The R13B03 release.OTP_R13B03

1 files changed, 224 insertions, 0 deletions

diff --git a/lib/sasl/src/overload.erl b/lib/sasl/src/overload.erl
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+%%
+%% %CopyrightBegin%
+%% 
+%% Copyright Ericsson AB 1996-2009. All Rights Reserved.
+%% 
+%% The contents of this file are subject to the Erlang Public License,
+%% Version 1.1, (the "License"); you may not use this file except in
+%% compliance with the License. You should have received a copy of the
+%% Erlang Public License along with this software. If not, it can be
+%% retrieved online at http://www.erlang.org/.
+%% 
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights 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 H�gfeldt.
+%%%
+%%% 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() -> gen_server:call(overload, 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) ->
+    gen_server:call(overload, {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() -> gen_server:call(overload, get_overload_info).
+
+%%%-----------------------------------------------------------------
+%%% 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, [])].