Class ByteBlockPool

java.lang.Object
org.apache.lucene.util.ByteBlockPool
All Implemented Interfaces:
Accountable

public final class ByteBlockPool extends Object implements Accountable
Class that Posting and PostingVector use to write byte streams into shared fixed-size byte[] arrays. The idea is to allocate slices of increasing lengths For example, the first slice is 5 bytes, the next slice is 14, etc. We start by writing our bytes into the first 5 bytes. When we hit the end of the slice, we allocate the next slice and then write the address of the new slice into the last 4 bytes of the previous slice (the "forwarding address").

Each slice is filled with 0's initially, and we mark the end with a non-zero byte. This way the methods that are writing into the slice don't need to record its length and instead allocate a new slice once they hit a non-zero byte.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.
  • Field Details

    • BYTE_BLOCK_SHIFT

      public static final int BYTE_BLOCK_SHIFT
      See Also:
    • BYTE_BLOCK_SIZE

      public static final int BYTE_BLOCK_SIZE
      See Also:
    • BYTE_BLOCK_MASK

      public static final int BYTE_BLOCK_MASK
      See Also:
    • buffers

      public byte[][] buffers
      array of buffers currently used in the pool. Buffers are allocated if needed don't modify this outside of this class.
    • byteUpto

      public int byteUpto
      Where we are in head buffer
    • buffer

      public byte[] buffer
      Current head buffer
    • byteOffset

      public int byteOffset
      Current head offset
    • NEXT_LEVEL_ARRAY

      public static final int[] NEXT_LEVEL_ARRAY
      An array holding the offset into the LEVEL_SIZE_ARRAY to quickly navigate to the next slice level.
    • LEVEL_SIZE_ARRAY

      public static final int[] LEVEL_SIZE_ARRAY
      An array holding the level sizes for byte slices.
    • FIRST_LEVEL_SIZE

      public static final int FIRST_LEVEL_SIZE
      The first level size for new slices
      See Also:
  • Constructor Details

  • Method Details

    • reset

      public void reset()
      Resets the pool to its initial state reusing the first buffer and fills all buffers with 0 bytes before they reused or passed to ByteBlockPool.Allocator.recycleByteBlocks(byte[][], int, int). Calling nextBuffer() is not needed after reset.
    • reset

      public void reset(boolean zeroFillBuffers, boolean reuseFirst)
      Expert: Resets the pool to its initial state reusing the first buffer. Calling nextBuffer() is not needed after reset.
      Parameters:
      zeroFillBuffers - if true the buffers are filled with 0. This should be set to true if this pool is used with slices.
      reuseFirst - if true the first buffer will be reused and calling nextBuffer() is not needed after reset iff the block pool was used before ie. nextBuffer() was called before.
    • nextBuffer

      public void nextBuffer()
      Advances the pool to its next buffer. This method should be called once after the constructor to initialize the pool. In contrast to the constructor a reset() call will advance the pool to its first buffer immediately.
    • newSlice

      public int newSlice(int size)
      Allocates a new slice with the given size.
      See Also:
    • allocSlice

      public int allocSlice(byte[] slice, int upto)
      Creates a new byte slice with the given starting size and returns the slices offset in the pool.
    • setBytesRef

      public void setBytesRef(BytesRef term, int textStart)
    • append

      public void append(BytesRef bytes)
      Appends the bytes in the provided BytesRef at the current position.
    • readBytes

      public void readBytes(long offset, byte[] bytes, int bytesOffset, int bytesLength)
      Reads bytes out of the pool starting at the given offset with the given length into the given byte array at offset off.

      Note: this method allows to copy across block boundaries.

    • setRawBytesRef

      public void setRawBytesRef(BytesRef ref, long offset)
      Set the given BytesRef so that its content is equal to the ref.length bytes starting at offset. Most of the time this method will set pointers to internal data-structures. However, in case a value crosses a boundary, a fresh copy will be returned. On the contrary to setBytesRef(BytesRef, int), this does not expect the length to be encoded with the data.
    • ramBytesUsed

      public long ramBytesUsed()
      Description copied from interface: Accountable
      Return the memory usage of this object in bytes. Negative values are illegal.
      Specified by:
      ramBytesUsed in interface Accountable