Function try_send 

pub fn try_send(
    ctx: &ServiceContext,
    peer: &str,
    msg: &Message,
) -> Result<(), Error>

Send to a service by NAME, refusing rather than waiting if its queue is full.

Error::Busy means the message was NOT queued and nothing happened. This is the direction that breaks a mutual-send deadlock, and the one a server uses to answer a client.