%% Copyright (c) 2011-2013 Basho Technologies, Inc. All Rights Reserved.
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%%
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%% This file is provided to you under the Apache License,
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%% Version 2.0 (the "License"); you may not use this file
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%% except in compliance with the License. You may obtain
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%% a copy of the License at
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%%
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%% http://www.apache.org/licenses/LICENSE-2.0
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%%
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%% Unless required by applicable law or agreed to in writing,
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%% software distributed under the License is distributed on an
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%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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%% KIND, either express or implied. See the License for the
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%% specific language governing permissions and limitations
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%% under the License.
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%% @doc A simple gen_event backend used to monitor mailbox size and
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%% switch log messages between synchronous and asynchronous modes.
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%% A gen_event handler is used because a process getting its own mailbox
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%% size doesn't involve getting a lock, and gen_event handlers run in their
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%% parent's process.
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-module(lager_backend_throttle).
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-include("lager.hrl").
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-behaviour(gen_event).
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-export([init/1, handle_call/2, handle_event/2, handle_info/2, terminate/2,
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code_change/3]).
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%%
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%% Allow test code to verify that we're doing the needful.
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-ifdef(TEST).
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-define(ETS_TABLE, async_threshold_test).
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-define(TOGGLE_SYNC(), test_increment(sync_toggled)).
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-define(TOGGLE_ASYNC(), test_increment(async_toggled)).
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-else.
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-define(TOGGLE_SYNC(), true).
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-define(TOGGLE_ASYNC(), true).
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-endif.
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-record(state, {
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sink :: atom(),
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hwm :: non_neg_integer(),
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window_min :: non_neg_integer(),
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async = true :: boolean()
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}).
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init([{sink, Sink}, Hwm, Window]) ->
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lager_config:set({Sink, async}, true),
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{ok, #state{sink=Sink, hwm=Hwm, window_min=Hwm - Window}}.
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handle_call(get_loglevel, State) ->
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{ok, {mask, ?LOG_NONE}, State};
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handle_call({set_loglevel, _Level}, State) ->
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{ok, ok, State};
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handle_call(_Request, State) ->
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{ok, ok, State}.
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handle_event({log, _Message},State) ->
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{message_queue_len, Len} = erlang:process_info(self(), message_queue_len),
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case {Len > State#state.hwm, Len < State#state.window_min, State#state.async} of
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{true, _, true} ->
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%% need to flip to sync mode
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?TOGGLE_SYNC(),
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lager_config:set({State#state.sink, async}, false),
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{ok, State#state{async=false}};
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{_, true, false} ->
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%% need to flip to async mode
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?TOGGLE_ASYNC(),
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lager_config:set({State#state.sink, async}, true),
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{ok, State#state{async=true}};
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_ ->
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%% nothing needs to change
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{ok, State}
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end;
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handle_event(_Event, State) ->
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{ok, State}.
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handle_info(_Info, State) ->
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{ok, State}.
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%% @private
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terminate(_Reason, _State) ->
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ok.
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%% @private
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code_change(_OldVsn, State, _Extra) ->
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{ok, State}.
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-ifdef(TEST).
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test_get(Key) ->
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get_default(ets:lookup(?ETS_TABLE, Key)).
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test_increment(Key) ->
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ets:insert(?ETS_TABLE,
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{Key, test_get(Key) + 1}).
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get_default([]) ->
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0;
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get_default([{_Key, Value}]) ->
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Value.
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-endif.
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