commit 38fd7b7d917

Author: Marko Mäkelä <marko.makela@mariadb.com>

Date:   Fri Dec 4 16:18:04 2020 +0200

    MDEV-21452: Replace all direct use of os_event_t

    Let us replace os_event_t with mysql_cond_t, and replace the

    necessary ib_mutex_t with mysql_mutex_t so that they can be

    used with condition variables.

    Also, let us replace polling (os_thread_sleep() or timed waits)

    with plain mysql_cond_wait() wherever possible.

    Furthermore, we will use the lightweight srw_mutex for trx_t::mutex,

    to hopefully reduce contention on lock_sys.mutex.

    FIXME: Add test coverage of

    mariabackup --backup --kill-long-queries-timeout