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[cellular-automata.git] / life / 001 / src / life_cell.erl
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1-module(life_cell).
2-behaviour(gen_server).
3
4
5%% API
6-export([start_link/1]).
7
8%% Callbacks
9-export([init/1
10 ,handle_call/3
11 ,handle_cast/2
12 ,handle_info/2
13 ,terminate/2
14 ,code_change/3
15 ]).
16
17
18-record(state, {cell_id :: integer()
19 ,name :: string()
20 ,cell_state :: 0 | 1
21 ,neighbors :: list(atom())
22 ,live_neighbors :: integer()
23 ,num_neighbors :: integer()
24 ,replies_pending :: integer()
25 ,gen_id :: integer()
26 ,early_msgs :: list()
27 }).
28
29
30%% ============================================================================
31%% API
32%% ============================================================================
33
34start_link({_, Name, _}=Datum) ->
35 ServerName = {local, Name},
36 Args = [Datum],
37 Opts = [],
38 gen_server:start_link(ServerName, ?MODULE, Args, Opts).
39
40
41%% ============================================================================
42%% Callbacks (unused)
43%% ============================================================================
44
45handle_call(_Msg, _From, State) -> {reply, ok, State}.
46handle_info(_Msg, State) -> {noreply, State}.
47code_change(_Old, State, _Other) -> {ok, State}.
48terminate(_Reason, State) -> {ok, State}.
49
50
51%% ============================================================================
52%% Callbacks
53%% ============================================================================
54
55init([{CellID, Name, NeighborNames}]) ->
56 State = #state{cell_id = CellID
57 ,name = Name
58 ,cell_state = crypto:rand_uniform(0, 2)
59 ,neighbors = NeighborNames
60 ,num_neighbors = length(NeighborNames)
61 ,live_neighbors = 0
62 ,replies_pending = 0
63 ,early_msgs = []
64 },
65 {ok, State}.
66
67
68handle_cast({next_gen, GenID},
69 #state{name=Name
70 ,cell_state=CellState
71 ,neighbors=Neighbors
72 ,num_neighbors=NumNeighbors
73 ,early_msgs=EarlyMsgs
74 }=State) ->
75
76 ok = life_lib:cast_one2all(Neighbors, {state_broadcast, GenID, CellState}),
77
78 % Put stashed messages back in the mailbox,
79 % now that we're ready to handle them
80 ok = life_lib:cast_all2one(Name, EarlyMsgs),
81
82 NewState = State#state{replies_pending=NumNeighbors
83 ,gen_id=GenID
84 ,early_msgs=[]
85 },
86
87 {noreply, NewState};
88
89
90%% If we receive 'state_broadcast' before we receive 'next_gen',
91%% stash it until we do.
92%%
93%% Took me a while to realize this, but sometimes it is possible. The more
94%% there're cells, the more likely this is to happen.
95%%
96handle_cast({state_broadcast, ReceivedGenID, _NeighborState}=Msg,
97 #state{gen_id=GenID
98 ,early_msgs=EarlyMsgs
99 }=State) when GenID =/= ReceivedGenID ->
100
101 {noreply, State#state{early_msgs=[Msg|EarlyMsgs]}};
102
103
104%% Now that we can be sure that this request is for the current generation, we
105%% can handle it
106handle_cast({state_broadcast, GenID, NeighborState},
107 #state{cell_id=CellID
108 ,gen_id=GenID
109 ,replies_pending=Pending
110 ,cell_state=CellState
111 ,live_neighbors=LiveNeighbors
112 }=State) ->
113
114 NewPending = Pending - 1,
115 NewLiveNeighbors = LiveNeighbors + NeighborState,
116
117 NewState = State#state{replies_pending=NewPending
118 ,live_neighbors=NewLiveNeighbors
119 },
120
121 case NewPending of
122 0 ->
123 NewCellState = new_state(CellState, NewLiveNeighbors),
124 ok = life_time:report_state(CellID, GenID, NewCellState),
125
126 {noreply, NewState#state{live_neighbors=0
127 ,cell_state=NewCellState
128 }
129 };
130
131 _N ->
132 {noreply, NewState}
133 end;
134
135
136handle_cast(_Msg, State) ->
137 {noreply, State}.
138
139
140%% ============================================================================
141%% Internal
142%% ============================================================================
143
144new_state(1, LiveNeighbors) when LiveNeighbors < 2 -> 0;
145new_state(1, LiveNeighbors) when LiveNeighbors < 4 -> 1;
146new_state(1, LiveNeighbors) when LiveNeighbors > 3 -> 0;
147new_state(0, LiveNeighbors) when LiveNeighbors =:= 3 -> 1;
148new_state(State, _LiveNeighbors) -> State.
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