前面谈到在Channel接口内部定义了一个Unsafe接口, 然后有部分方法是直接delagate给unsafe的:

public boolean isWritable() {
    ChannelOutboundBuffer buf = unsafe.outboundBuffer();
    return buf != null && buf.isWritable();
}

Unsafe的概念

Unsafe 是内部接口, 从设计上说这个接口的所有实现都是netty的内部代码,只能被netty自己使用. netty的使用者时不应该 直接调用这些内部实现的.

Unsafe的javadoc是这样要求的:

Unsafe operations that should never be called from user-code. These methods are only provided to implement the actual transport, and must be invoked from an I/O thread except for the following methods:

Unsafe 操作不能被用户代码调用.这些方法仅仅用于实现具体的transport, 而且必须被I/O线程调用.

以下方法例外(可以在I/O线程之外被调用):

invoker()
localAddress()
remoteAddress()
closeForcibly()
register(EventLoop, ChannelPromise)
deregister(ChannelPromise)
voidPromise()

Unsafe 接口定义

Unsafe定义的方法

Unsafe接口中定义了以下方法:

获取特殊属性

RecvByteBufAllocator.Handle recvBufAllocHandle()
ChannelHandlerInvoker invoker()
ChannelOutboundBuffer outboundBuffer()
ChannelPromise voidPromise()

获取网络参数

SocketAddress localAddress()
SocketAddress remoteAddress()

注册到EventLoop

void register(EventLoop eventLoop, ChannelPromise promise)
void deregister(ChannelPromise promise)

IO操作

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 beginRead()
void write(Object msg, ChannelPromise promise)
void flush()

Unsafe的实现

Unsafe的继承结构

以nio unsafe为例:

AbstractUnsafe

在AbstractChannel中定义有内部类AbstractUnsafe, 按照javadoc的说明, 所有的Unsafe的实现都必须从AbstractUnsafe继承:

public abstract class AbstractChannel extends DefaultAttributeMap implements Channel {
    /**
     * {@link Unsafe} implementation which sub-classes must extend and use.
     */
    protected abstract class AbstractUnsafe implements Unsafe {
    }
}

Channel Unsafe