emqx_sequence.erl

%%--------------------------------------------------------------------
%% Copyright (c) 2018-2021 EMQ Technologies Co., Ltd. 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.
%%--------------------------------------------------------------------

-module(emqx_sequence).

-export([ create/1
        , nextval/2
        , currval/2
        , reclaim/2
        , delete/1
        ]).

-export_type([seqid/0]).

-type(key() :: term()).

-type(name() :: atom()).

-type(seqid() :: non_neg_integer()).

%%--------------------------------------------------------------------
%% APIs
%%--------------------------------------------------------------------

%% @doc Create a sequence.
-spec(create(name()) -> ok).
create(Name) ->
    emqx_tables:new(Name, [public, set, {write_concurrency, true}]).

%% @doc Next value of the sequence.
-spec(nextval(name(), key()) -> seqid()).
nextval(Name, Key) ->
    ets:update_counter(Name, Key, {2, 1}, {Key, 0}).

%% @doc Current value of the sequence.
-spec(currval(name(), key()) -> seqid()).
currval(Name, Key) ->
    try ets:lookup_element(Name, Key, 2)
    catch
        error:badarg -> 0
    end.

%% @doc Reclaim a sequence id.
-spec(reclaim(name(), key()) -> seqid()).
reclaim(Name, Key) ->
    try ets:update_counter(Name, Key, {2, -1, 0, 0}) of
        0 -> ets:delete_object(Name, {Key, 0}), 0;
        I -> I
    catch
        error:badarg -> 0
    end.

%% @doc Delete the sequence.
-spec(delete(name()) -> boolean()).
delete(Name) ->
    case ets:info(Name, name) of
        Name -> ets:delete(Name);
        undefined -> false
    end.