erlang - gen_server:使用新状态调用
问题描述
一个模块调用 agen_server
来处理一个流,它使用记录作为状态。
handle_call
使用 from 的函数处理流State
,该函数将完成的数据和尾部分开,
State
现在下一次,在模块发送更多数据之前,应该先馈送尾部,但要更新。
handle_call({stream, Data}, _From, State = #mystate{myfun=Fun}) ->
case Fun(Data) of
{completed piece,tail} ->
dosomethingwithpieace,
NewState = State##mystate{myfun=resetfun()};
% How do i call this again to feed Tail first with new state?
{stillstreaming, Currentstate} ->
NewState = State##mystate{myfun=CurrentState};
我不能打电话gen_server:call(self(),{stream, Tail})
,因为State
需要先更新。而且我不能用新的回复State
,因为模块会发送更多的数据并且尾巴会消失。
有没有办法通过更新再次调用它State
而不用尾部回复并从模块反馈尾部?
更新,代码:
% caller module
case gen_tcp:recv(Socket, 0) of % cannot set Length as it will block untill it is done reading Length number of bytes
{ok, Data} ->
Response = gen_server:call(Pid, {handle_init,Socket,Data}),
case Response of
{ok, continue} ->
pre_loop(Socket, Pid);
{ok, logged_in} ->
{UserId, UserName} = get_user_data(), % ignore it for now.
receiver_loop(UserId, UserName, Socket, Pid);
{stop, Reason} ->
io:format("Error at pre_loop: ~p~n", [Reason]);
_ ->
io:format("Unknown response from call in pre-loop: ~p~n", [Response])
end;
{error, closed} -> % done here as no data was stored in mnesia yet.
gen_server:stop(Pid),
io:format("Client died in pre_loop~n")
end.
和 gen_server 模块:
% gen_server module
handle_call({handle_init, _Socket, Data}, _From, State = #server_state{data_fun = {incomplete, Fun}}) ->
case catch Fun(Data) of
{incomplete, F} ->
NewState = State#server_state{data_fun = {incomplete, F}},
{reply, {ok, continue}, NewState};
{with_tail, Term, Tail} ->
% handle Term login/register only
case handle_input_init(Term, Tail) of
{incomplete, Fn, logged_in} ->
NewState = State#server_state{data_fun = {incomplete, Fn}},
{reply, {ok, logged_in}, NewState};
{incomplete, Fn} ->
NewState = State#server_state{data_fun = {incomplete, Fn}},
{reply, {ok, continue}, NewState};
{stop, malformed_data} ->
{reply, {stop, malformed_data}, State}
end;
_ ->
{reply, {stop, malformed_data}, State}
end;
handle_call(_Message, _From, State = #server_state{}) ->
{reply, {stop , unknown_call}, State}.
handle_input_init(Term, Tail) ->
case handle_term_init(Term) of
{ok, login_passed} ->
io:format("send user a login pass msg"),
handle_tail_init(Tail, logged_in);
{error, login_failed} ->
io:format("send user a login failed error~n"),
handle_tail_init(Tail);
{ok, registration_passed} ->
io:format("send user a registeration passed msg"),
handle_tail_init(Tail);
{error, registration_failed} ->
io:format("send user a registeration failed error"),
handle_tail_init(Tail);
{error, invalidreq} ->
io:format("send user an invalid requst error~n"),
handle_tail_init(Tail)
end.
handle_tail_init(Tail) ->
case catch jsx:decode(Tail, [stream, return_tail, return_maps]) of
{incomplete, F} ->
{incomplete, F};
{with_tail, Term, Tail2} ->
handle_input_init(Term, Tail2);
_ ->
{stop, malformed_data}
end.
handle_tail_init(Tail, logged_in) -> % because it was logged in already, any further requests should be ignored
case catch jsx:decode(Tail, [stream, return_tail, return_maps]) of
{incomplete, F} ->
{incomplete, F, logged_in};
{with_tail, _Term, Tail2} ->
io:format("send user an invalid requst error~n"),
handle_tail_init(Tail2, logged_in);
_ ->
{stop, malformed_data}
end.
handle_term_init(Term) ->
case Term of
#{<<"Login">> := [UserName,Password]} ->
login_user(UserName,Password);
#{<<"Register">> := [UserName,Password]} ->
register_user(UserName,Password);
_ ->
{error, invalidreq}
end.
它按预期工作,但这是我的第一个 Erlang 代码,我很肯定它可以简化为单个递归 handle_call
,保持 OTP 风格,这是我选择 Erlang 的原因。
解决方案
我无法调用 gen_server:call(self(),{stream, Tail}) 因为需要先更新 State。
我真的不明白你想说什么,但如果你的意思是:
我不能递归调用
gen_server:call(self(),{stream, Tail})
,即我不能在handle:call()
递归调用中编写代码handle_call()
。
那么您当然可以将内部的所有数据发送handle:call()
到另一个递归调用自身的函数:
handle_call(...) ->
...
NewState = ....
Result = ...
{FinalResult, FinalState} = helper_func(Result, NewState, Tail)
{reply, FinalResult, FinalState}
helper_func(Result, State, []) ->
{Result, State};
helper_func(Result, State, [Piece|Tail]) ->
...
NewState = ...
NewResult = ...
helper_func(NewResult, NewState, Tail). %% Recursive call here
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