com.fasterxml.jackson.databind.util.ObjectBuffer Maven / Gradle / Ivy

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 _head;

    private LinkedNode _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 next = new LinkedNode(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.
     *
     * Resulting array will be of generic Object[] 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[] completeAndClearBuffer(Object[] lastChunk, int lastChunkEntries, Class 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