这对编辑来说太长了，我把它放在一个新的答案中。
发生超时时收到ok 的原因在于loop() 代码。在第二个接收块中，2000 毫秒后，您返回
紧接在io:format/1 语句之后。
io:format 返回 ok，这就是您在 Returned 变量中得到的内容。您应该使用
更改此代码
loop()->
ok = receive
#'basic.consume_ok'{} -> ok
end,
receive
{#'basic.deliver'{}, #amqp_msg{payload = Payload}} -> {ok,loop2(Payload)}
after 2000 ->
io:format("Server timeout"),
{error,timeout}
end.
使用此代码，您的客户将收到{ok,Value} 或{error,timeout} 并能够做出相应的反应。
但是这个版本还是有问题的：
- 2 秒超时可能太短，您缺少有效答案
- 当您在接收块中使用模式匹配并且不检查每个amqp_channel:call 的结果时，可能会出现许多不同的问题并显示为超时
首先让我们看看超时。对amqp_channel 的 4 次调用可能总共需要超过 2 秒才能成功完成。简单的解决方案是增加超时时间，将after 2000 更改为after 3000 或更多。
但是你会遇到两个问题：
- 您的 gen_server 在此期间一直被阻止，如果它不是专用于单个客户端，它将无法用于
在等待答复时处理任何其他请求。
- 如果您需要将超时时间增加到 5 秒以上，您将遇到另一个超时，由 gen_server 内部管理：请求必须在 5 秒内得到答复。
gen_server 提供了一些接口函数来解决这类问题：'send_request'、'wait_response'和reply。这是一个基本的
gen_server 可以处理 3 种请求：
- stop ... 停止服务器，对更新代码很有用。
- {blocking,Time,Value} 服务器将在 Time ms 结束期间休眠，然后返回 Value。这模拟了你的情况，你可以调整如何
需要很长时间才能得到答案。
- {non_blocking,Time,Value} 服务器会将作业委托给另一个进程并立即返回而无应答（因此
它可用于另一个请求）。新进程将在 Time ms 结束期间休眠，然后使用 gen_server:reply 返回值。
服务器模块实现了几个用户界面：
- 标准的 start()、stop()
- blocking(Time,Value) 使用 gen_server:call 通过请求 {blocking,Time,Value} 调用服务器
- blocking_catch(Time,Value) 与上一个相同，但捕获 gen_server:call 的结果以显示隐藏的超时
- non_blocking(Time,Value,Wait) 使用 gen_server:send_request 使用请求 {non_blocking,Time,Value} 调用服务器并等待等待 ms 最大值的答案
最后它包括2个测试功能
- test([Type,Time,Value,OptionalWait]) 它产生一个进程，该进程将发送一个带有相应参数的类型的请求。答案被发送回调用进程。可以在 shell 中使用 flush() 来检索答案。
- parallel_test ([Type,Time,NbRequests,OptionalWait]) 它使用相应的参数调用 NbRequests 次测试。它收集了所有
答案并使用本地函数 collect(NbRequests,Timeout) 打印出来。
代码如下
-module (server_test).
-behaviour(gen_server).
%% API
-export([start/0,stop/0,blocking/2,blocking_catch/2,non_blocking/3,test/1,parallel_test/1]).
%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-define(SERVER, ?MODULE).
%%%===================================================================
%%% API
%%%===================================================================
start() ->
gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
stop() ->
gen_server:cast(?SERVER, stop).
blocking(Time,Value) ->
gen_server:call(?SERVER, {blocking,Time,Value}).
blocking_catch(Time,Value) ->
catch {ok,gen_server:call(?SERVER, {blocking,Time,Value})}.
non_blocking(Time,Value,Wait) ->
ReqId = gen_server:send_request(?SERVER,{non_blocking,Time,Value}),
gen_server:wait_response(ReqId,Wait).
test([Type,Time,Value]) -> test([Type,Time,Value,5000]);
test([Type,Time,Value,Wait]) ->
Start = erlang:monotonic_time(),
From = self(),
F = fun() ->
R = case Type of
non_blocking -> ?MODULE:Type(Time,Value,Wait);
_ -> ?MODULE:Type(Time,Value)
end,
From ! {request,Type,Time,Value,got_answer,R,after_microsec,erlang:monotonic_time() - Start}
end,
spawn(F).
parallel_test([Type,Time,NbRequests]) -> parallel_test([Type,Time,NbRequests,5000]);
parallel_test([Type,Time,NbRequests,Wait]) ->
case Type of
non_blocking -> [server_test:test([Type,Time,X,Wait]) || X <- lists:seq(1,NbRequests)];
_ -> [server_test:test([Type,Time,X]) || X <- lists:seq(1,NbRequests)]
end,
collect_answers(NbRequests,Time + 1000).
%%%===================================================================
%%% gen_server callbacks
%%%===================================================================
init([]) ->
{ok, #{}}.
handle_call({blocking,Time,Value}, _From, State) ->
timer:sleep(Time),
Reply = {ok,Value},
{reply, Reply, State};
handle_call({non_blocking,Time,Value}, From, State) ->
F = fun() ->
do_answer(From,Time,Value)
end,
spawn(F),
{noreply, State};
handle_call(_Request, _From, State) ->
Reply = ok,
{reply, Reply, State}.
handle_cast(stop, State) ->
{stop,stopped, State};
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(OldVsn, State, _Extra) ->
io:format("changing code replacing version ~p~n",[OldVsn]),
{ok, State}.
%%%===================================================================
%%% Internal functions
%%%===================================================================
do_answer(From,Time,Value) ->
timer:sleep(Time),
gen_server:reply(From, Value).
collect_answers(0,_Timeout) ->
got_all_answers;
collect_answers(NbRequests,Timeout) ->
receive
A -> io:format("~p~n",[A]),
collect_answers(NbRequests - 1, Timeout)
after Timeout ->
missing_answers
end.
shell 中的会话：
44> c(server_test).
{ok,server_test}
45> server_test:start().
{ok,<0.338.0>}
46> server_test:parallel_test([blocking,200,3]).
{request,blocking,200,1,got_answer,{ok,1},after_microsec,207872}
{request,blocking,200,2,got_answer,{ok,2},after_microsec,415743}
{request,blocking,200,3,got_answer,{ok,3},after_microsec,623615}
got_all_answers
47> % 3 blocking requests in parallel, each lasting 200ms, they are executed in sequence but no timemout is reached
47> % All the clients get their answers
47> server_test:parallel_test([blocking,2000,3]).
{request,blocking,2000,1,got_answer,{ok,1},after_microsec,2063358}
{request,blocking,2000,2,got_answer,{ok,2},after_microsec,4127740}
missing_answers
48> % 3 blocking requests in parallel, each lasting 2000ms, they are executed in sequence and the last answer exceeds the gen_server timeout.
48> % The client for this request don't receive answer. The client should also manage its own timeout to handle this case
48> server_test:parallel_test([blocking_catch,2000,3]).
{request,blocking_catch,2000,1,got_answer,{ok,1},after_microsec,2063358}
{request,blocking_catch,2000,2,got_answer,{ok,2},after_microsec,4127740}
{request,blocking_catch,2000,3,got_answer,
{'EXIT',{timeout,{gen_server,call,[server_test,{blocking,2000,3}]}}},
after_microsec,5135355}
got_all_answers
49> % same thing but catching the exception. After 5 seconds the gen_server call throws a timeout exception.
49> % The information can be forwarded to the client
49> server_test:parallel_test([non_blocking,200,3]).
{request,non_blocking,200,1,got_answer,{reply,1},after_microsec,207872}
{request,non_blocking,200,2,got_answer,{reply,2},after_microsec,207872}
{request,non_blocking,200,3,got_answer,{reply,3},after_microsec,207872}
got_all_answers
50> % using non blocking mechanism, we can see that all the requests were managed in parallel
50> server_test:parallel_test([non_blocking,5100,3]).
{request,non_blocking,5100,1,got_answer,timeout,after_microsec,5136379}
{request,non_blocking,5100,2,got_answer,timeout,after_microsec,5136379}
{request,non_blocking,5100,3,got_answer,timeout,after_microsec,5136379}
got_all_answers
51> % if we increase the answer delay above 5000ms, all requests fail in default timeout
51> server_test:parallel_test([non_blocking,5100,3,6000]).
{request,non_blocking,5100,1,got_answer,{reply,1},after_microsec,5231611}
{request,non_blocking,5100,2,got_answer,{reply,2},after_microsec,5231611}
{request,non_blocking,5100,3,got_answer,{reply,3},after_microsec,5231611}
got_all_answers
52> % but thanks to the send_request/wait_response/reply interfaces, the client can adjust the timeout to an accurate value
52> % for each request
请求无法完成的下一个原因是 amqp_channel:call 之一失败。取决于你想做什么，有几个
什么都不做，让崩溃，捕获异常或管理所有情况的可能性。下一个提案使用全局捕获
handle_call({get_account,Timeout}, From, State) ->
F = fun() ->
do_get_account(From,State,Timeout)
end,
spawn(F), % delegate the job to another process and free the server
{noreply, State}; % I don't see any change of State in your code, this should be enough
...
do_get_account(From,State,Timeout) ->
% this block of code asserts all positive return values from amqp_channel calls. it will catch any error
% and return it as {error,...}. If everything goes well it return {ok,Answer}
Reply = try
ok = amqp_channel:call(State, #'exchange.declare'{exchange = <<"get">>, type = <<"topic">>}),
ok = amqp_channel:call(State, #'queue.declare'{queue = <<"get_account">>}),
Binding = #'queue.bind'{exchange = <<"get">>,
routing_key = <<"get.account">>,
queue = <<"get_account">>},
#'queue.bind_ok'{} = amqp_channel:call(State, Binding),
ok = amqp_channel:call(State,#'basic.consume'{queue = <<"get_account">>, no_ack = true}),
{ok,wait_account_reply(Timeout)}
catch
Class:Exception -> {error,Class,Exception}
end,
gen_server:reply(From, Reply).
wait_account_reply(Timeout) ->
receive
% #'basic.consume_ok'{} -> ok % you do not handle this message, ignore it since it will be garbaged when the process die
{#'basic.deliver'{}, #amqp_msg{payload = Payload}} -> extract_account(Payload)
after Timeout->
server_timeout
end.
extract_account(Payload)->
{[{<<"account_id">>, AccountId}]} = jiffy:decode(Payload),
Doc = {[{<<"account_id">>, AccountId}]},
getAccDataDb:create_AccountId_view(), % What is the effect of this function, what is the return value?
case getAccDataDb:getAccountNameDetails(Doc) of
success ->
getAccDataDb:getAccountNameDetails1(Doc);
details_not_matched ->
user_not_exist
end.
客户端应该是这样的：
get_account() ->
ReqId = gen_server:send_request(server_name,{get_account,2000}),
gen_server:wait_response(ReqId,2200).