聊聊sentinel的DefaultSlotsChainBuilder

序

本文主要研究一下sentinel的DefaultSlotsChainBuilder

DefaultSlotsChainBuilder

com/alibaba/csp/sentinel/slots/DefaultSlotsChainBuilder.java

public class DefaultSlotsChainBuilder implements SlotsChainBuilder {

    @Override
    public ProcessorSlotChain build() {
        ProcessorSlotChain chain = new DefaultProcessorSlotChain();
        chain.addLast(new NodeSelectorSlot());
        chain.addLast(new ClusterBuilderSlot());
        chain.addLast(new LogSlot());
        chain.addLast(new StatisticSlot());
        chain.addLast(new SystemSlot());
        chain.addLast(new AuthoritySlot());
        chain.addLast(new FlowSlot());
        chain.addLast(new DegradeSlot());

        return chain;
    }

}

• 實現build方法，返回DefaultProcessorSlotChain，經過它addLast方法構造鏈式調用

DefaultProcessorSlotChain

com/alibaba/csp/sentinel/slotchain/DefaultProcessorSlotChain.java

public class DefaultProcessorSlotChain extends ProcessorSlotChain {

    AbstractLinkedProcessorSlot<?> first = new AbstractLinkedProcessorSlot<Object>() {

        @Override
        public void entry(Context context, ResourceWrapper resourceWrapper, Object t, int count, Object... args)
            throws Throwable {
            super.fireEntry(context, resourceWrapper, t, count, args);
        }

        @Override
        public void exit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
            super.fireExit(context, resourceWrapper, count, args);
        }

    };
    AbstractLinkedProcessorSlot<?> end = first;

    @Override
    public void addFirst(AbstractLinkedProcessorSlot<?> protocolProcessor) {
        protocolProcessor.setNext(first.getNext());
        first.setNext(protocolProcessor);
        if (end == first) {
            end = protocolProcessor;
        }
    }

    @Override
    public void addLast(AbstractLinkedProcessorSlot<?> protocolProcessor) {
        end.setNext(protocolProcessor);
        end = protocolProcessor;
    }

    /**
     * Same as {@link #addLast(AbstractLinkedProcessorSlot)}.
     *
     * @param next processor to be added.
     */
    @Override
    public void setNext(AbstractLinkedProcessorSlot<?> next) {
        addLast(next);
    }

    @Override
    public AbstractLinkedProcessorSlot<?> getNext() {
        return first.getNext();
    }

    @Override
    public void entry(Context context, ResourceWrapper resourceWrapper, Object t, int count, Object... args)
        throws Throwable {
        first.transformEntry(context, resourceWrapper, t, count, args);
    }

    @Override
    public void exit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
        first.exit(context, resourceWrapper, count, args);
    }

}

• 主要有兩個屬性，一個是first，一個是end，它們是AbstractLinkedProcessorSlot類型
• 方法主要有addFirst，addLast，setNext
• 這裏默認設置了first，以後主要是經過getNext方法來開啓鏈式調用，getNext方法返回的是first的next

AbstractLinkedProcessorSlot

com/alibaba/csp/sentinel/slotchain/AbstractLinkedProcessorSlot.java

public abstract class AbstractLinkedProcessorSlot<T> implements ProcessorSlot<T> {

    private AbstractLinkedProcessorSlot<?> next = null;

    @Override
    public void fireEntry(Context context, ResourceWrapper resourceWrapper, Object obj, int count, Object... args)
        throws Throwable {
        if (next != null) {
            next.transformEntry(context, resourceWrapper, obj, count, args);
        }
    }

    @SuppressWarnings("unchecked")
    void transformEntry(Context context, ResourceWrapper resourceWrapper, Object o, int count, Object... args)
        throws Throwable {
        T t = (T)o;
        entry(context, resourceWrapper, t, count, args);
    }

    @Override
    public void fireExit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
        if (next != null) {
            next.exit(context, resourceWrapper, count, args);
        }
    }

    public AbstractLinkedProcessorSlot<?> getNext() {
        return next;
    }

    public void setNext(AbstractLinkedProcessorSlot<?> next) {
        this.next = next;
    }

}

• AbstractLinkedProcessorSlot是全部slot的基類，有個next屬性，用來標識下一個slot
• entry是整個鏈式調用的入口，默認是會觸發fireEntry，經過判斷next不爲null，則調用next的transformEntry，進而調用next的entry方法
• 子類的entry方法會作一些前置校驗工做，經過以後調用fireEntry方法，進而完成整個鏈式調用

小結

sentinel使用了責任鏈模式來進行各類slot邏輯的執行，其構建是經過DefaultSlotsChainBuilder來進行build。

doc

• slotchain