it.unimi.dsi.io

Class ByteDiskQueue

java.lang.Object

it.unimi.dsi.io.ByteDiskQueue

All Implemented Interfaces:

Size64, Closeable, AutoCloseable

public class ByteDiskQueue
extends Object
implements Closeable, Size64

A queue of bytes partially stored on disk.

Instances of this class keep track of a queue of bytes using a circular (and possibly direct) ByteBuffer that contains the head and the tail of the queue. The central part of the queue, if necessary, is dumped on disk. Note that clear() does empty the queue, but it does not remove the dump file on disk: use trim() to trim the file at the smallest possible length. The dump file can be removed only with a call to close(), or when the instance is finalised.

Since file handles are a precious resource, this class provides a suspend() method that releases the file handle without deleting the dump file. All calls to methods accessing the file handle will reinitialise it lazily (which implies that a certain number of enqueues/dequeues can be performed on a suspended class without actually reopening the dump file).

You can create a queue using a new or empty file, or using an existing file, in which case the content of the file will become the content of the queue. A freeze() method closes a queue but leaves behind a dump file containing the current content of the queue, so that it can be reopened later.

Warning: the close() method will delete the queue file from disk. This implies that if a file with the same name has been created in the meanwhile, it will be deleted.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ByteDiskQueue(File file, int bufferSize, boolean direct, boolean useFileContent) Creates a new disk-based byte queue.

Method Summary

Methods

Modifier and Type	Method and Description
void	clear() Clears the queue.
void	close() Deallocates all disk resources associated with this queue.
static ByteDiskQueue	createFromFile(File file, int bufferSize, boolean direct) Creates a new disk-based byte queue using the content of an existing file.
static ByteDiskQueue	createNew(File file, int bufferSize, boolean direct) Creates a new empty disk-based byte queue.
byte	dequeue() Dequeues a byte from the queue.
void	dequeue(byte[] a) Dequeues a sequence of bytes from this queue into an array.
void	dequeue(byte[] a, int offset, int length) Dequeues a sequence of bytes from this queue into an array.
int	dequeueInt() Dequeues from this queue a vByte-coded natural number.
void	enlargeBuffer(int newBufferSize) Enlarge the size of the buffer of this queue to a given size.
void	enqueue(byte b) Enqueues a byte to this queue.
void	enqueue(byte[] a) Enqueues a byte array to this queue.
void	enqueue(byte[] a, int offset, int length) Enqueues a fragment of byte array to this queue.
void	enqueueInt(int x) Adds a vByte-coded natural number to this queue.
protected void	finalize()
void	freeze()
boolean	isEmpty()
int	size() Deprecated.
long	size64()
void	suspend() Suspends this queue, releasing the associated file handles.
void	trim() Trims the queue dump file at the current write position.

Methods inherited from class java.lang.Object

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

Constructor Detail

ByteDiskQueue

protected ByteDiskQueue(File file,
             int bufferSize,
             boolean direct,
             boolean useFileContent)
                 throws IOException

Creates a new disk-based byte queue.

Parameters:

file - the file that will be used to dump the central part of the queue on disk.

bufferSize - the capacity of the circular buffer (will be possibly decreased so to be a power of two).

direct - whether the circular ByteBuffer used by this queue should be allocated directly.

useFileContent - whether the queue is new or should use the content of an existing file; in the first case, we check that the file does not exists or has length zero.

Throws:

IOException

Method Detail

createNew

public static ByteDiskQueue createNew(File file,
                      int bufferSize,
                      boolean direct)
                               throws IOException

Creates a new empty disk-based byte queue.

Parameters:

file - the file that will be used to dump the central part of the queue on disk (must not exist or have length zero).

bufferSize - the capacity of the circular buffer (will be possibly decreased so to be a power of two).

direct - whether the circular ByteBuffer used by this queue should be allocated directly.

Throws:

IOException

createFromFile

public static ByteDiskQueue createFromFile(File file,
                           int bufferSize,
                           boolean direct)
                                    throws IOException

Creates a new disk-based byte queue using the content of an existing file. The stream of bytes contained in the provided file will form the initial content of the queue.

Parameters:

file - the file that will be used to dump the central part of the queue on disk (must exist).

bufferSize - the capacity of the circular buffer (will be possibly decreased so to be a power of two).

direct - whether the circular ByteBuffer used by this queue should be allocated directly.

Throws:

IOException

enqueue

public void enqueue(byte b)
             throws IOException

Enqueues a byte to this queue.

Parameters:

b - the byte to be enqueued.

Throws:

IOException

enqueueInt

public void enqueueInt(int x)
                throws IOException

Adds a vByte-coded natural number to this queue.

Parameters:

x - the natural number to be added to the queue.

Throws:

IOException

enqueue

public void enqueue(byte[] a,
           int offset,
           int length)
             throws IOException

Enqueues a fragment of byte array to this queue.

Parameters:

a - a byte array.

offset - the first byte in a to be enqueued.

length - the number of bytes to enqueue.

Throws:

IOException

enqueue

public void enqueue(byte[] a)
             throws IOException

Enqueues a byte array to this queue.

Parameters:

a - the array whose bytes have to be enqueued.

Throws:

IOException

dequeue

public byte dequeue()
             throws IOException

Dequeues a byte from the queue.

Returns:

the first available byte in this queue.

Throws:

NoSuchElementException - if there are no bytes in this queue.

IOException

dequeue

public void dequeue(byte[] a,
           int offset,
           int length)
             throws IOException

Dequeues a sequence of bytes from this queue into an array.

Parameters:

a - a byte array.

offset - the first position in a where dequeued bytes will be written.

length - the number of bytes to dequeue.

Throws:

NoSuchElementException - if there are not enough bytes in this queue.

IOException

dequeue

public void dequeue(byte[] a)
             throws IOException

Dequeues a sequence of bytes from this queue into an array.

Parameters:

a - the array that will contain the dequeued bytes.

Throws:

NoSuchElementException - if there are not enough bytes in this queue.

IOException

dequeueInt

public int dequeueInt()
               throws IOException

Dequeues from this queue a vByte-coded natural number.

Returns:

the first available natural number in this queue.

Throws:

IOException

size

@Deprecated
public int size()

Deprecated.

Specified by:

size in interface Size64

size64

public long size64()

Specified by:

size64 in interface Size64

isEmpty

public boolean isEmpty()

close

public void close()
           throws IOException

Deallocates all disk resources associated with this queue. After calling this method, calls to any methods that would modify the queue will cause an IllegalStateException.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException

freeze

public void freeze()
            throws IOException

Throws:

IOException

clear

public void clear()

Clears the queue. Note that we do not modify the dump file (use trim() to that purpose).

trim

public void trim()
          throws IOException

Trims the queue dump file at the current write position.

Throws:

IOException

suspend

public void suspend()
             throws IOException

Suspends this queue, releasing the associated file handles. If the deque is already suspended, does nothing. The queue will lazily resume its operations when necessary.

Throws:

IOException

finalize

protected void finalize()
                 throws Throwable

Overrides:

finalize in class Object

Throws:

Throwable

enlargeBuffer

public void enlargeBuffer(int newBufferSize)

Enlarge the size of the buffer of this queue to a given size.

Parameters:

newBufferSize - the required buffer size (will be possibly decreased so to be a power of two). If the new buffer size is smaller than the current size, nothing happens.