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The mysys timer (thr_timer) could deadlock with srv_thread_pool_end() due to lock inversion: - LOCK_timer is held during the entire timer action routine. - timer action executed in mysys thread may lock timer_generic::m_mtx. - main thread holding the same timer_generic::m_mtx calls thr_timer_end(), which also needs LOCK_timer. This inversion can cause a very rare shutdown deadlock, when the threadpool extends the maintenance() period after idling for a minute and shutdown occurs simultaneously. Workaround: Use try_lock in timer_generic::set_period() to avoid blocking, to break the deadlock cycle, and ignore errors. Root cause is the thr_timer holds the global LOCK_timer for the entire duration of every timer action. This makes it difficult or impossible to use additional locks safely inside timer routines. Fortunately, in this case a failed try_lock has no impact.