Sentinel的秘书Context上下文

package com.alibaba.csp.sentinel.context;
/**
 * Utility class to get or create {@link Context} in current thread.
 * Each {@link SphU}#entry() or {@link SphO}#entry() should be in a {@link Context}.
 * If we don't invoke {@link ContextUtil}#enter() explicitly, DEFAULT context will be used.
 */
public class ContextUtil {
              /*省略部分代码。。。。。。*/
    static {
        // Cache the entrance node for default context.
        initDefaultContext();
    }

    private static void initDefaultContext() {
        String defaultContextName = Constants.CONTEXT_DEFAULT_NAME;
       /*初始化一个sentinel_default_context，type为in的队形*/
        EntranceNode node = new EntranceNode(new StringResourceWrapper(defaultContextName, EntryType.IN), null);
       /*Constants.ROOT会初始化一个name是machine-root，type=IN的对象*/
        Constants.ROOT.addChild(node);
       /*map添加key=CONTEXT_DEFAULT_NAME的对象*/
        contextNameNodeMap.put(defaultContextName, node);
    }
}
             /*省略部分代码。。。。。。*/

protected static Context trueEnter(String name, String origin) {
        Context context = contextHolder.get();
        if (context == null) {
            Map<String, DefaultNode> localCacheNameMap = contextNameNodeMap;
            /*在contextNameNodeMap中查找是否有已存在的node*/
            DefaultNode node = localCacheNameMap.get(name);
            if (node == null) {
                if (localCacheNameMap.size() > Constants.MAX_CONTEXT_NAME_SIZE) {
                    setNullContext();
                    return NULL_CONTEXT;
                } else {
                    try {
                        LOCK.lock();
                 /*类似initDefaultContext方法的内容，但不一样*/
                        node = contextNameNodeMap.get(name);
                        if (node == null) {
                            if (contextNameNodeMap.size() > Constants.MAX_CONTEXT_NAME_SIZE) {
                                setNullContext();
                                return NULL_CONTEXT;
                            } else {
                 /*此处创建的node名字为ContextUtil.enter中的name*/
                                node = new EntranceNode(new StringResourceWrapper(name, EntryType.IN), null);
                                /*以下代码提升迭代稳定性，防止脏读*/
                                Constants.ROOT.addChild(node);
                                Map<String, DefaultNode> newMap = new HashMap<>(contextNameNodeMap.size() + 1);
                                newMap.putAll(contextNameNodeMap);
                                newMap.put(name, node);
                                contextNameNodeMap = newMap;
                            }
                        }
                    } finally {
                        LOCK.unlock();
                    }
                }
            }
            context = new Context(node, name);
            context.setOrigin(origin);
            contextHolder.set(context);
        }
        return context;
    }