Example: Initializing without guaranteeing connections

示例：没有保证连接的初始化

The following code attempts to guarantee a connection as part of the process’ state:

----------------------------------------------------------------------------------
1 init(Args) ->
2 Opts = parse_args(Args),
3 {ok, Port} = connect(Opts),
4 {ok, #state{sock=Port, opts=Opts}}.
5
6 [...]
7
8 handle_info(reconnect, S = #state{sock=undefined, opts=Opts}) ->
9 %% try reconnecting in a loop
10 case connect(Opts) of
11 {ok, New} -> {noreply, S#state{sock=New}};
12 _ -> self() ! reconnect, {noreply, S}
13 end;
----------------------------------------------------------------------------------
 Instead, consider rewriting it as:

----------------------------------------------------------------------------------
1 init(Args) ->
2 Opts = parse_args(Args),
3 %% you could try connecting here anyway, for a best
4%% effort thing, but be ready to not have a connection.
5 self() ! reconnect,
6{ok, #state{sock=undefined, opts=Opts}}.
7
8 [...]
9
10handle_info(reconnect, S = #state{sock=undefined, opts=Opts}) ->
11%% try reconnecting in a loop
12case connect(Opts) of
13{ok, New} -> {noreply, S#state{sock=New}};
14_ -> self() ! reconnect, {noreply, S}
15end;
----------------------------------------------------------------------------------
You now allow initializations with fewer guarantees: they went from the connection is available to the connection manager is available.