Task manager lockup during shutdown
In https://gitlab.isc.org/isc-projects/bind9/-/jobs/280483, named locked up during shutdown in the rndc system test (though I believe the problem is a generic one).
Looking at the core dump, it appears that by the time isc_thread_join() is called in a loop inside isc_taskmgr_destroy(), at least the first worker thread (i == 0) has not yet woken up and is still waiting for the work_available condition variable to be signalled (which wake_all_queues() should have taken care of). Both the ready_tasks and ready_priority_tasks lists for manager->queues[0] are empty.
I am reporting this in case it turns out to be another glitch caused by !2132 (closed) (0f9be4ae?).