Summary:
WritePreparedTxnDB calls CancelAllBackgroundWork in its destructor to avoid dangling references to it from background job's SnapshotChecker callback. However, if the DBImpl is already closed, the info log might be closed with it, which causes memory leak when CancelAllBackgroundWork tries to print to the info log. The patch fixes that by calling CancelAllBackgroundWork only if the db is not closed already.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6268
Differential Revision: D19303439
Pulled By: maysamyabandeh
fbshipit-source-id: 4228a6be7e78d43c90630347baa89b008200bd15