初学者的Erlang / OTP行为 [英] Erlang/OTP behaviors for beginner
问题描述
正如我从Erlang和OTP in action一书中所理解的，行为一词是指：
As I understood from the "Erlang and OTP in action" book, the word behavior refers to:
- 行为界面是一组函数;
- 行为实现，它是应用程序特定的代码（回调模块）;
- 行为容器是一个过程。
问题：
Erlang / OTP初学者应该了解什么行为？是否可以简单地描述和理解OTP行为的概念？
什么'回调函数' Elang / OTP？
我们可以将行为实现中的回调视为在Java中覆盖的方法吗？
Can we consider the callbacks in a behaviour implemenation as methods overriden in Java?
这本书说，下面代码中库函数gen_server：start_link / 4的相关回调函数是Module：init / 1。
The book says that the associated callback function for the library function 'gen_server:start_link/4' in the following code is 'Module:init/1'.
这是否意味着使用init / 1我们调用gen_server：start_link / 4库函数？或者这是否意味着什么？
Does that mean that with init/1 we call the gen_server:start_link/4 library function? Or does that mean anything else?
-module(tr_server).
-behaviour(gen_server).
-include_lib("eunit/include/eunit.hrl").
%% API
-export([
start_link/1,
start_link/0,
get_count/0,
stop/0
]).
%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-define(SERVER, ?MODULE).
-define(DEFAULT_PORT, 1055).
-record(state, {port, lsock, request_count = 0}).
%%%===================================================================
%%% API
%%%===================================================================
%%--------------------------------------------------------------------
%% @doc Starts the server.
%%
%% @spec start_link(Port::integer()) -> {ok, Pid}
%% where
%% Pid = pid()
%% @end
%%--------------------------------------------------------------------
start_link(Port) ->
gen_server:start_link({local, ?SERVER}, ?MODULE, [Port], []).
%% @spec start_link() -> {ok, Pid}
%% @doc Calls `start_link(Port)' using the default port.
s tart_link() ->
start_link(?DEFAULT_PORT).
%%--------------------------------------------------------------------
%% @doc Fetches the number of requests made to this server.
%% @spec get_count() -> {ok, Count}
%% where
%% Count = integer()
%% @end
%%--------------------------------------------------------------------
get_count() ->
gen_server:call(?SERVER, get_count).
%%--------------------------------------------------------------------
%% @doc Stops the server.
%% @spec stop() -> ok
%% @end
%%--------------------------------------------------------------------
stop() ->
gen_server:cast(?SERVER, stop).
%%%===================================================================
%%% gen_server callbacks
%%%===================================================================
init([Port]) ->
{ok, LSock} = gen_tcp:listen(Port, [{active, true}]),
{ok, #state{port = Port, lsock = LSock}, 0}.
handle_call(get_count, _From, State) ->
{reply, {ok, State#state.request_count}, State}.
handle_cast(stop, State) ->
{stop, normal, State}.
handle_info({tcp, Socket, RawData}, State) ->
do_rpc(Socket, RawData),
RequestCount = State#state.request_count,
{noreply, State#state{request_count = RequestCount + 1}};
handle_info(timeout, #state{lsock = LSock} = State) ->
{ok, _Sock} = gen_tcp:accept(LSock),
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
%%%===================================================================
%%% Internal functions
%%%===================================================================
do_rpc(Socket, RawData) ->
try
{M, F, A} = split_out_mfa(RawData),
Result = apply(M, F, A),
gen_tcp:send(Socket, io_lib:fwrite("~p~n", [Result]))
catch
_Class:Err ->
gen_tcp:send(Socket, io_lib:fwrite("~p~n", [Err]))
end.
split_out_mfa(RawData) ->
MFA = re:replace(RawData, "\r\n$", "", [{return, list}]),
{match, [M, F, A]} =
re:run(MFA,
"(.*):(.*)\s*\\((.*)\s*\\)\s*.\s*$",
[{capture, [1,2,3], list}, ungreedy]),
{list_to_atom(M), list_to_atom(F), args_to_terms(A)}.
args_to_terms(RawArgs) ->
{ok, Toks, _Line} = erl_scan:string("[" ++ RawArgs ++ "]. ", 1),
{ok, Args} = erl_parse:parse_term(Toks),
Args.
%% test
start_test() ->
{ok, _} = tr_server:start_link(1055).
推荐答案
Q ： Erlang / OTP初学者应该了解哪些行为？是
可以描述和理解
简要中OTP行为的概念吗？
Q: What an Erlang/OTP beginner should know about behaviours? Is it possible to describe and understand the notion of OTP behaviour in a nutshell?
通常在代码中使用，以便编译器可以根据其行为生成更直观的错误消息，即application / supervisor / gen_server / gen_event / gen_fsm。
A behaviour is usually used in code so that the compiler can generate more intuitive error messages depending upon its behaviour i.e application/supervisor/gen_server/gen_event/gen_fsm.
特定于ex：gen_server行为的邮件
It enables the compiler give error messages specific to the behaviour for ex: gen_server
问：什么'回调函数'上下文
Elang / OTP？
Q: What 'callback function' does actually mean in the context of Elang/OTP?
回调函数可以说是从GUI编程（至少类似）。每当事件发生时。鼠标点击有一个单独的函数处理鼠标点击。
Callback function can be said to be taken from GUI programming (at least similar). Whenever an event occurs for ex. a mouse click there is a separate function that handles mouse click.
因此，例如。 gen_server的导出函数从另一个模块调用，该函数可以具有不同模式的回调函数（handle_call / handle_cast）。
Thus whenever for eg. an exported function of a gen_server is called from another module, that function can have a callback function (handle_call/handle_cast) having different patterns.
问：我们可以将行为实现中的回调视为在Java中覆写的方法
吗？
Q: Can we consider the callbacks in a behaviour implementation as methods overridden in Java?
Yeah ... maybe ... no：）
Yeah...maybe...no :)
问：这本书说相关的回调函数库
函数'gen_server：start_link / 4'在下面的代码是
'模块：init / 1'。
Q: The book says that the associated callback function for the library function 'gen_server:start_link/4' in the following code is 'Module:init/1'.
gen_server：start_link自己调用init函数，由w55 ....回答。（对不起大的名字）。
gen_server:start_link calls init function by itself as answered by w55.... (sorry quite a big name).
希望我已回答了您的所有问题：）
Hope I have answered all your queries :)
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