sentinel springwebmvc不支持异步async请求

我们在Controller使用了WebAsyncTask的异步返回方式，这种情况下，AbstractSentinelInterceptor中的prehandle会执行两次，rckey变成了2，但是afterCompletion只会执行一次（而且还是在另外一个线程请求的），导致clean的逻辑无法执行，这样entry和context在threadlocal中一直无法清除，最终oom

Start by tracing WebAsyncTask handling through AbstractSentinelInterceptor, especially the preHandle and afterCompletion callbacks and their ThreadLocal cleanup. Reproduce the asynchronous request and verify that repeated interception and completion on another thread do not leave entry or context state behind.

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