The thread context saves some info about a working thread.
1. thread_id: Current thread id, Auto generated.
2. type: The type is a enum value indicating which type of task current thread is running.
For example: QUERY, LOAD, COMPACTION, ...
3. task id: A unique id to identify this task. maybe query id, load job id, etc.
Using gcc11 compiles thread_local variable on lower versions of GLIBC will report an error, see https://github.com/apache/incubator-doris/pull/7911
This is very difficult to solve, so kudu Class-scoped static thread local implementation was introduced.
Solve the above problem by Thread-scopedthread local + Class-scoped thread local.
See the comments for ThreadContextPtr for details.
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