Summary:
The FsyncFiles background job call Fsync() periodically for blob files. However it can access WritableFileWriter concurrently with a Put() or Write(). And WritableFileWriter does not support concurrent access. It will lead to WritableFileWriter buffer being flush with same content twice, and blob file end up corrupted. Fixing by simply let FsyncFiles hold write_mutex_.
Closes https://github.com/facebook/rocksdb/pull/2685
Differential Revision: D5561908
Pulled By: yiwu-arbug
fbshipit-source-id: f0bb5bcab0e05694e053b8c49eab43640721e872
0d4a2b7330