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%%============================================================================== |
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%% Copyright 2016 Erlang Solutions Ltd. |
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%% |
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%% Licensed under the Apache License, Version 2.0 (the "License"); |
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%% you may not use this file except in compliance with the License. |
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%% You may obtain 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, software |
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%% distributed under the License is distributed on an "AS IS" BASIS, |
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%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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%% See the License for the specific language governing permissions and |
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%% limitations under the License. |
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%%============================================================================== |
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-module(shaper). |
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-author('konrad.zemek@erlang-solutions.com'). |
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-export([new/1, update/2]). |
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-record(shaper, { |
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max_rate :: undefined | pos_integer(), |
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tokens = 0 :: non_neg_integer(), |
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last_update = erlang:monotonic_time(millisecond) :: integer() |
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}). |
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-type shaper() :: #shaper{} | none. |
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-export_type([shaper/0]). |
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-spec new(atom()) -> shaper(). |
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new(Name) -> |
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case mongoose_config:lookup_opt([shaper, Name]) of |
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{ok, #{max_rate := MaxRatePerSecond}} -> |
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#shaper{max_rate = MaxRatePerSecond, |
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tokens = MaxRatePerSecond, |
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last_update = erlang:monotonic_time(millisecond)}; |
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{error, not_found} -> none |
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end. |
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%% @doc Update shaper. |
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%% `Delay' is how many milliseconds to wait. |
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-spec update(shaper(), Size :: pos_integer()) -> {shaper(), Delay :: non_neg_integer()}. |
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update(none, _Size) -> |
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{none, 0}; |
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update(#shaper{max_rate = MaxRatePerSecond, |
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tokens = LastAvailableTokens, |
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last_update = LastUpdate}, NowUsed) -> |
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Now = erlang:monotonic_time(millisecond), |
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% How much we might have recovered since last time, in milliseconds arithmetic |
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GrowthPerMillisecond = MaxRatePerSecond / 1000, |
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MilliSecondsSinceLastUpdate = (Now - LastUpdate), |
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PossibleTokenGrowth = round(GrowthPerMillisecond * MilliSecondsSinceLastUpdate), |
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% Available plus recovered cannot grow higher than the actual rate limit |
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ExactlyAvailableNow = min(MaxRatePerSecond, LastAvailableTokens + PossibleTokenGrowth), |
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TokensAvailable = max(0, ExactlyAvailableNow - NowUsed), |
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TokensOverused = max(0, NowUsed - ExactlyAvailableNow), |
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MaybeDelay = round(TokensOverused / GrowthPerMillisecond), |
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{#shaper{max_rate = MaxRatePerSecond, |
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tokens = TokensAvailable, |
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last_update = Now + MaybeDelay}, |
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MaybeDelay}. |