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%% Copyright (c) 2011 Basho Technologies, Inc. All Rights Reserved.
%%
%% This file is provided to you under the Apache License,
%% Version 2.0 (the "License"); you may not use this file
%% except in compliance with the License. You may obtain
%% a copy of the License at
%%
%% http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing,
%% software distributed under the License is distributed on an
%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
%% KIND, either express or implied. See the License for the
%% specific language governing permissions and limitations
%% under the License.
%% @doc A process that does a gen_event:add_sup_handler and attempts to re-add
%% event handlers when they exit.
%% @private
-module(lager_handler_watcher).
-behaviour(gen_server).
-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").
-endif.
%% callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
code_change/3]).
-export([start_link/3, start/3]).
-record(state, {
module,
config,
event
}).
start_link(Event, Module, Config) ->
gen_server:start_link(?MODULE, [Event, Module, Config], []).
start(Event, Module, Config) ->
gen_server:start(?MODULE, [Event, Module, Config], []).
init([Event, Module, Config]) ->
install_handler(Event, Module, Config),
{ok, #state{event=Event, module=Module, config=Config}}.
handle_call(_Call, _From, State) ->
{reply, ok, State}.
handle_cast(_Request, State) ->
{noreply, State}.
handle_info({gen_event_EXIT, Module, normal}, #state{module=Module} = State) ->
{stop, normal, State};
handle_info({gen_event_EXIT, Module, shutdown}, #state{module=Module} = State) ->
{stop, normal, State};
handle_info({gen_event_EXIT, Module, Reason}, #state{module=Module,
config=Config, event=Event} = State) ->
case lager:log(error, self(), "Lager event handler ~p exited with reason ~s",
[Module, error_logger_lager_h:format_reason(Reason)]) of
ok ->
install_handler(Event, Module, Config);
{error, _} ->
%% lager is not working, so installing a handler won't work
ok
end,
{noreply, State};
handle_info(reinstall_handler, #state{module=Module, config=Config, event=Event} = State) ->
install_handler(Event, Module, Config),
{noreply, State};
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
%% internal
install_handler(Event, Module, Config) ->
case gen_event:add_sup_handler(Event, Module, Config) of
ok ->
_ = lager:log(debug, self(), "Lager installed handler ~p into ~p", [Module, Event]),
ok;
Error ->
%% try to reinstall it later
_ = lager:log(error, self(), "Lager failed to install handler ~p into"
" ~p, retrying later : ~p", [Module, Event, Error]),
erlang:send_after(5000, self(), reinstall_handler),
ok
end.
-ifdef(TEST).
from_now(Seconds) ->
{Mega, Secs, Micro} = os:timestamp(),
{Mega, Secs + Seconds, Micro}.
reinstall_on_initial_failure_test_() ->
{timeout, 60000,
[
fun() ->
error_logger:tty(false),
application:load(lager),
application:set_env(lager, handlers, [{lager_test_backend, info}, {lager_crash_backend, [from_now(2), undefined]}]),
application:set_env(lager, error_logger_redirect, false),
application:unset_env(lager, crash_log),
application:start(compiler),
application:start(syntax_tools),
application:start(lager),
try
?assertEqual(1, lager_test_backend:count()),
{_Level, _Time, [_, _, Message]} = lager_test_backend:pop(),
?assertMatch("Lager failed to install handler lager_crash_backend into lager_event, retrying later :"++_, lists:flatten(Message)),
?assertEqual(0, lager_test_backend:count()),
timer:sleep(6000),
?assertEqual(0, lager_test_backend:count()),
?assert(lists:member(lager_crash_backend, gen_event:which_handlers(lager_event)))
after
application:stop(lager),
error_logger:tty(true)
end
end
]
}.
reinstall_on_runtime_failure_test_() ->
{timeout, 60000,
[
fun() ->
error_logger:tty(false),
application:load(lager),
application:set_env(lager, handlers, [{lager_test_backend, info}, {lager_crash_backend, [undefined, from_now(5)]}]),
application:set_env(lager, error_logger_redirect, false),
application:unset_env(lager, crash_log),
application:start(compiler),
application:start(syntax_tools),
application:start(lager),
try
?assertEqual(0, lager_test_backend:count()),
?assert(lists:member(lager_crash_backend, gen_event:which_handlers(lager_event))),
timer:sleep(6000),
?assertEqual(2, lager_test_backend:count()),
{_Level, _Time, [_, _, Message]} = lager_test_backend:pop(),
?assertEqual("Lager event handler lager_crash_backend exited with reason crash", lists:flatten(Message)),
{_Level2, _Time2, [_, _, Message2]} = lager_test_backend:pop(),
?assertMatch("Lager failed to install handler lager_crash_backend into lager_event, retrying later :"++_, lists:flatten(Message2)),
?assertEqual(false, lists:member(lager_crash_backend, gen_event:which_handlers(lager_event)))
after
application:stop(lager),
error_logger:tty(true)
end
end
]
}.
-endif.
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