sqlite3_mutex *sqlite3_db_mutex(sqlite3*);
This interface returns a pointer the sqlite3_mutex object that serializes access to the database connection given in the argument when the threading mode is Serialized. If the threading mode is Single-thread or Multi-thread then this routine returns a NULL pointer.
See also lists of Objects, Constants, and Functions.
SQLite is in the Public Domain.
https://sqlite.org/c3ref/db_mutex.html