[erlang-questions] gen_server:call/3 and timeout handling

zabrane Mikael <>
Thu Dec 3 11:27:04 CET 2009


Hi Robert !

Applied your try-catch in my code. It works perfectly. Thanks again.

Regards
Zabrane

2009/12/3 Robert Raschke <>

> On Wed, Dec 2, 2009 at 10:48 PM, zabrane Mikael <>wrote:
>
>> When I use the call "gen_server:call/3 (I mean using the timeout option),
>> a timout may occur if the corresponding  "gen_server:handle_call/3" takes
>> take too long.
>> Then, the whole "gen_server" crashes with an error report.
>>
>>
>> What I'd like to achieve is  to "intercept" this "timeout" message in my
>> "gen_server" code and handle
>> it gracefully without stopping my "gen_server" (eg. by sending back a
>> reply
>> with reason = timeout).
>>
>> Is this possible? Is there a best practice for that?
>>
>>
> I think you would need to wrap the call in a try-catch, as the function
> call itself is failing due to the timeout.
>
> For example, using this dummy server:
>
> -module(timeout_test).
> -behaviour(gen_server).
>
> -export([start_link/0, test/0]).
> -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
> code_change/3, terminate/2]).
>
> start_link() -> gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
> test() -> gen_server:call(?MODULE, test, 1000).
>
> init([]) -> {ok, []}.
>
> handle_call(test, _From, State) -> {reply, timer:sleep(1500), State}.
>
> handle_cast(_Request, State) -> {noreply, State}.
> handle_info(_, State) -> {noreply, State}.
> code_change(_Old, State, _Extra) -> {ok, State}.
> terminate(_Reason, _State) -> ok.
>
>
> And in the shell:
>
> Eshell V5.6.5  (abort with ^G)
> 1> c(timeout_test).
> {ok,timeout_test}
> 2> timeout_test:start_link().
> {ok,<0.27047.4>}
> 3> try timeout_test:test() catch Error:Reason -> {Error, Reason} end.
> {exit,{timeout,{gen_server,call,[timeout_test,test,1000]}}}
> 4>
>
> You can obviously also put the try-catch into the function that does the
> gen_server:call and return interesting values depending on the catch.
>
> Hope this gets you in the right direction,
> Robby
>
>


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