enqueue in interface Queue

Parameters:

o - the entry to queue

See Also:

Queue.enqueue(java.lang.Object)

isEmpty

public boolean isEmpty()

Description copied from interface: Queue

is the queue empty?

Specified by:

isEmpty in interface Queue

Returns:

true if the queue has no elements

See Also:

Queue.isEmpty()

dequeue

public java.lang.Object dequeue()

Description copied from interface: Queue

remove an entry from the start of the queue

Specified by:

dequeue in interface Queue

Returns:

the object

See Also:

Queue.dequeue()

peek

public java.lang.Object peek()

Description copied from interface: Queue

Give the top object in the queue, leaving it in place to be returned by future peek() or dequeue() invocations.

Specified by:

peek in interface Queue

Returns:

top object, without removing it

See Also:

Queue.peek()

unpeek

public void unpeek()

Description copied from interface: Queue

Releases queue from the obligation to return in the next peek()/dequeue() the same object as returned by any previous peek().

Specified by:

unpeek in interface Queue

length

public long length()

Description copied from interface: Queue

get the number of elements in the queue

Specified by:

length in interface Queue

Returns:

the number of elements in the queue

See Also:

Queue.length()

release

public void release()

Description copied from interface: Queue

release any OS/IO resources associated with Queue

Specified by:

release in interface Queue

See Also:

Queue.release()

disconnect

public void disconnect()

Disconnect from any backing files, without deleting those files, allowing reattachment later.

connect

public void connect()

Reconnect to disk-based backing

getIterator

public java.util.Iterator getIterator(boolean inCacheOnly)

Description copied from interface: Queue

Returns an iterator for the queue.

The returned iterator's remove method is considered unsafe.

Editing the queue while using the iterator is not safe.

Specified by:

getIterator in interface Queue

Returns:

iterator

See Also:

Queue.getIterator(boolean)

deleteMatchedItems

public long deleteMatchedItems(org.apache.commons.collections.Predicate matcher)

Description copied from interface: Queue

All objects in the queue where matcher.match(object) returns true will be deleted from the queue.

Making other changes to the queue while this method is being processed is not safe.

Specified by:

deleteMatchedItems in interface Queue

Parameters:

matcher - a predicate

Returns:

the number of deleted items

See Also:

Queue.deleteMatchedItems(org.apache.commons.collections.Predicate)