Summary:
Before this PR, `get_iostats_context()` will silently return a nullptr if no thread_local support is detected.
This can be the result of build_detect_platform's failure to compile the simple code snippet on certain platforms, as
reported in https://github.com/facebook/mysql-5.6/issues/904.
To be safe, we should fail the compilation if user does not opt out IOStatsContext and
ROCKSDB_SUPPORT_THREAD_LOCAL is not defined.
If RocksDB relies on c++11, can we just always use thread_local? It turns out there might be
performance concerns (https://github.com/facebook/rocksdb/issues/5774),
which is beyond the scope of this PR. We can revisit this later. Here, we stick to the original impl.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8117
Reviewed By: ajkr
Differential Revision: D27356847
Pulled By: riversand963
fbshipit-source-id: f7d5776842277598d8341b955febb601946801ae
fd00f39f97