Full Code of klarna/circuit_breaker for AI

Repository: klarna/circuit_breaker
Branch: master
Commit: 840c38e65460
Files: 16
Total size: 53.4 KB

Directory structure:
gitextract_vi90d9g9/

├── .gitignore
├── .travis.yml
├── LICENSE
├── README.md
├── doc/
│   ├── .gitignore
│   └── overview.edoc
├── ebin/
│   └── .gitignore
├── include/
│   └── circuit_breaker.hrl
├── rebar.config
├── src/
│   ├── circuit_breaker.app.src
│   ├── circuit_breaker.erl
│   ├── circuit_breaker_app.erl
│   ├── circuit_breaker_event.erl
│   └── circuit_breaker_sup.erl
└── test/
    ├── circuit_breaker_event_test.erl
    └── circuit_breaker_tests.erl

================================================
FILE CONTENTS
================================================

================================================
FILE: .gitignore
================================================
_build


================================================
FILE: .travis.yml
================================================
sudo: false

language: erlang

# Use the TEST env variable as the test command
script:
 - $TEST

# Special jobs
matrix:

  # Tests to run only with only the top OTP version (latest)
  include:

  # Check dialyzer
  - env: TEST="rebar3 dialyzer"

# Tests to run with every OTP release
env:
  - TEST="rebar3 eunit"

# Which OTP releases to test (keep latest on top)
otp_release:

  # Two latest minor versions of the most recent OTP release
  - 21.0

  # Last minor version of older OTP releases
  - 20.3
  - 19.3
  - 18.3

# Keep rebar cache (for PLT)
cache:
  directories:
  - "$HOME/.cache/rebar3"


================================================
FILE: LICENSE
================================================
Apache License
                           Version 2.0, January 2004
                        http://www.apache.org/licenses/

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================================================
FILE: README.md
================================================
[![Build Status](https://travis-ci.org/klarna/circuit_breaker.svg?branch=master)](https://travis-ci.org/klarna/circuit_breaker)

Generic circuit breaker that can be used to break any service that
isn't fully functional. A service can be manually blocked/cleared as well.

See doc/overview.edoc for more info.

Building
========

    rebar3 compile
    rebar3 doc
    rebar3 eunit

Using
=====

```erlang
%% Circuit-breaking
call(State, SomeId) ->
    circuit_breaker:call(
        % service identifier for the circuit
        {myservice, SomeId},

        % function being monitored
        fun() -> some_call(State) end,

        % call timeout
        timer:minutes(1),

        % reset fun, just returns true
        fun() -> true end,

        % timeout before reset in case of break
        timer:minutes(5),

        %% Options
        [
            % Number of errors tolerated per unit of time.
            {n_error, 3},
            {time_error, timer:minutes(30)},

            %% number of calls returning 'timeout' tolerated in a given
            %% period of time.
            {n_timeout, 3},
            % interval to happen
            {time_timeout, timer:minutes(30)},

            %% number of calls not responding in due time tolerated, and
            %% the time interval for the N failures to happen
            {n_call_timeout, 3},
            {time_call_timeout, timer:minutes(25)},

            %% When failing, the {'EXIT', Reason} tuple will be returned from
            %% the call. This list of `Reason's allows to avoid counting specific
            %% errors towards thresholds that can break a circuit.
            {ignore_errors, []}
        ]
    ).
```


================================================
FILE: doc/.gitignore
================================================
edoc-info
erlang.png
stylesheet.css
*.html


================================================
FILE: doc/overview.edoc
================================================
@copyright 2012 Klarna AB
@title Circuit breaker
@doc Circuit breaker

== General ==

Generic circuit breaker that can be used to break any service that
isn't fully functional. A service can be manually blocked/cleared as well.
The service will be executed in a spawned process that will continue
execution even after a specified call timeout in order to be able
to complete a request even if a response is not sent to the client.
NOTE: It's important that the service can store it's result even
if the result is not returned to the client.

Information regarding current services under circuit breaker
control can be displayed by: circuit_breaker:info/0.

The circuit breaker generates an error event if a service is
automatically blocked due to too many errors/timeouts.
An info event is sent when the service is automatically cleared again.

If several services are used to provide functionallity it's
outside the scope of this server to take care (e.g. send
a critical event) in the case that all used services are
blocked.

The heuristics/thresholds are configurable per service.

@end

================================================
FILE: ebin/.gitignore
================================================
*.app
*.beam


================================================
FILE: include/circuit_breaker.hrl
================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Copyright 2012 Klarna AB
%%%
%%% 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.
%%%
%%% @doc Circuit breaker
%%% @copyright 2012 Klarna AB
%%% @end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%_* Defines ==========================================================
%% #circuit_breaker.flags
-define(CIRCUIT_BREAKER_OK,           0).
-define(CIRCUIT_BREAKER_WARNING,      (1 bsl 0)).
-define(CIRCUIT_BREAKER_BLOCKED,      (1 bsl 1)).
-define(CIRCUIT_BREAKER_CALL_TIMEOUT, (1 bsl 2)).
-define(CIRCUIT_BREAKER_TIMEOUT,      (1 bsl 3)).
-define(CIRCUIT_BREAKER_ERROR,        (1 bsl 4)).

%% Events
-define(manually_blocked,      manually_blocked).
-define(manually_deblocked,    manually_deblocked).
-define(manually_cleared,      manually_cleared).
-define(automatically_blocked, automatically_blocked).
-define(automatically_cleared, automatically_cleared).
-define(error,                 error).
-define(timeout,               timeout).
-define(call_timeout,          call_timeout).
-define(call_dropped,          call_dropped).
-define(ok_time_metric,        ok_time_metric).

%%%_* Emacs ============================================================
%%% Local Variables:
%%% allout-layout: t
%%% erlang-indent-level: 2
%%% End:


================================================
FILE: rebar.config
================================================
{erl_opts,
 [ debug_info
 , warn_export_vars
 , warn_unused_import
 ]}.

{dialyzer,
 [ {warnings,
    [ unmatched_returns
    , underspecs
    ]}
 , {base_plt_apps,
    [ erts
    , kernel
    , stdlib
    ]}
 ]}.


================================================
FILE: src/circuit_breaker.app.src
================================================
%%-*- mode: erlang -*-
{application, circuit_breaker, [ {description, "Circuit breaker"}
                               , {vsn,          git}
                               , {modules,      []}
                               , {registered,   [ circuit_breaker_sup
                                                ]}
                               , {applications, [ kernel
                                                , stdlib
                                                ]}
                               , {mod,          {circuit_breaker_app, []}}
                               ]}.


================================================
FILE: src/circuit_breaker.erl
================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Copyright 2012 Klarna AB
%%%
%%% 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.
%%%
%%% @doc Circuit breaker
%%%
%%% Generic circuit breaker that can be used to break any service that
%%% isn't fully functional. A service can be manually blocked/cleared as well.
%%% The service will be executed in a spawned process that will continue
%%% execution even after a specified call timeout in order to be able
%%% to complete a request even if a response is not sent to the client.
%%% NOTE: It's important that the service can store it's result even
%%% if the result is not returned to the client.
%%%
%%% Information regarding current services under circuit breaker
%%% control can be displayed by: circuit_breaker:info/0.
%%%
%%% The circuit breaker generates an error event if a service is
%%% automatically blocked due to too many errors/timeouts.
%%% An info event is sent when the service is automatically cleared again.
%%%
%%% If several services are used to provide functionallity it's
%%% outside the scope of this server to take care (e.g. send
%%% a critical event) in the case that all used services are
%%% blocked.
%%%
%%% The heuristics/thresholds are configurable per service.
%%%
%%% @copyright 2012 Klarna AB
%%% @end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%_* Module declaration ===============================================
-module(circuit_breaker).

%%%_* Behaviour ========================================================
-behaviour(gen_server).

%%%_* Exports ==========================================================
%% API
-export([ start_link/0
        , call/2
        , call/5
        , call/6
        , clear/1
        , block/1
        , deblock/1
        , disabled/1
        , blocked/1
        , info/0
        , info_to_text/0
        ]).

-export([ ok/1
        , error/2
        , error/4
        , error/5
        , call_timeout/2
        , call_timeout/4
        , call_timeout/5
        , timeout/1
        , timeout/3
        , timeout/4
        ]).

%% Gen server callbacks
-export([ init/1
        , handle_call/3
        , handle_cast/2
        , handle_info/2
        , terminate/2
        , code_change/3
        ]).

%%%_* Includes =========================================================
-include("circuit_breaker.hrl").

-define(bit_clr(Fs,F), ((Fs) band (bnot (F)))).
-define(bit_set(Fs,F), ((Fs) bor (F))).
-define(bit_is_set(Fs, F),       ((Fs) band (F) =/= 0)).
-define(bit_set_rec(Rec, Flag),	Rec{flags = ?bit_set(Rec.flags, Flag)}).


%%%_* Records ==========================================================
-record(state, {}).
-record(circuit_breaker,
        { service                            % Term, e.g. {IP|Host, Port}
        , flags        = ?CIRCUIT_BREAKER_OK % Status, ?CIRCUIT_BREAKER_*
        , timeout      = 0                   % {N, non_neg_integer()} | 0
        , call_timeout = 0                   % {N, non_neg_integer()} | 0
        , error        = 0                   % {N, non_neg_integer()} | 0
        , reset_fun                          % Fun to check for up status
        , ref                                % Timer reference
        }).

%%%_* Defines ==========================================================
-define(SERVER,            ?MODULE).
-define(TABLE,             ?MODULE).
-define(CALL_TIMEOUT,      10 * 1000).      % 10 seconds
-define(RESET_TIMEOUT,     10 * 60 * 1000). % 10 minutes
-define(RESET_FUN,         fun() -> true end).
-define(N_ERROR,           10).
-define(N_TIMEOUT,         10).
-define(N_CALL_TIMEOUT,    10).
-define(TIME_ERROR,        60 * 1000).     % 1 minute
-define(TIME_TIMEOUT,      60 * 1000).     % 1 minute
-define(TIME_CALL_TIMEOUT, 5 * 60 * 1000). % 5 minutes
-define(IGNORE_ERRORS,     [no_hit, not_found]).
-define(THRESHOLDS,        [ {n_error,           ?N_ERROR}
                           , {n_timeout,         ?N_TIMEOUT}
                           , {n_call_timeout,    ?N_CALL_TIMEOUT}
                           , {time_error,        ?TIME_ERROR}
                           , {time_timeout,      ?TIME_TIMEOUT}
                           , {time_call_timeout, ?TIME_CALL_TIMEOUT}
                           , {ignore_errors,     ?IGNORE_ERRORS}
                           ]).

-type event_type() :: automatically_blocked |
                      automatically_cleared |
                      call_dropped          |
                      call_timeout          |
                      error                 |
                      manually_blocked      |
                      manually_cleared      |
                      manually_deblocked    |
                      ok_time_metric        |
                      timeout.

-type event_info() :: proplists:proplist() | #circuit_breaker{}.

-export_type([ event_type/0
             , event_info/0
             ]).

%%%_* API ==============================================================
-spec start_link() -> {ok, Pid::pid()} | ignore | {error, Reason::term()}.
%% @doc Start circuit_breaker.
%% @end
start_link() -> gen_server:start_link({local, ?SERVER}, ?SERVER, [], []).

-spec call(Service::term(), CallFun::function()) -> term().
%% @doc Call Service with default parameters.
%% @end
call(Service, CallFun) ->
  call(Service, CallFun, ?CALL_TIMEOUT, ?RESET_FUN, ?RESET_TIMEOUT).

-spec call(Service::term(), CallFun::function(),
           CallTimeout::integer(), ResetFun::function(),
           ResetTimeout::integer()) -> term().
%% @doc Call Service with custom parameters.
%% @end
call(Service, CallFun, CallTimeout, ResetFun, ResetTimeout) ->
  call(Service, CallFun, CallTimeout, ResetFun, ResetTimeout, ?THRESHOLDS).

-spec call(Service::term(), CallFun::function(),
           CallTimeout::integer(), ResetFun::function(),
           ResetTimeout::integer(), Thresholds::list()) -> term().
%% @doc Call Service with custom parameters.
%% @end
call(Service, CallFun, CallTimeout, ResetFun, ResetTimeout, Thresholds) ->
  case read(Service) of
    R when (R#circuit_breaker.flags > ?CIRCUIT_BREAKER_WARNING) ->
      event(?call_dropped, R),
      {error, {circuit_breaker, R#circuit_breaker.flags}};
    _ -> do_call(Service, CallFun, CallTimeout, ResetFun,
                 ResetTimeout, Thresholds)
  end.

-spec block(Service::term()) -> ok | {error, undefined}.
%% @doc Block Service.
%% @end
block(Service) ->
  case try_read(Service) of
    {ok, _} -> change_status(Service, block);
    false   -> {error, undefined}
  end.

-spec deblock(Service::term()) -> ok | {error, undefined}.
%% @doc Deblock Service.
%% @end
deblock(Service) ->
  case try_read(Service) of
    {ok, _} -> change_status(Service, deblock);
    false   -> {error, undefined}
  end.

-spec blocked(Service::term()) -> boolean().
%% @doc Check if Service is manually blocked.
%% @end
blocked(Service) ->
  case try_read(Service) of
    {ok, R} when ?bit_is_set(R#circuit_breaker.flags,
                             ?CIRCUIT_BREAKER_BLOCKED) -> true;
    _                                                  -> false
  end.

-spec disabled(Service::term()) -> boolean().
%% @doc Check if Service is disabled.
%% @end
disabled(Service) ->
  case try_read(Service) of
    {ok, R} -> R#circuit_breaker.flags >= ?CIRCUIT_BREAKER_BLOCKED;
    false   -> false
  end.

-spec clear(Service::term()) -> ok | {error, undefined}.
%% @doc Clear Service (except for manually blocked services).
%% @end
clear(Service) ->
  case try_read(Service) of
    {ok, _} -> change_status(Service, clear);
    false   -> {error, undefined}
  end.

-spec info() -> ok.
%% @doc Print information regarding services.
%% @end
info() ->
  Text = info_to_text(),
  io:put_chars(Text).

-spec info_to_text() -> io_lib:chars().
%% @doc Print information regarding services.
%% @end
info_to_text() ->
  Header  = format("Service", "Status", "Error", "Timeout", "CallTimeout"),
  Split   = format(dup(31, $-), dup(15, $-), dup(8, $-), dup(8, $-), dup(8, $-)),
  Entries = ets:foldl(fun do_info/2, [], ?TABLE),
  [Header, Split, Entries].

%%%_* Gen server callbacks =============================================
%% @hidden
init([]) ->
  ?TABLE = ets:new(?TABLE, [named_table, {keypos, #circuit_breaker.service}]),
  {ok, #state{}}.

%% @hidden
handle_call({init, Service}, _From, State) ->
  do_init(Service),
  {reply, ok, State};
handle_call({change_status, Service, What}, _From, State) ->
  do_change_status(Service, What),
  {reply, ok, State}.

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

%% @hidden
handle_info({reset, Service, ResetTimeout}, State) ->
  reset_service(Service, ResetTimeout),
  {noreply, State};

%% @hidden
handle_info(_Info, State) -> {noreply, State}.

%% @hidden
terminate(_Reason, _State) -> ok.

%% @hidden
code_change(_OldVsn, State, _Extra) -> {ok, State}.

%%%_* Internal =========================================================

-dialyzer({no_fail_call, do_call/6}).

do_call(Service, CallFun, CallTimeout, ResetFun, ResetTimeout, Thresholds) ->
  Self   = self(),
  Pid    = proc_lib:spawn(fun() -> called(Self, preserve_exception(CallFun, Service), Service) end),
  MonRef = erlang:monitor(process, Pid),
  receive
    {Pid, Result, Service} ->
      erlang:demonitor(MonRef, [flush]),
      handle_result({got, Result}, Service, ResetFun, ResetTimeout, Thresholds);
    {'DOWN', MonRef, process, Pid, Reason} ->
      handle_result({'EXIT', Reason}, Service, ResetFun,
                    ResetTimeout, Thresholds)
  after CallTimeout ->
      %% Let CallFun/0 continue in order to finish work,
      %% but return to client now.
      Pid ! {Self, call_timeout},
      erlang:demonitor(MonRef, [flush]),
      handle_result({error, call_timeout, Pid}, Service, ResetFun,
                    ResetTimeout, Thresholds)
  end.

preserve_exception(CallFun, Service) ->
  try
    Start = os:timestamp(),
    Res = CallFun(),
    End = os:timestamp(),
    TimeTaken = timer:now_diff(End, Start),
    event(?ok_time_metric, Service, [{time, TimeTaken}]),
    Res
  catch
    Class:Reason:Stacktrace ->
      exit({raise, Class, Reason, Stacktrace})
  end.

called(Parent, Result, Service) ->
  receive
    {Parent, call_timeout} -> exit(normal) % Call did timeout, no return
  after 0 -> Parent ! {self(), Result, Service}
  end.

handle_result({got, Result}, Service, ResetFun, ResetTimeout, Thresholds) ->
  case Result of
    {error, timeout}                         ->
      timeout(Service, ResetFun, ResetTimeout, Thresholds);
    Result when element(1, Result) =:= error ->
      error(Service, Result, ResetFun, ResetTimeout, Thresholds);
    _ -> ok(Service)
  end,
  Result;
handle_result({error, call_timeout, Pid}, Service, ResetFun,
              ResetTimeout, Thresholds) ->
  call_timeout(Pid, Service, ResetFun, ResetTimeout, Thresholds),
  {error, timeout};
handle_result({'EXIT', {raise, Class, Reason, Stacktrace}}, Service, ResetFun,
              ResetTimeout, Thresholds) ->
  error(Service, {'EXIT', Reason}, ResetFun, ResetTimeout, Thresholds),
  %% Keep behavior as if CallFun/0 was executed in same process context.
  erlang:raise(Class, Reason, Stacktrace).

error(Service, Error) ->
  error(Service, Error, ?RESET_FUN, ?RESET_TIMEOUT).

error(Service, Error, ResetFun, ResetTimeout) ->
  error(Service, Error, ResetFun, ResetTimeout, ?THRESHOLDS).

error(Service, {_, Reason} = Error, ResetFun, ResetTimeout, Thresholds) ->
  case lists:member(Reason, ignore_errors(Thresholds)) of
    true  -> ok(Service);
    false ->
      event(error, Service, [{error, Error}]),
      change_status(Service, {error, ResetFun, ResetTimeout, Thresholds})
  end.

call_timeout(Pid, Service) ->
  call_timeout(Pid, Service, ?RESET_FUN, ?RESET_TIMEOUT).

call_timeout(Pid, Service, ResetFun, ResetTimeout) ->
  call_timeout(Pid, Service, ResetFun, ResetTimeout, ?THRESHOLDS).

call_timeout(Pid, Service, ResetFun, ResetTimeout, Thresholds) ->
  event(call_timeout, Service, [{error, {call_timeout, Pid}}]),
  change_status(Service, {call_timeout, ResetFun, ResetTimeout, Thresholds}).

timeout(Service) ->
  timeout(Service, ?RESET_FUN, ?RESET_TIMEOUT).

timeout(Service, ResetFun, ResetTimeout) ->
  timeout(Service, ResetFun, ResetTimeout, ?THRESHOLDS).

timeout(Service, ResetFun, ResetTimeout, Thresholds) ->
  event(timeout, Service, [{error, timeout}]),
  change_status(Service, {timeout, ResetFun, ResetTimeout, Thresholds}).

ok(Service) ->
  case try_read(Service) of
    {ok, R} when R#circuit_breaker.flags =/= ?CIRCUIT_BREAKER_OK ->
      change_status(Service, ok);
    {ok, _R} -> ok;
    false    -> init_circuit_breaker(Service)
  end.

init_circuit_breaker(Service) ->
  gen_server:call(?SERVER, {init, Service}, infinity).

change_status(Service, What) ->
  gen_server:call(?SERVER, {change_status, Service, What}, infinity).

do_info(R, Acc) ->
  Service           = io_lib:format("~p", [R#circuit_breaker.service]),
  Status            = fmt_flags(R#circuit_breaker.flags),
  {Errors, _}       = get_data(R, error),
  {Timeouts, _}     = get_data(R, timeout),
  {CallTimeouts, _} = get_data(R, call_timeout),
  Formatted         = format(Service, Status, integer_to_list(Errors),
                             integer_to_list(Timeouts), integer_to_list(CallTimeouts)),
  [Formatted | Acc].

fmt_flags(0) -> [pif(?CIRCUIT_BREAKER_OK)];
fmt_flags(F) -> lists:flatten(string:join(fmt_flags(0, F, []), ", ")).

fmt_flags(Pos, Flags, Acc) when Flags < (1 bsl Pos) ->
  lists:reverse(Acc);
fmt_flags(Pos, Flags, Acc) when ?bit_is_set(Flags, (1 bsl Pos)) ->
  fmt_flags(Pos + 1, Flags, [pif(1 bsl Pos)|Acc]);
fmt_flags(Pos, Flags, Acc) ->
  fmt_flags(Pos + 1, Flags, Acc).

pif(?CIRCUIT_BREAKER_OK)           -> "OK";
pif(?CIRCUIT_BREAKER_WARNING)      -> "WARNING";
pif(?CIRCUIT_BREAKER_BLOCKED)      -> "BLOCKED";
pif(?CIRCUIT_BREAKER_CALL_TIMEOUT) -> "CALL TIMEOUT";
pif(?CIRCUIT_BREAKER_TIMEOUT)      -> "TIMEOUT";
pif(?CIRCUIT_BREAKER_ERROR)        -> "ERROR".

dup(N, Char) -> lists:duplicate(N, Char).

format(A1, A2, A3, A4, A5) ->
  io_lib:format("~-31s ~-15s ~-8s ~-8s ~-8s~n", [A1, A2, A3, A4, A5]).

do_init(Service) ->
  case exists(Service) of
    false -> write(#circuit_breaker{service = Service});
    true  -> ok
  end.

do_change_status(Service, What) ->
  do_change_status(read(Service), Service, What).

%% What = {error, ResetFun, ResetTimeout, Thresholds} |
%%        {call_timeout, ResetFun, ResetTimeout, Thresholds} |
%%        {timeout, ResetFun, ResetTimeout, Thresholds} |
%%        ok |
%%        block |
%%        deblock |
%%        clear
do_change_status(R, Service, {Type, ResetFun, ResetTimeout, Thresholds}) ->
  fault_status(R, Service, Type, ResetFun, ResetTimeout, Thresholds);
do_change_status(R, _Service, ok) ->
  decrease_counter(R);
do_change_status(R0, _Service, block) ->
  %% Manually blocked
  event(manually_blocked, R0),
  R = maybe_cancel_timer(R0),
  write(?bit_set_rec(R#circuit_breaker, ?CIRCUIT_BREAKER_BLOCKED));
do_change_status(R0, Service, deblock) ->
  %% Manually deblocked; create new default #circuit_breaker{}.
  event(manually_deblocked, R0),
  _R = maybe_cancel_timer(R0),
  write(#circuit_breaker{service = Service});
do_change_status(R0, Service, clear) ->
  %% Manually cleared errors; do not clear CIRCUIT_BREAKER_BLOCKED
  event(manually_cleared, R0),
  R = maybe_cancel_timer(R0),
  Flags =
    if
      ?bit_is_set(R#circuit_breaker.flags,
                  ?CIRCUIT_BREAKER_BLOCKED) -> ?CIRCUIT_BREAKER_BLOCKED;
      true                                  -> ?CIRCUIT_BREAKER_OK
    end,
  write(#circuit_breaker{ service = Service
                        , flags   = Flags
                        }).

gnow() ->
  calendar:datetime_to_gregorian_seconds(calendar:local_time()).

fault_status(R0, _Service, Type, ResetFun, ResetTimeout, Thresholds) ->
  Now           = gnow(),
  {N, LastNow}  = get_data(R0, Type),
  NThreshold    = n_threshold(Thresholds, Type),
  TimeThreshold = time_threshold(Thresholds, Type),
  if
    N + 1 =:= NThreshold,
    Now - LastNow < TimeThreshold        ->
      event(automatically_blocked, R0, [{error, Type}]),
      Flag  = flag(Type),
      R1    = maybe_cancel_timer(R0),
      R2    = set_data(R1, Type, {N + 1, Now}),
      R     = start_timer(R2, ResetTimeout),
      Flags = ?bit_clr(R#circuit_breaker.flags, ?CIRCUIT_BREAKER_WARNING),
      write(R#circuit_breaker{ flags     = ?bit_set(Flags, Flag)
                             , reset_fun = ResetFun
                             });
    Now - LastNow < TimeThreshold, N > 0 ->
      write(set_data(R0, Type, {N + 1, Now}));
    true                                 ->
      R = set_data(R0, Type, {1, Now}),
      write(R#circuit_breaker{flags = ?bit_set(R#circuit_breaker.flags,
                                               ?CIRCUIT_BREAKER_WARNING)})
  end.

%% An ok request; decrease a counter in "severity" order.
decrease_counter(R0) ->
  Types = [error, timeout, call_timeout],
  case decrease_counter(Types, R0, false, 1) of
    {WarnP, R} when WarnP =:= false ->
      write(R#circuit_breaker{flags = ?bit_clr(R#circuit_breaker.flags,
                                               ?CIRCUIT_BREAKER_WARNING)});
    {_WarnP, R} -> write(R)
  end.

decrease_counter([Type|Types], R, WarnP, M) when M > 0   ->
  case get_data(R, Type) of
    {0, _} -> decrease_counter(Types, R, WarnP, M);
    {1, _} -> decrease_counter(Types, set_data(R, Type, 0), WarnP, M - 1);
    {N, T} -> decrease_counter(Types,
                               set_data(R, Type, {N - 1, T}), true, M - 1)
  end;
decrease_counter([Type|Types], R, WarnP, M) when M =:= 0 ->
  case get_data(R, Type) of
    {0, _} -> decrease_counter(Types, R, WarnP, M);
    _      -> decrease_counter(Types, R, true, M)
  end;
decrease_counter([], R, WarnP, _M)                       ->
  {WarnP, R}.

reset_service(Service, ResetTimeout) ->
  R = read(Service),
  case catch (R#circuit_breaker.reset_fun)() of
    true when ?bit_is_set(R#circuit_breaker.flags,
                          ?CIRCUIT_BREAKER_BLOCKED) ->
      write(#circuit_breaker{ service = Service
                            , flags   = ?CIRCUIT_BREAKER_BLOCKED
                            });
    true -> event(automatically_cleared, R),
            write(#circuit_breaker{service = Service});
    _    -> write(start_timer(R, ResetTimeout))
  end.

%%%_* Setters/getters --------------------------------------------------
%% Set/get fault data (error, timeout and call_timeout)
get_data(R, Type) ->
  case do_get_data(R, Type) of
    0    -> {0, gnow()};
    Data -> Data
  end.

do_get_data(R, error)           -> R#circuit_breaker.error;
do_get_data(R, timeout)         -> R#circuit_breaker.timeout;
do_get_data(R, call_timeout)    -> R#circuit_breaker.call_timeout.

set_data(R, error, Data)        -> R#circuit_breaker{error = Data};
set_data(R, timeout, Data)      -> R#circuit_breaker{timeout = Data};
set_data(R, call_timeout, Data) -> R#circuit_breaker{call_timeout = Data}.

n_threshold(L, error)        ->
  proplists:get_value(n_error, L, ?N_ERROR);
n_threshold(L, timeout)      ->
  proplists:get_value(n_timeout, L, ?N_TIMEOUT);
n_threshold(L, call_timeout) ->
  proplists:get_value(n_call_timeout, L, ?N_CALL_TIMEOUT).

time_threshold(L, error)        ->
  proplists:get_value(time_error, L, ?TIME_ERROR);
time_threshold(L, timeout)      ->
  proplists:get_value(time_timeout, L, ?TIME_TIMEOUT);
time_threshold(L, call_timeout) ->
  proplists:get_value(time_call_timeout, L, ?TIME_CALL_TIMEOUT).

ignore_errors(L) -> proplists:get_value(ignore_errors, L, ?IGNORE_ERRORS).

flag(error)        -> ?CIRCUIT_BREAKER_ERROR;
flag(timeout)      -> ?CIRCUIT_BREAKER_TIMEOUT;
flag(call_timeout) -> ?CIRCUIT_BREAKER_CALL_TIMEOUT.

%%%_* Timer ------------------------------------------------------------
%% Clear timer if existing
maybe_cancel_timer(R) when R#circuit_breaker.ref =/= undefined ->
  _ = timer:cancel(R#circuit_breaker.ref),
  flush_reset(R),
  R#circuit_breaker{ref = undefined};
maybe_cancel_timer(R) -> R.

flush_reset(R) ->
  receive
    {reset, Service, _ResetTimeout}
      when Service =:= R#circuit_breaker.service -> ok
  after 0 -> ok
  end.

start_timer(R, ResetTimeout) ->
  {ok, Ref} =
    timer:send_after(ResetTimeout, self(),
                     {reset, R#circuit_breaker.service, ResetTimeout}),
  R#circuit_breaker{ref = Ref}.

%%%_* ETS operations ---------------------------------------------------
read(Service) ->
  case ets:lookup(?TABLE, Service) of
    [R] -> R;
    []  -> #circuit_breaker{service = Service}
  end.

try_read(Service) ->
  case ets:lookup(?TABLE, Service) of
    [R] -> {ok, R};
    []  -> false
  end.

exists(Service) -> ets:lookup(?TABLE, Service) =/= [].

write(#circuit_breaker{} = R) -> ets:insert(?TABLE, R).

%%%_* Event ------------------------------------------------------------
-spec event(event_type(), event_info(), proplists:proplist()) -> any().
event(Type, #circuit_breaker{} = R, Info) when is_list(Info) ->
  event(Type, lists:append(Info, to_proplist(R)));
event(Type, Service, Info) when is_list(Info)                ->
  event(Type, read(Service), Info).

-spec event(event_type(), event_info()) -> any().
event(Type, #circuit_breaker{} = R)   -> event(Type, to_proplist(R));
event(Type, Info) when is_list(Info)  ->
  case application:get_env(circuit_breaker, event_handler) of
    {ok, Module} when is_atom(Module) ->
      Module:handle(Type, Info);
    _ ->
      ok
  end.

to_proplist(#circuit_breaker{ service      = Service
                            , flags        = Flags
                            , timeout      = NTimeout
                            , call_timeout = NCallTimeout
                            , error        = NError
                            }) ->
  [ {service, Service}
  , {flags, Flags}
  , {n_timeout, NTimeout}
  , {n_call_timeout, NCallTimeout}
  , {n_error, NError}
  ].

%%%_* Emacs ============================================================
%%% Local Variables:
%%% allout-layout: t
%%% erlang-indent-level: 2
%%% End:


================================================
FILE: src/circuit_breaker_app.erl
================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Copyright 2012 Klarna AB
%%%
%%% 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.
%%%
%%% @doc Circuit breaker application
%%% @copyright 2012 Klarna AB
%%% @end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%_* Module declaration ===============================================
-module(circuit_breaker_app).

%%%_* Behaviour ========================================================
-behaviour(application).

%%%_* Exports ==========================================================
%% Application callbacks
-export([ start/2
        , stop/1
        ]).

%%%_* Application callbacks ============================================
-spec start(StartType::normal | {takeover, node()} | {failover, node()},
            StartArgs::term()) ->
               {ok, Pid::pid()}
             | {error, Reason::term()}.
%% @doc This function is called whenever an application is started using
%% application:start/1,2, and should start the processes of the
%% application. If the application is structured according to the OTP
%% design principles as a supervision tree, this means starting the top
%% supervisor of the tree.
%% @end
start(_StartType, _StartArgs) -> circuit_breaker_sup:start_link().

-spec stop(State::term()) -> ok.
%% @doc This function is called whenever an application has stopped. It is
%% intended to be the opposite of Module:start/2 and should do any
%% necessary cleaning up.
%% @end
stop(_State) -> ok.

%%%_* Emacs ============================================================
%%% Local Variables:
%%% allout-layout: t
%%% erlang-indent-level: 2
%%% End:


================================================
FILE: src/circuit_breaker_event.erl
================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Copyright 2012 Klarna AB
%%%
%%% 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.
%%%
%%% @doc Circuit breaker event behaviour
%%%
%%% Handles events passed from the circuit breaker.
%%%
%%% @copyright 2012 Klarna AB
%%% @end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%_* Module declaration ===============================================
-module(circuit_breaker_event).

%%%_* Exports ==========================================================
%% Behaviour definition
-export([ behaviour_info/1
        ]).

%% API
-export([ handle/2
        ]).

%%%_* Types ============================================================
-type(type() :: manually_blocked
              | manually_deblocked
              | manually_cleared
              | automatically_cleared
              | automatically_blocked
              | error
              | call_timeout
              | timeout).

-export_type([ type/0
             ]).

%%%_* Behaviour definition =============================================
behaviour_info(callbacks) ->
  [ {handle, 2}
  ];
behaviour_info(_Other)    ->
  undefined.

%%%_* API ==============================================================
-spec handle(Type::type(), Info::list()) -> any().
%% @doc Called when circuit breaker generates an event.
%% @end
handle(Type, _Info) ->
  error_logger:info_msg("Received ~w from circuit breaker", [Type]).

%%%_* Emacs ============================================================
%%% Local Variables:
%%% allout-layout: t
%%% erlang-indent-level: 2
%%% End:


================================================
FILE: src/circuit_breaker_sup.erl
================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Copyright 2012 Klarna AB
%%%
%%% 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.
%%%
%%% @doc Circuit breaker supervisor
%%% @copyright 2012 Klarna AB
%%% @end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%_* Module declaration ===============================================
-module(circuit_breaker_sup).

%%%_* Behaviour ========================================================
-behaviour(supervisor).

%%%_* Exports ==========================================================
%% API
-export([ start_link/0
        ]).

%% Supervisor callbacks
-export([ init/1
        ]).

%%%_* Defines ==========================================================
%% Helper macro for declaring children of supervisor
-define(CHILD(I, Type),
        {I, {I, start_link, []}, permanent, 5000, Type, [I]}).

%%%_* API ==============================================================
-spec start_link() -> {ok, pid()} | ignore | {error, Reason::term()}.
%% @doc Creates a supervisor process as part of a supervision tree.
%% The function will, among other things, ensure that the supervisor
%% is linked to the calling process (its supervisor). The created
%% supervisor process calls Module:init/1
%% @end
start_link() -> supervisor:start_link({local, ?MODULE}, ?MODULE, []).

%%%_* Supervisor callbacks =============================================
%% @hidden
init([]) ->
  {ok, {{one_for_one, 10, 20},
        [ ?CHILD(circuit_breaker, worker)
        ]}}.

%%%_* Emacs ============================================================
%%% Local Variables:
%%% allout-layout: t
%%% erlang-indent-level: 2
%%% End:


================================================
FILE: test/circuit_breaker_event_test.erl
================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Copyright 2012 Klarna AB
%%%
%%% 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.
%%%
%%% @doc Circuit breaker event test
%%% @copyright 2012 Klarna AB
%%% @end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%_* Module declaration ===============================================
-module(circuit_breaker_event_test).

%%%_* Behaviour ========================================================
-beahviour(circuit_breaker_event).

%%%_* Exports ==========================================================
%% Circuit breaker callback
-export([ handle/2
        ]).

%%%_* Callback =========================================================
%% @see circuit_breaker_event:handle/2
handle(_Type, _Info) -> ok.

%%%_* Emacs ============================================================
%%% Local Variables:
%%% allout-layout: t
%%% erlang-indent-level: 2
%%% End:


================================================
FILE: test/circuit_breaker_tests.erl
================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Copyright 2012 Klarna AB
%%%
%%% 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.
%%
%%% @doc Circuit breaker tests
%%% @copyright 2012 Klarna AB
%%% @end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%_* Module declaration ===============================================
-module(circuit_breaker_tests).

%%%_* Includes =========================================================
-include_lib("eunit/include/eunit.hrl").
-include("circuit_breaker.hrl").

%%%_* Defines ==========================================================
-define(SERVICE, service).
-define(APP,     circuit_breaker).

%%%_* Tests ============================================================
circuit_breaker_test_() ->
  {"Tests the circuit breaker functionality",
   { foreach
   , fun start/0             % setup
   , fun stop/1              % teardown
   , [ fun undefined/1
     , fun call_timeout_block/1
     , fun timeout_block/1
     , fun error_block/1
     , fun manual_block/1
     , fun manual_deblock/1
     , fun manual_clear/1
     , fun returns/1
     , fun reset/1
     , fun ignore_errors/1
     , fun info/1
     , fun info_to_text/1
     ]}}.

start() ->
  case application:start(?APP) of
    ok                            ->
      ok = application:set_env(?APP, event_handler, circuit_breaker_event_test);
    {error, {already_started, _}} ->
      circuit_breaker:clear(?SERVICE),
      already_started
  end.

stop(already_started) -> ok;
stop(_)               -> application:stop(?APP).

undefined(_Setup) ->
  [ ?_assertEqual({error, undefined}, circuit_breaker:block(?SERVICE))
  , ?_assertEqual({error, undefined}, circuit_breaker:deblock(?SERVICE))
  , ?_assertEqual({error, undefined}, circuit_breaker:clear(?SERVICE))
  , ?_assertEqual(false, circuit_breaker:disabled(?SERVICE))
  , ?_assertEqual(false, circuit_breaker:blocked(?SERVICE))
  ].

call_timeout_block(_Setup) ->
  call(),
  {_, 5} = loop_call(fun() -> timer:sleep(200) end),
  [ ?_assertEqual(false, circuit_breaker:blocked(?SERVICE))
  , ?_assert(circuit_breaker:disabled(?SERVICE))
  , ?_assertEqual({error, {circuit_breaker, ?CIRCUIT_BREAKER_CALL_TIMEOUT}},
                  call())
  ].

timeout_block(_Setup) ->
  call(),
  {_, 5} = loop_call(fun() -> {error, timeout} end),
  [ ?_assertEqual(false, circuit_breaker:blocked(?SERVICE))
  , ?_assert(circuit_breaker:disabled(?SERVICE))
  , ?_assertEqual({error, {circuit_breaker, ?CIRCUIT_BREAKER_TIMEOUT}},
                  call())
  ].

error_block(_Setup) ->
  call(),
  {_, 5} = loop_call(fun() -> {error, crash} end),
  [ ?_assertEqual(false, circuit_breaker:blocked(?SERVICE))
  , ?_assert(circuit_breaker:disabled(?SERVICE))
  , ?_assertEqual({error, {circuit_breaker, ?CIRCUIT_BREAKER_ERROR}},
                  call())
  ].

manual_block(_Setup) ->
  call(),
  circuit_breaker:block(?SERVICE),
  [ ?_assert(circuit_breaker:blocked(?SERVICE))
  , ?_assert(circuit_breaker:disabled(?SERVICE))
  , ?_assertEqual({error, {circuit_breaker, ?CIRCUIT_BREAKER_BLOCKED}}, call())
  ].

manual_deblock(_Setup) ->
  call(),
  circuit_breaker:block(?SERVICE),
  circuit_breaker:deblock(?SERVICE),
  [ ?_assertEqual(false, circuit_breaker:blocked(?SERVICE))
  , ?_assertEqual(false, circuit_breaker:disabled(?SERVICE))
  , ?_assert(call())
  ].

manual_clear(_Setup) ->
  call(),
  {_, 5} = loop_call(fun() -> {error, crash} end),
  circuit_breaker:clear(?SERVICE),
  [ ?_assertEqual(false, circuit_breaker:blocked(?SERVICE))
  , ?_assertEqual(false, circuit_breaker:disabled(?SERVICE))
  , ?_assert(call())
  ].

returns(_Setup) ->
  [ ?_assert(call())
  , ?_assertEqual({error, timeout}, call(fun() -> timer:sleep(200) end))
  , ?_assertEqual({error, timeout}, call(fun() -> {error, timeout} end))
  , ?_assertEqual({error, some_error}, call(fun() -> {error, some_error} end))
  , ?_assertException(exit, reason, call(fun() -> exit(reason) end))
  , ?_assertException(error, reason, call(fun() -> error(reason) end))
  , ?_assertException(throw, reason, call(fun() -> throw(reason) end))
  ].

reset(_Setup) ->
  {_, 5} = loop_call(fun() -> {error, timeout} end),
  [ ?_assert(retry(fun() ->
                       false =:= circuit_breaker:disabled(?SERVICE)
                   end, 1000, 10))
  ].

retry(F, T, N) when N > 0 ->
  case F() of
    Res when Res =:= false
           ; Res =:= error
           ; element(1, Res) =:= error ->
      timer:sleep(T),
      retry(F, T, N-1);
    Res ->
      Res
  end;
retry(_F, _T, 0) -> false.

ignore_errors(_Setup) ->
  call(),
  ok = loop_call(fun() -> {error, some_error} end),
  [ ?_assertEqual(false, circuit_breaker:disabled(?SERVICE))
  ].

info(_Setup) ->
  call(),
  [ ?_assertEqual(ok, circuit_breaker:info())
  ].

info_to_text(_Setup) ->
  call(),
  Result = iolist_to_binary(circuit_breaker:info_to_text()),
  Expected =
    <<"Service                         Status          Error    Timeout  CallTime\n"
    , "------------------------------- --------------- -------- -------- --------\n"
    , "service                         OK              0        0        0       \n"
    >>,
  [ ?_assertEqual(Expected, Result)
  ].

%%%_* Helpers ==========================================================
call() -> call(fun() -> true end).

%% Use custom values to test that these are used
call(F) ->
  circuit_breaker:call( ?SERVICE, F, 100, fun() -> true end, 2000
                      , [ {n_error,           5}
                        , {n_timeout,         5}
                        , {n_call_timeout,    5}
                        , {ignore_errors,     [some_error]}
                        ]
                      ).

loop_call(F) -> loop_call(F, 0).

loop_call(_F, 20) -> ok;
loop_call(F, N)   ->
  case call(F) of
    {error, {circuit_breaker, _}} = Error -> {Error, N};
    _                                     -> loop_call(F, N + 1)
  end.

%%%_* Emacs ============================================================
%%% Local Variables:
%%% allout-layout: t
%%% erlang-indent-level: 2
%%% End: