The server gets the read event, and the network module starts to read the message

public final class NioEventLoop extends SingleThreadEventLoop
// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead
// to a spin loop
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
    unsafe.read();
}

 

Obtain network channel configuration, judge whether to read automatically and prepare to read flag bit

public abstract class AbstractNioByteChannel extends AbstractNioChannel
protected class NioByteUnsafe extends AbstractNioUnsafe
public final void read() {
    final ChannelConfig config = config();
    if (!config.isAutoRead() && !isReadPending()) {
        // ChannelConfig.setAutoRead(false) was called in the meantime
        removeReadOp();
        return;
    }

    final ChannelPipeline pipeline = pipeline();
    final ByteBufAllocator allocator = config.getAllocator();
    final int maxMessagesPerRead = config.getMaxMessagesPerRead();
    RecvByteBufAllocator.Handle allocHandle = this.allocHandle;
    if (allocHandle == null) {
        this.allocHandle = allocHandle = config.getRecvByteBufAllocator().newHandle();
    }
}

Get the memory allocator. The parameters are true, false and true by default.

final ByteBufAllocator allocator = config.getAllocator();

public UnpooledByteBufAllocator(boolean preferDirect, boolean disableLeakDetector, boolean tryNoCleaner) {
    super(preferDirect);
    this.disableLeakDetector = disableLeakDetector;
    noCleaner = tryNoCleaner && PlatformDependent.hasUnsafe()
            && PlatformDependent.hasDirectBufferNoCleanerConstructor();
}

protected AbstractByteBufAllocator(boolean preferDirect) {
    directByDefault = preferDirect && PlatformDependent.hasUnsafe();
    emptyBuf = new EmptyByteBuf(this);
}

Get receive memory allocation processor

static final int DEFAULT_MINIMUM = 64;
static final int DEFAULT_INITIAL = 1024;
static final int DEFAULT_MAXIMUM = 65536;
private AdaptiveRecvByteBufAllocator() {
    this(DEFAULT_MINIMUM, DEFAULT_INITIAL, DEFAULT_MAXIMUM);
}

The memory size value of each level is initialized by default

static {
    List<Integer> sizeTable = new ArrayList<Integer>();
    for (int i = 16; i < 512; i += 16) {
        sizeTable.add(i);
    }

    for (int i = 512; i > 0; i <<= 1) {
        sizeTable.add(i);
    }

    SIZE_TABLE = new int[sizeTable.size()];
    for (int i = 0; i < SIZE_TABLE.length; i ++) {
        SIZE_TABLE[i] = sizeTable.get(i);
    }
}

public AdaptiveRecvByteBufAllocator(int minimum, int initial, int maximum) {
    if (minimum <= 0) {
        throw new IllegalArgumentException("minimum: " + minimum);
    }
    if (initial < minimum) {
        throw new IllegalArgumentException("initial: " + initial);
    }
    if (maximum < initial) {
        throw new IllegalArgumentException("maximum: " + maximum);
    }

    int minIndex = getSizeTableIndex(minimum);
    if (SIZE_TABLE[minIndex] < minimum) {
        this.minIndex = minIndex + 1;
    } else {
        this.minIndex = minIndex;
    }

    int maxIndex = getSizeTableIndex(maximum);
    if (SIZE_TABLE[maxIndex] > maximum) {
        this.maxIndex = maxIndex - 1;
    } else {
        this.maxIndex = maxIndex;
    }

    this.initial = initial;
}

Specific content of processor implementation class

public Handle newHandle() {
    return new HandleImpl(minIndex, maxIndex, initial);
}

HandleImpl(int minIndex, int maxIndex, int initial) {
    this.minIndex = minIndex;
    this.maxIndex = maxIndex;

    index = getSizeTableIndex(initial);
    nextReceiveBufferSize = SIZE_TABLE[index];
}

Parsing specific subscript parsing of memory value to be allocated

private static int getSizeTableIndex(final int size) {
    for (int low = 0, high = SIZE_TABLE.length - 1;;) {
        if (high < low) {
            return low;
        }
        if (high == low) {
            return high;
        }

        int mid = low + high >>> 1;
        int a = SIZE_TABLE[mid];
        int b = SIZE_TABLE[mid + 1];
        if (size > b) {
            low = mid + 1;
        } else if (size < a) {
            high = mid - 1;
        } else if (size == a) {
            return mid;
        } else {
            return mid + 1;
        }
    }
}

By default, it can read up to 16 times, read 1024 bytes at a time, and allocate the corresponding byteBuf memory.

public ByteBuf allocate(ByteBufAllocator alloc) {
    return alloc.ioBuffer(nextReceiveBufferSize);
}

public ByteBuf ioBuffer(int initialCapacity) {
    if (PlatformDependent.hasUnsafe()) {
        return directBuffer(initialCapacity);
    }
    return heapBuffer(initialCapacity);
}

protected ByteBuf newDirectBuffer(int initialCapacity, int maxCapacity) {
    final ByteBuf buf;
    if (PlatformDependent.hasUnsafe()) {
        buf = noCleaner ? new InstrumentedUnpooledUnsafeNoCleanerDirectByteBuf(this, initialCapacity, maxCapacity) :
                new InstrumentedUnpooledUnsafeDirectByteBuf(this, initialCapacity, maxCapacity);
    } else {
        buf = new InstrumentedUnpooledDirectByteBuf(this, initialCapacity, maxCapacity);
    }
    return disableLeakDetector ? buf : toLeakAwareBuffer(buf);
}

Read message from network channel

protected int doReadBytes(ByteBuf byteBuf) throws Exception {
    return byteBuf.writeBytes(javaChannel(), byteBuf.writableBytes());
}

public abstract class AbstractByteBuf extends ByteBuf
public int writeBytes(ScatteringByteChannel in, int length) throws IOException {
    ensureWritable(length);
    int writtenBytes = setBytes(writerIndex, in, length);
    if (writtenBytes > 0) {
        writerIndex += writtenBytes;
    }
    return writtenBytes;
}

public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
public int setBytes(int index, ScatteringByteChannel in, int length) throws IOException {
    ensureAccessible();
    ByteBuffer tmpBuf = internalNioBuffer();
    tmpBuf.clear().position(index).limit(index + length);
    try {
        return in.read(tmpBuf);
    } catch (ClosedChannelException ignored) {
        return -1;
    }
}