官方文档

https://sentinelguard.io/zh-cn/docs/basic-implementation.html

初始化时机

   // 1.5.0 版本开始可以直接利用 try-with-resources 特性 自动回收调用  entry.exit() 配合注解使用 @SentinelResource("HelloWorld")
                        try (Entry entry = SphU.entry(
                            "HelloWorld",
                            EntryType.IN)) {
                            // 被保护的逻辑
                            System.out.println(Thread.currentThread().getId() + "hello world" + (++i));

                        } catch (BlockException ex) {
                            i++;
                        }

com.alibaba.csp.sentinel.SphU#entry(java.lang.String, com.alibaba.csp.sentinel.EntryType)

    public static Entry entry(String name, EntryType trafficType) throws BlockException {
        return Env.sph.entry(name, trafficType, 1, OBJECTS0);
    }

com.alibaba.csp.sentinel.CtSph#entry(java.lang.String, com.alibaba.csp.sentinel.EntryType, int, java.lang.Object...)

   @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);
    }

com.alibaba.csp.sentinel.CtSph#entryWithPriority(com.alibaba.csp.sentinel.slotchain.ResourceWrapper, int, boolean, java.lang.Object...)

 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 = InternalContextUtil.internalEnter(Constants.CONTEXT_DEFAULT_NAME);
        }

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

        ProcessorSlot<Object> chain = lookProcessChain(resourceWrapper);

        /*
         * Means amount of resources (slot chain) exceeds {@link Constants.MAX_SLOT_CHAIN_SIZE},
         * so no rule checking will be done.
         */
        if (chain == null) {
            return new CtEntry(resourceWrapper, null, context);
        }

        Entry e = new CtEntry(resourceWrapper, chain, context);
        try {
            chain.entry(context, resourceWrapper, null, count, prioritized, args);
        } catch (BlockException e1) {
            e.exit(count, args);
            throw e1;
        } catch (Throwable e1) {
            // This should not happen, unless there are errors existing in Sentinel internal.
            RecordLog.info("Sentinel unexpected exception", e1);
        }
        return e;
    }

com.alibaba.csp.sentinel.CtSph#lookProcessChain

 ProcessorSlot<Object> lookProcessChain(ResourceWrapper resourceWrapper) {
        ProcessorSlotChain chain = chainMap.get(resourceWrapper);
        if (chain == null) {
            synchronized (LOCK) {
                chain = chainMap.get(resourceWrapper);
                if (chain == null) {
                    // Entry size limit.
                    if (chainMap.size() >= Constants.MAX_SLOT_CHAIN_SIZE) {
                        return null;
                    }

                    chain = SlotChainProvider.newSlotChain();
                    Map<ResourceWrapper, ProcessorSlotChain> newMap = new HashMap<ResourceWrapper, ProcessorSlotChain>(
                        chainMap.size() + 1);
                    newMap.putAll(chainMap);
                    newMap.put(resourceWrapper, chain);
                    chainMap = newMap;
                }
            }
        }
        return chain;
    }

com.alibaba.csp.sentinel.slotchain.SlotChainProvider#newSlotChain

    public static ProcessorSlotChain newSlotChain() {
        if (slotChainBuilder != null) {
            return slotChainBuilder.build();
        }

        // Resolve the slot chain builder SPI.
        slotChainBuilder = SpiLoader.loadFirstInstanceOrDefault(SlotChainBuilder.class, DefaultSlotChainBuilder.class);

        if (slotChainBuilder == null) {
            // Should not go through here.
            RecordLog.warn("[SlotChainProvider] Wrong state when resolving slot chain builder, using default");

            slotChainBuilder = new DefaultSlotChainBuilder();
        } else {
            RecordLog.info("[SlotChainProvider] Global slot chain builder resolved: "
                + slotChainBuilder.getClass().getCanonicalName());
        }
        return slotChainBuilder.build();
    }

    private SlotChainProvider() {}
}