In AutoVacWorkerMain(), the code calls on_shmem_exit(FreeWorkInfo,0) and
then kill() to send SIGUSR2 to autovacuum launcher process. In
FreeWorkInfo() it sets AutoVacuumShmem->av_signal[AutoVacRebalance] = true.
But, is it possible that when autovacuum launcher’s SIGUSR2 handler checks
av_signal[AutoVacRebalance], FreeWorkInfo() haven’t set this flag yet and
thus autovacuum launcher will miss the AutoVacRebalance event?