Kea freezes on config reload when using host commands and host database.

Kea freezes during configuration reload. Last log message: DHCPSRV_TIMERMGR_START_TIMER starting timer: memfile-lfc.

This behavior is random. It occurs about 75% of the time when I try to trigger it with the same steps. On about 25% of runs, Kea reconfigures correctly and runs normally.

It happens on both MySQL and PostgreSQL.

Steps to reproduce:

1. Run kea with /sbin/keactrl start using the config file provided below.
2. Reconfigure kea by running /sbin/keactrl reload (you can use the same configuration file)
3. Kea freezes on DHCPSRV_TIMERMGR_START_TIMER starting timer: memfile-lfc - Kea does not respond to the control agent or DHCP traffic.

Configuration required to trigger freeze: hooks-libraries: libdhcp_mysql.so(or libdhcp_pgsql.so),libdhcp_host_cmds.so ; and configured hosts-database.

You can omit libdhcp_host_cmds.so in the config file used to reload, and a freeze will still occur, but it has to be present in the original config used to start Kea.

I did not test if keactrl is required to trigger freeze.

Simpliest config that triggers the freeze:

{
    "Dhcp4": {
        "hooks-libraries": [
            {
                "library": "/home/mgodzina/installed/keadev/lib/kea/hooks/libdhcp_mysql.so"
            },
            {
                "library": "/home/mgodzina/installed/keadev/lib/kea/hooks/libdhcp_host_cmds.so"
            }
        ],
        "hosts-database": {
            "host": "",
            "name": "keadb",
            "password": "keapass",
            "type": "mysql",
            "user": "keauser"
        },
        "interfaces-config": {
            "interfaces": [
                "enp0s9"
            ]
        },
        "lease-database": {
            "type": "memfile"
        },
        "loggers": [
            {
                "debuglevel": 99,
                "name": "kea-dhcp4",
                "output-options": [
                    {
                        "output": "/home/mgodzina/installed/keadev/var/log/kea.log"
                    }
                ],
                "severity": "DEBUG"
            }
        ],
        "option-data": [],
        "rebind-timer": 2000,
        "renew-timer": 1000,
        "shared-networks": [],
        "valid-lifetime": 4000
    }
}

Log file:

kea.log