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Describe the proposal

En:Generally, in Java, traceid and spanid are passed through the thread context, but in the case of multi-threading, there will be multiple thread contexts. At this time, the chain will be lost when the same request reaches the child thread. At this time, we need to copy the link data from one thread to the context of another thread. If you don’t know how to copy, you can consider how to share data between threads, such as using shared variables such as member variables.

中文：一般在Java中traceid和spanid我们都是通过线程上下文来传递的但是出现了多线程的情况下就会有多个线程上下文的情况，这个时候就会导致同一个请求中到了子线程时候丢失了链路追踪数据，这个时候就需要我们将链路数据从一个线程拷贝到另外一个线程的上下文中，如果不知道如何拷贝可以考虑下线程间是如何共享数据的比如使用成员变量这种共享变量