Sentinel源码学习

从入口开始

在学习使用Sentinel时可以知道，Sentinel的限流入口是Sphu.entry()。那我们就从Sphu.entry()开始，像剥洋葱一样打开Sentinel。

    /**
     * Checking all {@link Rule}s about the resource.
     *
     * @param name the unique name of the protected resource
     * @throws BlockException if the block criteria is met, eg. when any rule's threshold is exceeded.
     */
    public static Entry entry(String name) throws BlockException {
        return Env.sph.entry(name, EntryType.OUT, 1, OBJECTS0);
    }

Env类将触发Sentinel的所有初始化操作。它拥有一个属性sph，这个属性的实现类是CtSph。
进入CtSph类查看entry的实现。

    @Override
    public Entry entry(String name, EntryType type, int count, Object... args) throws BlockException {
        StringResourceWrapper resource = new StringResourceWrapper(name, type);
        return entry(resource, count, args);
    }

在这段代码里首先生成了一个StringResourceWrapper对象。追踪进去发现进入了entryWithPriority方法。

    private Entry entryWithPriority(ResourceWrapper resourceWrapper, int count, boolean prioritized, Object... args)
        throws BlockException {
        Context context = ContextUtil.getContext();
        if (context instanceof NullContext) {
            // The {@link NullContext} indicates that the amount of context has exceeded the threshold,
            // so here init the entry only. No rule checking will be done.
            return new CtEntry(resourceWrapper, null, context);
        }

        if (context == null) {
            // Using default context.
            context = MyContextUtil.myEnter(Constants.CONTEXT_DEFAULT_NAME, "", resourceWrapper.getType());
        }

        // Global switch is close, no rule checking will do.
        if (!Constants.ON) {
            return new CtEntry(resourceWrapper, null, context);
        }

        ProcessorSlot