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-%%
-%% %CopyrightBegin%
-%%
-%% Copyright Ericsson AB 1996-2013. All Rights Reserved.
-%%
-%% Licensed 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.
-%%
-%% %CopyrightEnd%
-%%
--module(overload).
-
--export([start_link/0, request/0, set_config_data/2,
- get_overload_info/0]).
-
--export([init/1, handle_call/3, handle_info/2, terminate/2,
- format_status/2]).
-
-%%%-----------------------------------------------------------------
-%%% This is a rewrite of overload from BS.3, by Peter Högfeldt.
-%%%
-%%% DESCRIPTION
-%%%
-%%% This module implements a server process that keeps record of the
-%%% intensity of calls of the request/0 function, and answers accept or
-%%% reject depending on if the current average intensity is not greater
-%%% than a specified maximum intensity.
-%%%
-%%% The intensity i is calculated according to the formula:
-%%% i(n) = exp(-K*(T(n) - T(n-1)))*i(n-1) + Kappa
-%%% where i(n) is the intensity at event n, Kappa is a constant, and
-%%% T(n) is the time at event n.
-%%%
-%%% The constant Kappa can be thought of as 1 / T, where T is the time
-%%% constant. Kappa is externally referred to as Weight.
-%%%
-%%% We keep track of two intensities: the total call intensity and the
-%%% intensity of accepted calls.
-%%%-----------------------------------------------------------------
-%%% TODO
-%%%
-%%% 3. Hysteresis.
-%%%
-%%%-----------------------------------------------------------------
-
--record(state, {total = 0, accept = 0, max, prev_t = get_now(),
- kappa, call_counts = {0, 0}, alarm = clear}).
-
--define(clear_timeout, 30000).
-
-start_link() ->
- gen_server:start_link({local, overload}, overload, [], []).
-
-init([]) ->
- process_flag(priority, high),
- MaxIntensity = fetch_config_data(overload_max_intensity),
- Kappa = fetch_config_data(overload_weight),
- {ok, #state{max = MaxIntensity, kappa = Kappa}}.
-
-%%-----------------------------------------------------------------
-%% Func: request/0
-%% Purpose: This is a request to proceed, e.g. a request to
-%% establish a call.
-%% Returns: accept | reject
-%%-----------------------------------------------------------------
-request() -> call(request).
-
-%%-----------------------------------------------------------------
-%% Func: set_config_data/2
-%% Purpose: Set configuration data, and reset intensities.
-%% Arguments: MaxIntensity (real > 0), Weight (real > 0).
-%% Returns: ok | {error, What}
-%% This function is for debugging purposes and is therefore not
-%% documented at all.
-%%-----------------------------------------------------------------
-set_config_data(MaxIntensity, Weight) ->
- call({set_config_data, MaxIntensity, Weight}).
-%%-----------------------------------------------------------------
-%% Func: get_overload_info/0
-%% Returns: A list of tagged items: TotalIntensity, AcceptIntensity,
-%% MaxIntensity, Weight, TotalRequests, AcceptedRequests.
-%%-----------------------------------------------------------------
-get_overload_info() -> call(get_overload_info).
-
-%%-----------------------------------------------------------------
-%% call(Request) -> Term
-%%-----------------------------------------------------------------
-call(Req) ->
- gen_server:call(overload, Req, infinity).
-
-%%%-----------------------------------------------------------------
-%%% Callback functions from gen_server
-%%%-----------------------------------------------------------------
-handle_call(request, _From, State) ->
- #state{total = TI, accept = AI, kappa = Kappa, prev_t = PrevT,
- alarm = Alarm} = State,
- {TR, AR} = State#state.call_counts,
- T = get_now(),
- CurI = new_intensity(AI, T, PrevT, Kappa),
- NewTI = new_intensity(TI, T, PrevT, Kappa) + Kappa,
- if
- CurI =< State#state.max ->
- %% Hysteresis: If alarm is set, and current intensity has
- %% fallen below 75% of max intensity, clear alarm.
- NewAlarm = if
- CurI =< 0.75*State#state.max ->
- clear_alarm(Alarm);
- true ->
- Alarm
- end,
- {reply, accept, State#state{call_counts = {TR+1, AR+1},
- prev_t = T, total = NewTI,
- accept = CurI + Kappa,
- alarm = NewAlarm},
- ?clear_timeout};
- true ->
- %% Set alarm if not already set.
- NewAlarm = set_alarm(Alarm),
- {reply, reject,
- State#state{call_counts = {TR+1, AR}, prev_t = T,
- total = NewTI, accept = CurI,
- alarm = NewAlarm},
- ?clear_timeout}
- end;
-handle_call({set_config_data, MaxIntensity, Weight}, _From, _State) ->
- {reply, ok, #state{max = MaxIntensity, kappa = Weight},
- ?clear_timeout};
-handle_call(get_overload_info, _From, State) ->
- #state{max = MI, total = TI, accept = AI, kappa = Kappa,
- prev_t = PrevT, call_counts = {TR, AR}} = State,
- T = get_now(),
- CurI = new_intensity(AI, T, PrevT, Kappa),
- NewTI = new_intensity(TI, T, PrevT, Kappa),
- Reply = [{total_intensity, NewTI}, {accept_intensity, CurI},
- {max_intensity, MI}, {weight, Kappa},
- {total_requests, TR}, {accepted_requests, AR}],
- {reply, Reply, State#state{total = NewTI, accept = CurI},
- ?clear_timeout}.
-
-handle_info(timeout, State) ->
- #state{total = TI, accept = AI, kappa = Kappa, prev_t = PrevT,
- alarm = Alarm} = State,
- T = get_now(),
- CurI = new_intensity(AI, T, PrevT, Kappa),
- NewTI = new_intensity(TI, T, PrevT, Kappa),
- if
- CurI < 0.75* State#state.max ->
- NewAlarm = clear_alarm(Alarm),
- {noreply, State#state{total = NewTI, accept = CurI,
- alarm = NewAlarm}};
-
- true ->
- {noreply, State#state{total = NewTI, accept = CurI},
- ?clear_timeout}
- end;
-
-handle_info(_, State) ->
- {noreply, State, ?clear_timeout}.
-
-terminate(_Reason, _State) ->
- ok.
-
-%%-----------------------------------------------------------------
-%% Internal functions
-%%-----------------------------------------------------------------
-fetch_config_data(Tag) ->
- case application:get_env(sasl, Tag) of
- {ok, Value} -> Value;
- _ -> fetch_default_data(Tag)
- end.
-
-fetch_default_data(overload_max_intensity) -> 0.8;
-fetch_default_data(overload_weight) -> 0.1.
-
-set_alarm(clear) ->
- alarm_handler:set_alarm({overload, []}),
- set;
-set_alarm(Alarm) ->
- Alarm.
-
-clear_alarm(set) ->
- alarm_handler:clear_alarm(overload),
- clear;
-clear_alarm(Alarm) ->
- Alarm.
-
-%%-----------------------------------------------------------------
-%% The catch protects against floating-point exception.
-%%
-new_intensity(I, T, PrevT, K) ->
- Diff = sub(T, PrevT)/1000,
- case catch (I*math:exp(-K*Diff)) of
- {'EXIT', _} -> % Assume zero.
- 0.0;
- Res ->
- Res
- end.
-
-%% Mask equal to 2^27 - 1, used below.
--define(mask27, 16#7ffffff).
-
-%% Returns number of milliseconds in the range [0, 2^27 - 1]. Must have
-%% this since statistics(wall_clock) wraps. Having 2^27 -1 as the max
-%% assures that we always get non-negative integers. 2^27 milliseconds
-%% are approx. 37.28 hours.
-get_now() ->
- element(1, statistics(wall_clock)) band ?mask27.
-
-%% Returns (X - Y) mod 2^27 (which is in the range [0, 2^27 - 1]).
-sub(X, Y) ->
- (X + (bnot Y) + 1) band ?mask27.
-
-format_status(Opt, [PDict, #state{max = MI, total = TI, accept = AI,
- kappa = K,
- call_counts = {TR, AR}}]) ->
- [{data, [{"Total Intensity", TI},
- {"Accept Intensity", AI},
- {"Max Intensity", MI},
- {"Weight", K},
- {"Total requests", TR},
- {"Accepted requests", AR}]} |
- misc_supp:format_pdict(Opt, PDict, [])].