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]).
  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
  37 %% GEN_SERVER callbacks.
  38 init([Generator, Terminator, NumNodes]) ->
  39     process_flag(trap_exit, true),
  40     Nodes = spawn_nodes(Generator, NumNodes),
  41     {ok, #state{generator = Generator, nodecount = NumNodes,
  42                 nodes = Nodes, terminator = Terminator}}.
  43
  44 handle_call(term_hook, _From, State) ->
  45   {reply, State#state.term_hook, State};
  46 handle_call({term_hook, Hook}, _From, State) when is_function(Hook, 1) ->
  47   {reply, State#state.term_hook, State#state{term_hook = Hook}};
  48 handle_call(nodecount,_From,State) ->
  49   {reply, State#state.nodecount, State};
  50 handle_call(nodes, _From, State) ->
  51   {reply, State#state.nodes, State}.
  52
  53 handle_cast(cycle, State) ->
  54   drop_nodes(State#state.terminator, State#state.nodes),
  55   {noreply, State#state{nodes=spawn_nodes(State#state.generator, State#state.nodecount)}};
  56 handle_cast({change_nodecount, NewCount}, S) when is_number(NewCount) ->
  57   Count = S#state.nodecount,
  58   if
  59     NewCount > Count ->
  60       {noreply,
  61         S#state{nodecount = NewCount,
  62                 nodes = spawn_nodes(S#state.generator, NewCount - Count) ++ S#state.nodes}};
  63     NewCount < Count ->
  64       {ToKill, ToKeep} = lists:split(NewCount - Count, S#state.nodes),
  65       drop_nodes(S#state.terminator, ToKill),
  66       {noreply, S#state{nodecount=NewCount, nodes=ToKeep}};
  67     true ->
  68       {noreply, S}
  69   end.
  70
  71 handle_info({'EXIT', Pid, _Reason}, S) ->
  72   Term = S#state.terminator,
  73   Membership = lists:any(fun(X) -> X =:= Pid end, S#state.nodes),
  74   if
  75     Membership ->
  76       Term(Pid),
  77       Res = lists:delete(Pid, S#state.nodes),
  78       NewNode = spawn_linked_node(S#state.generator),
  79       {noreply, S#state{nodes=[NewNode|Res]}};
  80     true ->
  81       {noreply, S}
  82   end;
  83 handle_info(Any,S) ->
  84   io:format("Got INFO ~p~n", [Any]),
  85   {noreply, S}.
  86
  87 terminate(_Reason, _State) ->
  88     ok.
  89
  90 code_change(_OldVsn, State, _Extra) ->
  91     {ok, State}.
  92
  93 %% Utility functions
  94
  95 spawn_linked_node(Generator) ->
  96   Node = Generator(),
  97   link(Node),
  98   Node.
  99
 100 spawn_nodes(Generator,NumNodes) ->
 101   spawn_nodes(Generator,NumNodes,[]).
 102
 103 spawn_nodes(_Generator,0,Acc) -> Acc;
 104 spawn_nodes(Generator,NumNodes,Acc) -> spawn_nodes(Generator,NumNodes - 1, [spawn_linked_node(Generator)|Acc]).
 105
 106 drop_nodes(Terminator, Nodes) ->
 107   Killer = fun(Node) -> unlink(Node), Terminator(Node) end,
 108   lists:map(Killer, Nodes).