ObjectBuffer.java
package com.fasterxml.jackson.databind.util;
import java.lang.reflect.Array;
import java.util.List;
/**
* Helper class to use for constructing Object arrays by appending entries
* to create arrays of various lengths (length that is not known a priori).
*/
public final class ObjectBuffer
{
// // // Config constants
/**
* Also: let's expand by doubling up until 64k chunks (which is 16k entries for
* 32-bit machines)
*/
private final static int SMALL_CHUNK = (1 << 14);
/**
* Let's limit maximum size of chunks we use; helps avoid excessive allocation
* overhead for huge data sets.
* For now, let's limit to quarter million entries, 1 meg chunks for 32-bit
* machines.
*/
private final static int MAX_CHUNK = (1 << 18);
// // // Data storage
private LinkedNode<Object[]> _head;
private LinkedNode<Object[]> _tail;
/**
* Number of total buffered entries in this buffer, counting all instances
* within linked list formed by following {@link #_head}.
*/
private int _size;
// // // Simple reuse
/**
* Reusable Object array, stored here after buffer has been released having
* been used previously.
*/
private Object[] _freeBuffer;
/*
/**********************************************************
/* Construction
/**********************************************************
*/
public ObjectBuffer() { }
/*
/**********************************************************
/* Public API
/**********************************************************
*/
/**
* Method called to start buffering process. Will ensure that the buffer
* is empty, and then return an object array to start chunking content on
*/
public Object[] resetAndStart()
{
_reset();
if (_freeBuffer == null) {
return (_freeBuffer = new Object[12]);
}
return _freeBuffer;
}
/**
* @since 2.9
*/
public Object[] resetAndStart(Object[] base, int count)
{
_reset();
if ((_freeBuffer == null) || (_freeBuffer.length < count)) {
_freeBuffer = new Object[Math.max(12, count)];
}
System.arraycopy(base, 0, _freeBuffer, 0, count);
return _freeBuffer;
}
/**
* Method called to add a full Object array as a chunk buffered within
* this buffer, and to obtain a new array to fill. Caller is not to use
* the array it gives; but to use the returned array for continued
* buffering.
*
* @param fullChunk Completed chunk that the caller is requesting
* to append to this buffer. It is generally chunk that was
* returned by an earlier call to {@link #resetAndStart} or
* {@link #appendCompletedChunk} (although this is not required or
* enforced)
*
* @return New chunk buffer for caller to fill
*/
public Object[] appendCompletedChunk(Object[] fullChunk)
{
LinkedNode<Object[]> next = new LinkedNode<Object[]>(fullChunk, null);
if (_head == null) { // first chunk
_head = _tail = next;
} else { // have something already
_tail.linkNext(next);
_tail = next;
}
int len = fullChunk.length;
_size += len;
// double the size for small chunks
if (len < SMALL_CHUNK) {
len += len;
} else if (len < MAX_CHUNK) { // but by +25% for larger (to limit overhead)
len += (len >> 2);
}
return new Object[len];
}
/**
* Method called to indicate that the buffering process is now
* complete; and to construct a combined exactly-sized result
* array. Additionally the buffer itself will be reset to
* reduce memory retention.
*<p>
* Resulting array will be of generic <code>Object[]</code> type:
* if a typed array is needed, use the method with additional
* type argument.
*/
public Object[] completeAndClearBuffer(Object[] lastChunk, int lastChunkEntries)
{
int totalSize = lastChunkEntries + _size;
Object[] result = new Object[totalSize];
_copyTo(result, totalSize, lastChunk, lastChunkEntries);
_reset();
return result;
}
/**
* Type-safe alternative to
* {@link #completeAndClearBuffer(Object[], int)}, to allow
* for constructing explicitly typed result array.
*
* @param componentType Type of elements included in the buffer. Will be
* used for constructing the result array.
*/
public <T> T[] completeAndClearBuffer(Object[] lastChunk, int lastChunkEntries, Class<T> componentType)
{
int totalSize = lastChunkEntries + _size;
@SuppressWarnings("unchecked")
T[] result = (T[]) Array.newInstance(componentType, totalSize);
_copyTo(result, totalSize, lastChunk, lastChunkEntries);
_reset();
return result;
}
public void completeAndClearBuffer(Object[] lastChunk, int lastChunkEntries, List<Object> resultList)
{
for (LinkedNode<Object[]> n = _head; n != null; n = n.next()) {
Object[] curr = n.value();
for (int i = 0, len = curr.length; i < len; ++i) {
resultList.add(curr[i]);
}
}
// and then the last one
for (int i = 0; i < lastChunkEntries; ++i) {
resultList.add(lastChunk[i]);
}
_reset();
}
/**
* Helper method that can be used to check how much free capacity
* will this instance start with. Can be used to choose the best
* instance to reuse, based on size of reusable object chunk
* buffer holds reference to.
*/
public int initialCapacity() {
return (_freeBuffer == null) ? 0 : _freeBuffer.length;
}
/**
* Method that can be used to check how many Objects have been buffered
* within this buffer.
*/
public int bufferedSize() { return _size; }
/*
/**********************************************************
/* Internal methods
/**********************************************************
*/
protected void _reset()
{
// can we reuse the last (and thereby biggest) array for next time?
if (_tail != null) {
_freeBuffer = _tail.value();
}
// either way, must discard current contents
_head = _tail = null;
_size = 0;
}
protected final void _copyTo(Object resultArray, int totalSize,
Object[] lastChunk, int lastChunkEntries)
{
int ptr = 0;
for (LinkedNode<Object[]> n = _head; n != null; n = n.next()) {
Object[] curr = n.value();
int len = curr.length;
System.arraycopy(curr, 0, resultArray, ptr, len);
ptr += len;
}
System.arraycopy(lastChunk, 0, resultArray, ptr, lastChunkEntries);
ptr += lastChunkEntries;
// sanity check (could have failed earlier due to out-of-bounds, too)
if (ptr != totalSize) {
throw new IllegalStateException("Should have gotten "+totalSize+" entries, got "+ptr);
}
}
}