[编织消息框架][netty源码分析]7 Unsafe 实现类NioSocketChannelUnsafe职责与实现

Unsafe 是channel的内部接口， 负责跟socket底层打交道。从书写跟命名上看是不公开给开发者使用的，直到最后实现NioSocketChannelUnsafe也没有公开出去

public interface Channel extends AttributeMap, ChannelOutboundInvoker, Comparable<Channel> {
    interface Unsafe {
        RecvByteBufAllocator.Handle recvBufAllocHandle();
        SocketAddress localAddress();
        SocketAddress remoteAddress();
        void register(EventLoop eventLoop, ChannelPromise promise);
        void bind(SocketAddress localAddress, ChannelPromise promise);
        void connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise);
        void disconnect(ChannelPromise promise);
        void close(ChannelPromise promise);
        void closeForcibly();
        void deregister(ChannelPromise promise);
        void beginRead();
        void write(Object msg, ChannelPromise promise);
        void flush();
        ChannelPromise voidPromise();
        ChannelOutboundBuffer outboundBuffer();
    }
    public interface NioUnsafe extends Unsafe {
        SelectableChannel ch();
        void finishConnect();
        void read();
        void forceFlush();
    }
}

NioSocketChannelUnsafe 继承关系为： NioSocketChannelUnsafe -> NioByteUnsafe -> AbstractNioUnsafe -> AbstractUnsafe

AbstractUnsafe：负责socket 链路绑定、接受、关闭，数据fush操作

每个操作大概分四个阶段处理

        @Override
        public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
            assertEventLoop();
            //执行前检查
            if (!promise.setUncancellable() || !ensureOpen(promise)) {
                return;
            }

            boolean wasActive = isActive();
            //调用实现
            try {
                doBind(localAddress);
            } catch (Throwable t) {
                safeSetFailure(promise, t);
                closeIfClosed();
                return;
            }

            //调用业务,通知pipeline
            if (!wasActive && isActive()) {
                invokeLater(()-> pipeline.fireChannelActive(););
            }
            //完成阶段处理
            safeSetSuccess(promise);
        }

 @Override
        public final void flush() {
            assertEventLoop();

            ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;
            if (outboundBuffer == null) {
                return;
            }

            outboundBuffer.addFlush();
            flush0();
        }

        @SuppressWarnings("deprecation")
        protected void flush0() {
            //刚完成Flush操作
            if (inFlush0) {
                 return;
            }

            final ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;
            if (outboundBuffer == null || outboundBuffer.isEmpty()) {
                return;
            }

            inFlush0 = true;

            //发送数据前链路检查
            if (!isActive()) {
                try {
                    if (isOpen()) {
                        //true 通知 handler channelWritabilityChanged方法
                        outboundBuffer.failFlushed(FLUSH0_NOT_YET_CONNECTED_EXCEPTION, true);
                    } else {
                        outboundBuffer.failFlushed(FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
                    }
                } finally {
                    inFlush0 = false;
                }
                return;
            }

            try {
                //调用channel实现
                doWrite(outboundBuffer);
            } catch (Throwable t) {
                if (t instanceof IOException && config().isAutoClose()) {
                    close(voidPromise(), t, FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
                } else {
                    outboundBuffer.failFlushed(t, true);
                }
            } finally {
                inFlush0 = false;
            }
        }

AbstractNioUnsafe：是NioUnsafe接口模板类，简单的包装

NioByteUnsafe：主要对NioUnsafe接口 read操作实现

NioSocketChannelUnsafe:只是简单的包装，最终公开给内部使用

NioByteUnsafe read方法

      public final void read() {
            final ChannelConfig config = config();
            final ChannelPipeline pipeline = pipeline();
            final ByteBufAllocator allocator = config.getAllocator();
            final RecvByteBufAllocator.Handle allocHandle = recvBufAllocHandle();
            allocHandle.reset(config);

            ByteBuf byteBuf = null;
            boolean close = false;
            try {
                do {
                    byteBuf = allocHandle.allocate(allocator);
                    //填充byteBuf 调用channel实现
                    int size = doReadBytes(byteBuf);
                    //记录最后读取长度
                    allocHandle.lastBytesRead(size);
                    //链路关闭，释放byteBuf
                    if (allocHandle.lastBytesRead() <= 0) {
                        byteBuf.release();
                        byteBuf = null;
                        close = allocHandle.lastBytesRead() < 0;
                        break;
                    }
                    //自增消息读取处理次数
                    allocHandle.incMessagesRead(1);
                    //已完成填充byteBuf 调用业务pipeline
                    readPending = false;
                    pipeline.fireChannelRead(byteBuf);
                    byteBuf = null;
                } while (allocHandle.continueReading());

                allocHandle.readComplete();
                pipeline.fireChannelReadComplete();

                if (close) {
                    closeOnRead(pipeline);
                }
            } catch (Throwable t) {
                handleReadException(pipeline, byteBuf, t, close, allocHandle);
            } finally {
                //如果不是主动read 要完成后要清理read op
                if (!readPending && !config.isAutoRead()) {
                    removeReadOp();
                }
            }
        }
    }

小结：可以看出没有任何的计算代码，Unsafe只实现边界检查、流程控制，具体实现交给上层处理