Function ping_host 

pub fn ping_host(
    alias: String,
    hostname: String,
    port: u16,
    tx: Sender<AppEvent>,
    generation: u64,
)

Ping a single host by attempting a TCP connection on the configured port. Sends the result back via the channel.

DNS resolution runs in a nested thread with a 5s timeout via recv_timeout. If DNS hangs beyond 5s, the outer thread reports unreachable and exits, but the inner thread may linger until the OS DNS resolver times out (typically 30-60s). This is inherent to blocking to_socket_addrs with no cancellation support. Repeated pings to hosts with broken DNS can temporarily accumulate threads, but they will self-clean once the OS resolver gives up.