session_manager.erl

-module(session_manager).

-behaviour(gen_server).

%% API
-export([start_link/0]).
-export([set/1, get/1]).

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

-define(SERVER, ?MODULE). 

-record(state, {}).

-record(user, {userid, pid}).

set({UserID, Pid, Node}) ->
    mnesia:dirty_write(#user{userid = UserID,
                             pid = {Pid, Node}}).
    
get({UserID}) ->
    mnesia:dirty_read({user, UserID}).


start_link() ->
    gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).

init([]) ->
    mnesia:create_table(user, 
                        [
                         {ram_copies, [node()]},
                         {attributes, record_info(fields, user)}
                        ]),
    mnesia:subscribe({table, user, simple}),
    {ok, #state{}}.


handle_call(_Request, _From, State) ->
    Reply = ok,
    {reply, Reply, State}.

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

handle_info({mnesia_table_event, {write, #user{pid = {_, Node}}, _}}, State) ->
    erlang:monitor_node(Node, true),
    {noreply, State};

handle_info({nodedown, Node}, State) ->
    F = fun() ->
                ES = mnesia:select(user, 
                                   [{#user{userid = '_',pid = {'_','$1'}},
                                    [{'==','$1',Node}],
                                    ['$_']}]),
                [mnesia:delete({user, U1#user.userid}) || U1 <- ES]
        end,
    mnesia:async_dirty(F),
    {noreply, State};

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

terminate(_Reason, _State) ->
    ok.

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