private static String buildRecipientListString(SendContext ctx) {
        return ctx.recipients.stream().map(r -> {
            if (!(r.getServiceAddress() instanceof RPCServiceAddress addr)) {
                return "<non-RPC service address>";
            }
            return String.format("%s at %s", addr.getServiceName(), addr.getConnectionSpec());
        }).collect(Collectors.joining(", "));
    }
The network uses a cache of RPC targets (see {@link RPCTargetPool}) that allows it to save time by reusing open
connections. It works by keeping a set of the most recently used targets open. Calling this method forces all
unused connections to close immediately.
messagebus/src/main/java/com/yahoo/messagebus/network/rpc/RPCNetwork.java