Events 如何在Erlang中使用gen_事件调用?
我正在使用Events 如何在Erlang中使用gen_事件调用?,events,erlang,otp,fsm,Events,Erlang,Otp,Fsm,我正在使用gen\u事件行为,当我试图发出gen\u事件:call时,我得到以下错误: > =CRASH REPORT==== 22-Dec-2019::19:17:43.030000 === crasher: > initial call: gen_event:init_it/6 > pid: <0.215.0> > registered_name: hev > exception exit: {undef,[{fm
gen\u事件
行为,当我试图发出gen\u事件:call
时,我得到以下错误:
> =CRASH REPORT==== 22-Dec-2019::19:17:43.030000 === crasher:
> initial call: gen_event:init_it/6
> pid: <0.215.0>
> registered_name: hev
> exception exit: {undef,[{fm,state,[<0.215.0>],[]},
> {erl_eval,do_apply,6,
> [{file,"erl_eval.erl"},{line,684}]},
> {shell,exprs,7,[{file,"shell.erl"},{line,686}]},
> {shell,eval_exprs,7,
> [{file,"shell.erl"},{line,642}]},
> {shell,eval_loop,3,
> [{file,"shell.erl"},{line,627}]}]}
> in function gen_event:terminate_server/4 (gen_event.erl, line 354)
> ancestors: [<0.212.0>]
> message_queue_len: 1
> messages: [{'EXIT',<0.212.0>,normal}]
> links: []
> dictionary: []
> trap_exit: true
> status: running
> heap_size: 610
> stack_size: 27
> reductions: 279 neighbours:
处理程序
handle_event({append,Elem},State=#state{xs=XS})->
{ok,#state{xs=[Elem|XS]}};
handle_call(state,State})->
{ok,State,State};
handle_call(Event,State)->
{ok,nada_for_you,State}.
p.S我没有发布所有需要的方法(代码更改、终止..等),但它们是存在的
我没有发布所有需要的方法(代码更改、终止..等),但它们是存在的
1) 无论如何,它们是可选的。检查文档中的绿色大注释,例如
2) 至于你的错误信息:
4) 这里有一个基本语法错误:
handle_call(state,State})->
5) 您正在使用错误数量的参数调用两个函数
您需要更加勤奋地发布实际会产生错误的代码
下面是一个使用gen_event
创建计数器的简单示例:
-module(counter).
-behaviour(gen_event).
-compile(export_all).
%% Callback functions:
init(StartingCount) -> % Called by gen_event:add_handler()
State = StartingCount,
{ok, State}.
terminate(_Reason, State) ->
io:format("Terminating state was: ~w~n", [State]).
% Calls to gen_event:notify() cause this function to execute:
handle_event({increase, Change}, State) ->
NewState = State+Change,
{ok, NewState};
handle_event({decrease, Change}, State) ->
NewState = State-Change,
{ok, NewState}.
% Calls to gen_event:call() cause this function to execute:
handle_call(get_count, State) ->
Reply = io_lib:format("Reply from handle_call(): count is ~w~n", [State]),
{ok, Reply, State};
handle_call({increase_and_get_count, Change}, State) ->
NewState = State+Change,
Reply = io_lib:format("Reply from handle_call(): count is ~w~n", [NewState]),
{ok, Reply, NewState}.
%% User interface functions:
start(StartingCount) ->
ServerName = gen_event_counter,
CallbackModule = counter,
{ok, _Pid} = gen_event:start_link({local, ServerName}),
%Name of process running gen_event server is: gen_event_counter
ok = gen_event:add_handler(ServerName, CallbackModule, StartingCount).
%StartingCount is passed to init() callback
stop() ->
ok = gen_event:stop(gen_event_counter),
stopped.
send_request_with_notify(Request) ->
gen_event:notify(gen_event_counter, Request). % returns immediately, does not wait for a reply.
% Request = {increase, 1}, {decrease, 2}, etc.
% Request is passed as first arg to handle_event().
send_request_with_call(Request) ->
Reply = gen_event:call(gen_event_counter, counter, Request), % waits for a reply
% Request is passed as first arg to handle_call()
io:format("send_request_with_call() returned => ~s", [Reply]).
在外壳中:
~/erlang_programs/gen_event$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3 (abort with ^G)
1> c(counter).
counter.erl:3: Warning: export_all flag enabled - all functions will be exported
{ok,counter}
2> counter:start(0).
ok
3> counter:send_request_with_call(get_count).
send_request_with_call() returned => Reply from handle_call(): count is 0
ok
4> counter:send_request_with_notify({increase, 2}).
ok
5> counter:send_request_with_call(get_count).
send_request_with_call() returned => Reply from handle_call(): count is 2
ok
6> counter:send_request_with_call({increase_and_get_count, 5}).
send_request_with_call() returned => Reply from handle_call(): count is 7
ok
7> counter:stop().
Terminating state was: 7
stopped
8>
~/erlang_programs/gen_event$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3 (abort with ^G)
1> c(hev).
hev.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,hev}
2> hev:start().
ok
3> hev:get_state().
{state,[1]}
4> hev:append(45).
ok
hev:handle_event() called
5> hev:get_state().
{state,[45,1]}
6> hev:other_calls().
nada_for_you
7> hev:stop().
stopped
8>
修复代码中的所有错误后:
-module(hev).
-compile(export_all).
-behaviour(gen_event).
-record(state,{
xs=[]
}).
%callbacks
init(no_args)->
{ok, #state{xs=[1]} }.
handle_event({append,Elem}, #state{xs=XS} ) ->
io:format("hev:handle_event() called~n"),
{ok, #state{xs=[Elem|XS]}}.
handle_call(get_state, State)->
Reply = State,
{ok, Reply, State};
handle_call(_Other, State)->
Reply = nada_for_you,
{ok, Reply, State}.
%**API**
start()->
gen_event:start_link({local, ?MODULE}), %Sets the gen_event server name to ?MODULE
% Server Callback Args for
% Name module init()
gen_event:add_handler(?MODULE, ?MODULE, no_args).
%Tells the gen_event server named ?MODULE to look for the callback functions
%in a module also named ?MODULE
append(Elem)->
% Server Request
% Name (matches against 1st arg in handle_event() )
gen_event:notify(?MODULE, {append, Elem}).
get_state()->
% Server Calback Request
% Name module (matches against 1st arg in handle_call() )
gen_event:call(?MODULE, ?MODULE, get_state).
other_calls() ->
gen_event:call(?MODULE, ?MODULE, {set_state, [1, 2, 3]}).
stop() ->
ok = gen_event:stop(?MODULE),
stopped.
在外壳中:
~/erlang_programs/gen_event$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3 (abort with ^G)
1> c(counter).
counter.erl:3: Warning: export_all flag enabled - all functions will be exported
{ok,counter}
2> counter:start(0).
ok
3> counter:send_request_with_call(get_count).
send_request_with_call() returned => Reply from handle_call(): count is 0
ok
4> counter:send_request_with_notify({increase, 2}).
ok
5> counter:send_request_with_call(get_count).
send_request_with_call() returned => Reply from handle_call(): count is 2
ok
6> counter:send_request_with_call({increase_and_get_count, 5}).
send_request_with_call() returned => Reply from handle_call(): count is 7
ok
7> counter:stop().
Terminating state was: 7
stopped
8>
~/erlang_programs/gen_event$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3 (abort with ^G)
1> c(hev).
hev.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,hev}
2> hev:start().
ok
3> hev:get_state().
{state,[1]}
4> hev:append(45).
ok
hev:handle_event() called
5> hev:get_state().
{state,[45,1]}
6> hev:other_calls().
nada_for_you
7> hev:stop().
stopped
8>
请注意,
notify()
会导致使用add\u handler()
添加的所有模块中的handle\u event()
函数执行,而call()
针对特定模块的handle\u call()
函数。乍一看,问题在于gen\u event:call(Pid,state)
。没有导出genu事件:call/2
函数,只有,这意味着您必须显式地将处理程序传递给genu事件:call
。另外请注意,genu event:notify/2
将返回:ok
,无论发生什么情况,这并不意味着呼叫成功。
~/erlang_programs/gen_event$ erl
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V9.3 (abort with ^G)
1> c(hev).
hev.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,hev}
2> hev:start().
ok
3> hev:get_state().
{state,[1]}
4> hev:append(45).
ok
hev:handle_event() called
5> hev:get_state().
{state,[45,1]}
6> hev:other_calls().
nada_for_you
7> hev:stop().
stopped
8>