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## org.apache.lucene.util
Class ByteBlockPool

    java.lang.Object
      org.apache.lucene.util.ByteBlockPool

    public final class ByteBlockPool

extends Object

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.

Nested Class Summary
`static class` | `ByteBlockPool.Allocator` Abstract class for allocating and freeing byte blocks.
`static class` | `ByteBlockPool.DirectAllocator` A simple `ByteBlockPool.Allocator` that never recycles.
`static class` | `ByteBlockPool.DirectTrackingAllocator` A simple `ByteBlockPool.Allocator` that never recycles, but tracks how much total RAM is in use.

Field Summary
`byte[]` | `buffer` Current head buffer
`byte[][]` | `buffers` array of buffers currently used in the pool.
`static int` | `BYTE_BLOCK_MASK`
`static int` | `BYTE_BLOCK_SHIFT`
`static int` | `BYTE_BLOCK_SIZE`
`int` | `byteOffset` Current head offset
`int` | `byteUpto` Where we are in head buffer
`static int` | `FIRST_LEVEL_SIZE` The first level size for new slices
`static int[]` | `LEVEL_SIZE_ARRAY` An array holding the level sizes for byte slices.
`static int[]` | `NEXT_LEVEL_ARRAY` An array holding the offset into the `LEVEL_SIZE_ARRAY` to quickly navigate to the next slice level.

Constructor Summary
`ByteBlockPool(ByteBlockPool.Allocator allocator)`

Method Summary
`int` | `allocSlice(byte[] slice, int upto)` Creates a new byte slice with the given starting size and returns the slices offset in the pool.
`void` | `append(BytesRef bytes)` Appends the bytes in the provided `BytesRef` at the current position.
`int` | `newSlice(int size)` Allocates a new slice with the given size.
`void` | `nextBuffer()` Advances the pool to its next buffer.
`void` | `readBytes(long offset, byte[] bytes, int off, int length)` Reads bytes bytes out of the pool starting at the given offset with the given length into the given byte array at offset `off`.
`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)`.
`void` | `reset(boolean zeroFillBuffers, boolean reuseFirst)` Expert: Resets the pool to its initial state reusing the first buffer.
`void` | `setBytesRef(BytesRef term, int textStart)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### BYTE_BLOCK_SHIFT

    public static final int BYTE_BLOCK_SHIFT

See Also:
  Constant Field Values

### BYTE_BLOCK_SIZE

    public static final int BYTE_BLOCK_SIZE

See Also:
  Constant Field Values

### BYTE_BLOCK_MASK

    public static final int BYTE_BLOCK_MASK

See Also:
  Constant Field Values

### 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:
    `newSlice(int)`

Constructor Detail

### ByteBlockPool

    public ByteBlockPool(ByteBlockPool.Allocator allocator)

Method Detail

### 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:
    `FIRST_LEVEL_SIZE`

### 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 off,
                          int length)

  Reads bytes 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.

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