Package 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.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ByteBlockPool.Allocator	Abstract class for allocating and freeing byte blocks.
static final 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

Fields

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

Constructor Summary

Constructors

Constructor	Description
ByteBlockPool(ByteBlockPool.Allocator allocator)

Method Summary

Modifier and Type	Method	Description
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 Details

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 Details

ByteBlockPool

public ByteBlockPool(ByteBlockPool.Allocator allocator)

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:

• 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.