InnoDB supports row-level locking. Selected rows can be locked using LOCK IN
SHARE MODE or FOR UPDATE. In both cases, a lock is acquired on the rows read
by the query, and it will be released when the current transaction is
committed.

When LOCK IN SHARE MODE is specified in a SELECT statement, MariaDB will wait
until all transactions that have modified the rows are committed. Then, a
write lock is acquired. All transactions can read the rows, but if they want
to modify them, they have to wait until your transaction is committed.

If autocommit is set to 1 (the default), the LOCK IN SHARE MODE and FOR UPDATE
clauses have no effect.

URL: https://mariadb.com/kb/en/lock-in-share-mode/