netty->[組件] ContantPool 以ChannelOption爲例

看看init方法，裏面有兩個對象 ChannelOption和Attribute

    void init(Channel channel) throws Exception {
        ChannelPipeline p = channel.pipeline();
        p.addLast(config.handler());

        final Map<ChannelOption<?>, Object> options = options0();
        synchronized (options) {
            setChannelOptions(channel, options, logger);
        }

        final Map<AttributeKey<?>, Object> attrs = attrs0();
        synchronized (attrs) {
            for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {
                channel.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
            }
        }
    }

 

ChannelOption 這個一般放比較底層的TCP關聯屬性

Attribute 業務屬性值

 

這兩個都是AbstractConstant的子類，看一眼他們的root interface，屬性就一個ID和NAME

abstract class AbstractConstant<T extends AbstractConstant<T>> implements Constant<T>


/**
 * A singleton which is safe to compare via the {@code ==} operator. 
Created and managed by {@link ConstantPool}.
 */
public interface Constant<T extends Constant<T>> extends Comparable<T> {

    /**
     * Returns the unique number assigned to this {@link Constant}.
     */
    int id();

    /**
     * Returns the name of this {@link Constant}.
     */
    String name();
}

瞅一瞅ChannelOption的生成，裏面有一堆靜態的成員變量，獲取實例用valueOf，下面有valueOf的實現

//隨便看下實例
public static final ChannelOption<ByteBufAllocator> ALLOCATOR = valueOf("ALLOCATOR");
    public static final ChannelOption<RecvByteBufAllocator> RCVBUF_ALLOCATOR = valueOf("RCVBUF_ALLOCATOR");
    public static final ChannelOption<MessageSizeEstimator> MESSAGE_SIZE_ESTIMATOR = valueOf("MESSAGE_SIZE_ESTIMATOR");


//看看valueOf方法
public static <T> ChannelOption<T> valueOf(String name) {
        return (ChannelOption<T>) pool.valueOf(name);
}


//調用ConstantPool的valueOf
    public T valueOf(String name) {
        checkNotNullAndNotEmpty(name);
        return getOrCreate(name);
    }

    /**
     * Get existing constant by name or creates new one if not exists. Threadsafe
     *
     * @param name the name of the {@link Constant}
     */
//上面也有netty自己的註釋 說的還是比較清楚的 這個操作 線程安全的
//先去拿 如果存在直接返回 如果不存在 那就生成一個，容器就是一個ConcurrentHashMap
//裏面用了雙重判斷 細細品味 比較美妙的
    private T getOrCreate(String name) {
        T constant = constants.get(name);
        if (constant == null) {
            final T tempConstant = newConstant(nextId(), name);
            constant = constants.putIfAbsent(name, tempConstant);
            if (constant == null) {
                return tempConstant;
            }
        }

        return constant;
    }


//再附上ChannelOption裏面的ContantPool 裏面的newConstant的實現 每個子類都不同 尤其是類型
private static final ConstantPool<ChannelOption<Object>> pool = new ConstantPool<ChannelOption<Object>>() {
        @Override
        protected ChannelOption<Object> newConstant(int id, String name) {
            return new ChannelOption<Object>(id, name);
        }
    };

 

 

下面是賦值代碼

//塞option的代碼

private static void setChannelOption(
            Channel channel, ChannelOption<?> option, Object value, InternalLogger logger) {
        try {
            if (!channel.config().setOption((ChannelOption<Object>) option, value)) {
                ..
            }
        } catch (Throwable t) {
            ..
    }


//defaultChannelConfig裏面的具體實現 option其實只是key，裏面包含了value的類型，賦值的時候會進行校驗
public <T> boolean setOption(ChannelOption<T> option, T value) {
        validate(option, value);
        if (option == CONNECT_TIMEOUT_MILLIS) {
            setConnectTimeoutMillis((Integer) value);
        } else if (option == MAX_MESSAGES_PER_READ) {
            setMaxMessagesPerRead((Integer) value);
        } else if (option == WRITE_SPIN_COUNT) {
            setWriteSpinCount((Integer) value);
        } else if (option == ALLOCATOR) {
            setAllocator((ByteBufAllocator) value);
        } else if (option == RCVBUF_ALLOCATOR) {
            setRecvByteBufAllocator((RecvByteBufAllocator) value);
        } else if (option == AUTO_READ) {
            setAutoRead((Boolean) value);
        } else if (option == AUTO_CLOSE) {
            setAutoClose((Boolean) value);
        } else if (option == WRITE_BUFFER_HIGH_WATER_MARK) {
            setWriteBufferHighWaterMark((Integer) value);
        } else if (option == WRITE_BUFFER_LOW_WATER_MARK) {
            setWriteBufferLowWaterMark((Integer) value);
        } else if (option == WRITE_BUFFER_WATER_MARK) {
            setWriteBufferWaterMark((WriteBufferWaterMark) value);
        } else if (option == MESSAGE_SIZE_ESTIMATOR) {
            setMessageSizeEstimator((MessageSizeEstimator) value);
        } else if (option == SINGLE_EVENTEXECUTOR_PER_GROUP) {
            setPinEventExecutorPerGroup((Boolean) value);
        } else {
            return false;
        }
        return true;
    }