Steps to reproduce:
1. Load template from attachment (zbx_export_templates(1).xml );
2. Load 5 hosts from attachment (zbx_export_hosts(3).xml );
3. Start server with 5 lld workers (reproduces also on 2);
4. Start scripts running for 5 hosts in parallel;

./send_discovery.sh host.01 1000 &
./send_discovery.sh host.02 1000 &
./send_discovery.sh host.03 1000 &
./send_discovery.sh host.04 1000 &
./send_discovery.sh host.05 1000 &

5. Wait for deadlock reported in log;