elibs/resource_manager.erl

   1 %%%-------------------------------------------------------------------
   2 %%% File    : /Users/dfayram/Projects/concilium/elibs/resource_manager.erl
   3 %%% Author  : David Fayram
   4 %%%-------------------------------------------------------------------
   5 -module(resource_manager).
   6 -behaviour(gen_server).
   7
   8 %% API exports
   9 -export([start_link/3, start/3,nodes/0,nodecount/0,change_nodecount/1,cycle/0,cycle/1]).
  10
  11 %% gen_server callback exports
  12 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  13          terminate/2, code_change/3]).
  14
  15 %% Erlang records are ugly.
  16 -record(state, {generator = fun() -> undefined end,
  17                 terminator = fun(_) -> undefined end,
  18                 nodecount = 1,
  19                 nodes = [],
  20                 term_hook = fun(_) -> undefined end
  21                }).
  22
  23 %% External call functions
  24
  25 % Note the local server, one of these should run on every
  26 % node serving up rails responders.
  27 start_link(Generator, Terminator, NumNodes) ->
  28     gen_server:start_link({local, ?MODULE}, ?MODULE, [Generator, Terminator, NumNodes], []).
  29 start(Generator, Terminator, NumNodes) ->
  30     gen_server:start({local, ?MODULE}, ?MODULE, [Generator, Terminator, NumNodes], []).
  31
  32 nodes() -> gen_server:call(?MODULE, nodes).
  33 nodecount() -> gen_server:call(?MODULE, nodecount).
  34 change_nodecount(NewNodecount) -> gen_server:cast(?MODULE, {change_nodecount, NewNodecount}).
  35 cycle() -> gen_server:cast(?MODULE, cycle).
  36 cycle(Node) -> gen_server:cast({?MODULE, Node}, cycle).
  37
  38 %% GEN_SERVER callbacks.
  39 init([Generator, Terminator, NumNodes]) ->
  40     process_flag(trap_exit, true),
  41     Nodes = spawn_nodes(Generator, NumNodes),
  42     {ok, #state{generator = Generator, nodecount = NumNodes,
  43                 nodes = Nodes, terminator = Terminator}}.
  44
  45 handle_call(term_hook, _From, State) ->
  46   {reply, State#state.term_hook, State};
  47 handle_call({term_hook, Hook}, _From, State) when is_function(Hook, 1) ->
  48   {reply, State#state.term_hook, State#state{term_hook = Hook}};
  49 handle_call(nodecount,_From,State) ->
  50   {reply, State#state.nodecount, State};
  51 handle_call(nodes, _From, State) ->
  52   {reply, State#state.nodes, State}.
  53
  54 handle_cast(cycle, State) ->
  55   drop_nodes(State#state.terminator, State#state.nodes),
  56   {noreply, State#state{nodes=spawn_nodes(State#state.generator, State#state.nodecount)}};
  57 handle_cast({change_nodecount, NewCount}, S) when is_number(NewCount) ->
  58   Count = S#state.nodecount,
  59   if
  60     NewCount > Count ->
  61       {noreply,
  62         S#state{nodecount = NewCount,
  63                 nodes = spawn_nodes(S#state.generator, NewCount - Count) ++ S#state.nodes}};
  64     NewCount < Count ->
  65       {ToKill, ToKeep} = lists:split(NewCount - Count, S#state.nodes),
  66       drop_nodes(S#state.terminator, ToKill),
  67       {noreply, S#state{nodecount=NewCount, nodes=ToKeep}};
  68     true ->
  69       {noreply, S}
  70   end.
  71
  72 handle_info({'EXIT', Pid, _Reason}, S) ->
  73   Term = S#state.terminator,
  74   Membership = lists:any(fun(X) -> X =:= Pid end, S#state.nodes),
  75   if
  76     Membership ->
  77       Term(Pid),
  78       Res = lists:delete(Pid, S#state.nodes),
  79       NewNode = spawn_linked_node(S#state.generator),
  80       {noreply, S#state{nodes=[NewNode|Res]}};
  81     true ->
  82       {noreply, S}
  83   end;
  84 handle_info(Any,S) ->
  85   io:format("Got INFO ~p~n", [Any]),
  86   {noreply, S}.
  87
  88 terminate(_Reason, _State) ->
  89     ok.
  90
  91 code_change(_OldVsn, State, _Extra) ->
  92     {ok, State}.
  93
  94 %% Utility functions
  95
  96 spawn_linked_node(Generator) ->
  97   Node = Generator(),
  98   link(Node),
  99   Node.
 100
 101 spawn_nodes(Generator,NumNodes) ->
 102   spawn_nodes(Generator,NumNodes,[]).
 103
 104 spawn_nodes(_Generator,0,Acc) -> Acc;
 105 spawn_nodes(Generator,NumNodes,Acc) -> spawn_nodes(Generator,NumNodes - 1, [spawn_linked_node(Generator)|Acc]).
 106
 107 drop_nodes(Terminator, Nodes) ->
 108   Killer = fun(Node) -> unlink(Node), Terminator(Node) end,
 109   lists:map(Killer, Nodes).