Is it necessary to close the database connnection explicitly and how

[Betristor]

I'm using SQLite to record results from repeated optimization results. Each run a result will be appended to the database file but sometimes results are dropped and no error occurred when parallel processes go on. I enabled the WAL mode of SQLite to avoid locked database error but still some results are missing for random. I was suggested to close the database connection in each thread but there is no description about the close function. Now I'm curious about the close action and when and how to do it. Is there any paradigm to follow?