When the table is stopped, all compaction groups
are stopped, and as part of that, they are flushing
their memtables.
To synchronize with stop-induced flush operation,
move _pending_flushes_phaser.stop() later in table::stop(),
after all compaction groups are flushed and stopped.
This way, in table::flush, if we see that the phaser
is already closed, we know that there is nothing to flush,
otherwise we start a flush operation that would be waited
on by a parallel table::stop().
Fixes#22243
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Closesscylladb/scylladb#22339
23284f038f