SubmissionQueue Class — netty Architecture

Source Code

transport-classes-io_uring/src/main/java/io/netty/channel/uring/SubmissionQueue.java lines 30–326

final class SubmissionQueue {
    private static final InternalLogger logger = InternalLoggerFactory.getInstance(SubmissionQueue.class);

    static final int SQE_SIZE = 64;

    //these offsets are used to access specific properties
    //SQE https://github.com/axboe/liburing/blob/liburing-2.6/src/include/liburing/io_uring.h#L30
    private static final int SQE_OP_CODE_FIELD = 0;
    private static final int SQE_FLAGS_FIELD = 1;
    private static final int SQE_IOPRIO_FIELD = 2; // u16
    private static final int SQE_FD_FIELD = 4; // s32
    private static final int SQE_UNION1_FIELD = 8;
    private static final int SQE_UNION2_FIELD = 16;
    private static final int SQE_LEN_FIELD = 24;
    private static final int SQE_UNION3_FIELD = 28;
    private static final int SQE_USER_DATA_FIELD = 32;
    private static final int SQE_UNION4_FIELD = 40;
    private static final int SQE_PERSONALITY_FIELD = 42;
    private static final int SQE_UNION5_FIELD = 44;
    private static final int SQE_UNION6_FIELD = 48;

    // These unsigned integer pointers(shared with the kernel) will be changed by the kernel and us
    // using a VarHandle.
    private static final VarHandle INT_HANDLE =
            MethodHandles.byteBufferViewVarHandle(int[].class, ByteOrder.nativeOrder());
    private final ByteBuffer kHead;
    private final ByteBuffer kTail;
    private final ByteBuffer kflags;
    private final ByteBuffer submissionQueueArray;

    final int ringEntries;
    private final int ringMask; // = ringEntries - 1

    final int ringSize;
    final long ringAddress;
    final int ringFd;
    int enterRingFd;
    private int enterFlags;
    private int head;
    private int tail;

    private boolean closed;

    SubmissionQueue(ByteBuffer khead, ByteBuffer ktail, int ringMask, int ringEntries, ByteBuffer kflags,
                    ByteBuffer submissionQueueArray,
                    int ringSize, long ringAddress,
                    int ringFd) {
        this.kHead = khead;
        this.kTail = ktail;
        this.submissionQueueArray = submissionQueueArray;
        this.ringSize = ringSize;
        this.ringAddress = ringAddress;
        this.ringFd = ringFd;
        this.enterRingFd = ringFd;
        this.ringEntries = ringEntries;
        this.kflags = kflags;
        this.ringMask = ringMask;
        this.head = (int) INT_HANDLE.getVolatile(khead, 0);
        this.tail = (int) INT_HANDLE.getVolatile(ktail, 0);
    }

    int flags() {
        if (closed) {
            return 0;
        }
        // we only need memory_order_relaxed
        return (int) INT_HANDLE.getOpaque(kflags, 0);
    }

    long submissionQueueArrayAddress() {
        return Buffer.memoryAddress(submissionQueueArray);
    }

    void close() {
        closed = true;
    }

    private void checkClosed() {
        if (closed) {
            throw new IllegalStateException();
        }