If several threads change the flags at the same time, the result is undefined.

Handles should only be closed by a single thread, and only if no other threads are going to reference the database handle or one of its cursors any further. Do not close a handle if an existing transaction has modified its database. Doing so can cause misbehavior from database corruption to errors like MDB_BAD_VALSIZE (since the DB name is gone).

This flag must not be specified if the database was opened with MDB_DUPSORT.

Do not mix processes with and without MDB_WRITEMAP on the same environment

This function must not be called from multiple concurrent transactions in the same process.