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%%%------------------------------------------------------------------- |
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%%% @author Uvarov Michael <arcusfelis@gmail.com> |
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%%% @copyright (C) 2013, Uvarov Michael |
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%%% @doc Allocates unique ids for each node. |
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%%% @end |
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%%%------------------------------------------------------------------- |
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-module(ejabberd_node_id). |
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-export([start/0, node_id/0]). |
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-include("mongoose.hrl"). |
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-include("jlib.hrl"). |
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%%==================================================================== |
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%% API |
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%%==================================================================== |
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-type nodeid() :: non_neg_integer(). |
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-record(node, {name :: atom(), |
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id :: nodeid() |
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}). |
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start() -> |
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mnesia:create_table(node, |
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[{ram_copies, [node()]}, |
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{type, set}, |
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{attributes, record_info(fields, node)}]), |
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mnesia:add_table_copy(node, node(), ram_copies), |
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register_node(node()), |
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ok. |
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-spec register_node(atom()) -> 'ok'. |
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register_node(NodeName) -> |
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{atomic, _} = mnesia:transaction(fun() -> |
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case mnesia:read(node, NodeName) of |
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[] -> |
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mnesia:write(#node{name = NodeName, id = next_node_id()}); |
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[_] -> ok |
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end |
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end), |
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ok. |
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%% @doc Return an integer node ID. |
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-spec node_id() -> {ok, nodeid()}. |
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node_id() -> |
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%% Save result into the process's memory space. |
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case get(node_id) of |
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undefined -> |
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{ok, NodeId} = select_node_id(node()), |
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put(node_id, NodeId), |
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{ok, NodeId}; |
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NodeId -> |
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{ok, NodeId} |
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end. |
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-spec next_node_id() -> nodeid(). |
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next_node_id() -> |
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max_node_id() + 1. |
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-spec max_node_id() -> nodeid(). |
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max_node_id() -> |
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mnesia:foldl(fun(#node{id=Id}, Max) -> max(Id, Max) end, 0, node). |
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-spec select_node_id(NodeName :: atom() |
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) -> {'error', 'not_found'} | {'ok', nodeid()}. |
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select_node_id(NodeName) -> |
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case mnesia:dirty_read(node, NodeName) of |
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[#node{id=Id}] -> {ok, Id}; |
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[] -> {error, not_found} |
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end. |