PoolSubpage Class — netty Architecture

Source Code

buffer/src/main/java/io/netty/buffer/PoolSubpage.java lines 26–300

final class PoolSubpage<T> implements PoolSubpageMetric {

    final PoolChunk<T> chunk;
    final int elemSize;
    private final int pageShifts;
    private final int runOffset;
    private final int runSize;
    private final long[] bitmap;
    private final int bitmapLength;
    private final int maxNumElems;
    final int headIndex;

    PoolSubpage<T> prev;
    PoolSubpage<T> next;

    boolean doNotDestroy;
    private int nextAvail;
    private int numAvail;

    final ReentrantLock lock;

    // TODO: Test if adding padding helps under contention
    //private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;

    /** Special constructor that creates a linked list head */
    PoolSubpage(int headIndex) {
        chunk = null;
        lock = new ReentrantLock();
        pageShifts = -1;
        runOffset = -1;
        elemSize = -1;
        runSize = -1;
        bitmap = null;
        bitmapLength = -1;
        maxNumElems = 0;
        this.headIndex = headIndex;
    }

    PoolSubpage(PoolSubpage<T> head, PoolChunk<T> chunk, int pageShifts, int runOffset, int runSize, int elemSize) {
        this.headIndex = head.headIndex;
        this.chunk = chunk;
        this.pageShifts = pageShifts;
        this.runOffset = runOffset;
        this.runSize = runSize;
        this.elemSize = elemSize;

        doNotDestroy = true;

        maxNumElems = numAvail = runSize / elemSize;
        int bitmapLength = maxNumElems >>> 6;
        if ((maxNumElems & 63) != 0) {
            bitmapLength ++;
        }
        this.bitmapLength = bitmapLength;
        bitmap = new long[bitmapLength];
        nextAvail = 0;

        lock = null;
        addToPool(head);
    }

    /**
     * Returns the bitmap index of the subpage allocation.
     */
    long allocate() {
        if (numAvail == 0 || !doNotDestroy) {
            return -1;
        }

        final int bitmapIdx = getNextAvail();
        if (bitmapIdx < 0) {
            removeFromPool(); // Subpage appear to be in an invalid state. Remove to prevent repeated errors.
            throw new AssertionError("No next available bitmap index found (bitmapIdx = " + bitmapIdx + "), " +
                    "even though there are supposed to be (numAvail = " + numAvail + ") " +
                    "out of (maxNumElems = " + maxNumElems + ") available indexes.");
        }
        int q = bitmapIdx >>> 6;
        int r = bitmapIdx & 63;
        assert (bitmap[q] >>> r & 1) == 0;
        bitmap[q] |= 1L << r;