MsgHdrMemory Class — netty Architecture

Source Code

transport-classes-io_uring/src/main/java/io/netty/channel/uring/MsgHdrMemory.java lines 28–191

final class MsgHdrMemory {
    public static final int MSG_HDR_SIZE =
            Native.SIZEOF_MSGHDR + Native.SIZEOF_SOCKADDR_STORAGE + Native.SIZEOF_IOVEC + Native.CMSG_SPACE;
    private static final byte[] EMPTY_SOCKADDR_STORAGE = new byte[Native.SIZEOF_SOCKADDR_STORAGE];
    // It is not possible to have a zero length buffer in sendFd,
    // so we use a 1 byte buffer here.
    private static final int GLOBAL_IOV_LEN = 1;
    private static final ByteBuffer GLOBAL_IOV_BASE =  Buffer.allocateDirectWithNativeOrder(GLOBAL_IOV_LEN);
    private static final long GLOBAL_IOV_BASE_ADDRESS = Buffer.memoryAddress(GLOBAL_IOV_BASE);
    private final CleanableDirectBuffer msgHdrMemoryCleanable;
    private final CleanableDirectBuffer socketAddrMemoryCleanable;
    private final CleanableDirectBuffer iovMemoryCleanable;
    private final CleanableDirectBuffer cmsgDataMemoryCleanable;
    private final ByteBuffer msgHdrMemory;
    private final ByteBuffer socketAddrMemory;
    private final ByteBuffer iovMemory;
    private final ByteBuffer cmsgDataMemory;

    private final long msgHdrMemoryAddress;
    private final short idx;
    private final int cmsgDataOffset;

    MsgHdrMemory(short idx, ByteBuffer msgHdrMemoryArray) {
        this.idx = idx;
        this.msgHdrMemoryCleanable = null;
        this.socketAddrMemoryCleanable = null;
        this.iovMemoryCleanable = null;
        this.cmsgDataMemoryCleanable = null;
        int offset = idx * MSG_HDR_SIZE;
        // ByteBuffer.slice(int, int) / duplicate() are specified to produce BIG_ENDIAN byte buffers.
        // Set native order explicitly so native structs written via putInt/putLong use the expected endianness.
        this.msgHdrMemory = PlatformDependent.offsetSlice(
                msgHdrMemoryArray, offset, Native.SIZEOF_MSGHDR
        ).order(ByteOrder.nativeOrder());
        offset += Native.SIZEOF_MSGHDR;
        this.socketAddrMemory = PlatformDependent.offsetSlice(
                msgHdrMemoryArray, offset, Native.SIZEOF_SOCKADDR_STORAGE
        ).order(ByteOrder.nativeOrder());
        offset += Native.SIZEOF_SOCKADDR_STORAGE;
        this.iovMemory = PlatformDependent.offsetSlice(
                msgHdrMemoryArray, offset, Native.SIZEOF_IOVEC
        ).order(ByteOrder.nativeOrder());
        offset += Native.SIZEOF_IOVEC;
        this.cmsgDataMemory = PlatformDependent.offsetSlice(
                msgHdrMemoryArray, offset, Native.CMSG_SPACE
        ).order(ByteOrder.nativeOrder());

        msgHdrMemoryAddress = Buffer.memoryAddress(msgHdrMemory);

        long cmsgDataMemoryAddr = Buffer.memoryAddress(cmsgDataMemory);
        long cmsgDataAddr = Native.cmsghdrData(cmsgDataMemoryAddr);
        cmsgDataOffset = (int) (cmsgDataAddr - cmsgDataMemoryAddr);
    }

    MsgHdrMemory() {
        this.idx = 0;
        // jdk will memset the memory to 0, so we don't need to do it here.
        msgHdrMemoryCleanable = Buffer.allocateDirectBufferWithNativeOrder(Native.SIZEOF_MSGHDR);
        socketAddrMemoryCleanable = null;
        iovMemoryCleanable = Buffer.allocateDirectBufferWithNativeOrder(Native.SIZEOF_IOVEC);
        cmsgDataMemoryCleanable = Buffer.allocateDirectBufferWithNativeOrder(Native.CMSG_SPACE_FOR_FD);

        msgHdrMemory = msgHdrMemoryCleanable.buffer();
        socketAddrMemory = null;
        iovMemory = iovMemoryCleanable.buffer();
        cmsgDataMemory = cmsgDataMemoryCleanable.buffer();

        msgHdrMemoryAddress = Buffer.memoryAddress(msgHdrMemory);
        // These two parameters must be set to valid values and cannot be 0,
        // otherwise the fd we get in io_uring_recvmsg is 0
        Iov.set(iovMemory, GLOBAL_IOV_BASE_ADDRESS, GLOBAL_IOV_LEN);

        long cmsgDataMemoryAddr = Buffer.memoryAddress(cmsgDataMemory);
        long cmsgDataAddr = Native.cmsghdrData(cmsgDataMemoryAddr);
        cmsgDataOffset = (int) (cmsgDataAddr - cmsgDataMemoryAddr);
    }

    void set(LinuxSocket socket, InetSocketAddress address, long bufferAddress , int length, short segmentSize) {
        int addressLength;
        if (address == null) {
            addressLength = socket.isIpv6() ? Native.SIZEOF_SOCKADDR_IN6 : Native.SIZEOF_SOCKADDR_IN;