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small qol update to :telemetry.attach/4 docs #126

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cf38dbd
small qol update to :telemetry.attach/4 docs
ethangunderson Jan 17, 2023
830f38b
raise badarg instead of function clause when a wrong arity function i…
ethangunderson Jan 18, 2023
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19 changes: 13 additions & 6 deletions src/telemetry.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -56,11 +56,11 @@
%%
%% See {@link execute/3} to learn how the handlers are invoked.
%%
%% <b>Note:</b> due to how anonymous functions are implemented in the Erlang VM, it is best to use
%% function captures (i.e. `fun mod:fun/4' in Erlang or `&Mod.fun/4' in Elixir) as event handlers
%% to achieve maximum performance. In other words, avoid using literal anonymous functions
%% (`fun(...) -> ... end' or `fn ... -> ... end') or local function captures (`fun handle_event/4'
%% or `&handle_event/4' ) as event handlers.
%% `function` must be a 4 arity function. Due to how anonymous functions are implemented
%% in the Erlang VM, it is best to use function captures (i.e. `fun mod:fun/4' in Erlang or
%% `&Mod.fun/4' in Elixir) as event handlers to achieve maximum performance. In other words,
%% avoid using literal anonymous functions (`fun(...) -> ... end' or `fn ... -> ... end') or
%% local function captures (`fun handle_event/4' or `&handle_event/4' ) as event handlers.
%%
%% All the handlers are executed by the process dispatching event. If the function fails (raises,
%% exits or throws) then the handler is removed and a failure event is emitted.
Expand Down Expand Up @@ -103,8 +103,9 @@ attach(HandlerId, EventName, Function, Config) ->
EventName :: event_name(),
Function :: handler_function(),
Config :: handler_config().
attach_many(HandlerId, EventNames, Function, Config) when is_function(Function, 4) ->
attach_many(HandlerId, EventNames, Function, Config) ->
assert_event_names(EventNames),
assert_function(Function),
case erlang:fun_info(Function, type) of
{type, external} ->
ok;
Expand Down Expand Up @@ -369,6 +370,12 @@ assert_event_names(List) when is_list(List) ->
assert_event_names(Term) ->
erlang:error(badarg, Term).

-spec assert_function(term()) -> ok.
assert_function(Function) when is_function(Function, 4) ->
ok;
assert_function(Function) ->
erlang:error(badarg, Function).

-spec assert_event_prefix(term()) -> ok.
assert_event_prefix(List) when is_list(List) ->
case lists:all(fun erlang:is_atom/1, List) of
Expand Down
9 changes: 8 additions & 1 deletion test/telemetry_SUITE.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ all() ->
handler_on_multiple_events, remove_all_handler_on_failure,
list_handler_on_many, detach_from_all, old_execute, default_metadata,
off_execute, invoke_successful_span_handlers, invoke_exception_span_handlers,
spans_generate_unique_default_contexts, logs_on_local_function].
spans_generate_unique_default_contexts, logs_on_local_function, badarg_on_wrong_arity_function].

init_per_suite(Config) ->
application:ensure_all_started(telemetry),
Expand Down Expand Up @@ -426,6 +426,13 @@ spans_generate_unique_default_contexts(Config) ->
1000 -> ct:fail(timeout_receive_echo)
end.

badarg_on_wrong_arity_function(Config) ->
HandlerId = ?config(id, Config),
Event = [a, first, event],
HandlerFun = fun ?MODULE:wrong_arity_function/3,

?assertError(badarg, telemetry:attach(HandlerId, Event, HandlerFun, nil)).

logs_on_local_function(Config) ->
HandlerId = ?config(id, Config),
Event = [some, action],
Expand Down