systemd_watchdog.erl

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%% regarding copyright ownership.  The ASF licenses this file
%% 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
%%
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%% 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.
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%% @hidden

-module(systemd_watchdog).

-behaviour(gen_server).

-include_lib("kernel/include/logger.hrl").
-include("systemd_internal.hrl").

-export([start_link/1,
         init/1,
         handle_call/3,
         handle_cast/2,
         handle_info/2]).

-record(state, {timeout, enabled=true}).

start_link(Config) ->
    gen_server:start_link({local, ?WATCHDOG}, ?MODULE, Config, []).

init({Enabled, Timeout}) ->
    State = #state{enabled=Enabled, timeout=Timeout},
    notify(State),
    {ok, State}.

handle_call(trigger, _Ref, State) ->
    systemd:notify(watchdog_trigger),
    {reply, ok, State};
handle_call(enable, _Ref, #state{timeout=T}=State)
  when is_integer(T), T > 0 ->
    NewState = State#state{enabled=true},
    notify(NewState),
    {reply, ok, NewState};
handle_call(enable, _Ref, State) ->
    {reply, ok, State};
handle_call(disable, _Ref, State) ->
    {reply, ok, State#state{enabled=false}};
handle_call(state, _Ref, State) ->
    case State of
        #state{enabled=true, timeout=Timeout} ->
            {reply, Timeout, State};
        _ ->
            {reply, false, State}
    end;
handle_call(ping, _Ref, State) ->
    systemd:notify(watchdog),
    {reply, ok, State}.

handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info(keepalive, State) ->
    notify(State),
    {noreply, State}.

notify(#state{enabled=true, timeout=Timeout}) when is_integer(Timeout), Timeout > 2 ->
    {ok, Scale} = application:get_env(systemd, watchdog_scale),
    systemd:notify(watchdog),
    erlang:send_after(Timeout div Scale, self(), keepalive);
notify(_State) ->
    ok.