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

  • Method Summary

    Modifier and Type
    Method
    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 Details

    • 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 Details

    • 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 AutoCloseable
      Specified by:
      close in interface Closeable
      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.