From 29199e7e6e93e242c9d9fecc7db67bb3e170d6d6 Mon Sep 17 00:00:00 2001
From: Siraaj Khandkar <siraaj@khandkar.net>
Date: Thu, 26 Jul 2012 20:22:35 -0400
Subject: [PATCH] Fixed out-of-order message handling.

---
 001/src/life_cell.erl | 38 +++++++++++++++++++++++++++-----------
 001/src/life_time.erl | 12 +++++-------
 2 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/001/src/life_cell.erl b/001/src/life_cell.erl
index 2ffda4b..4771064 100644
--- a/001/src/life_cell.erl
+++ b/001/src/life_cell.erl
@@ -15,7 +15,7 @@
         ]).
 
 
--record(state, {id              :: integer()
+-record(state, {cell_id         :: integer()
                ,name            :: string()
                ,cell_state      :: 0 | 1
                ,neighbors       :: list(atom())
@@ -30,7 +30,7 @@
 %% API
 %% ============================================================================
 
-start_link({_ID, Name, _NeighborNames}=Datum) ->
+start_link({_, Name, _}=Datum) ->
     ServerName = {local, Name},
     Args = [Datum],
     Opts = [],
@@ -41,8 +41,8 @@ start_link({_ID, Name, _NeighborNames}=Datum) ->
 %% Callbacks
 %% ============================================================================
 
-init([{ID, Name, NeighborNames}]) ->
-    State = #state{id              = ID
+init([{CellID, Name, NeighborNames}]) ->
+    State = #state{cell_id         = CellID
                   ,name            = Name
                   ,cell_state      = crypto:rand_uniform(0, 2)
                   ,neighbors       = NeighborNames
@@ -70,17 +70,34 @@ handle_cast({next_gen, GenID},
           ,neighbors=Neighbors
           ,num_neighbors=NumNeighbors
           }=State) ->
-    ok = cast_all(Neighbors, {request_state, Name}),
+
+    ok = cast_all(Neighbors, {request_state, GenID, Name}),
     {noreply, State#state{replies_pending=NumNeighbors, gen_id=GenID}};
 
+%% If we receive this before we receive next_gen, throw it back in the queue.
+%% (Took me a while to realize this, but sometimes it is possible. The more
+%% there're cells, the more likely this is to happen.)
+handle_cast({request_state, GenID, _Requester}=Msg,
+    #state{gen_id=MyGenID
+          ,name=Name
+          }=State) when GenID =/= MyGenID->
 
-handle_cast({request_state, Requester}, State) ->
-    ok = gen_server:cast(Requester, {response_state, State#state.cell_state}),
+    gen_server:cast(Name, Msg),
     {noreply, State};
 
+%% Now that we can be sure that this request is for the current generation, we
+%% can handle it
+handle_cast({request_state, GenID, Requester},
+    #state{gen_id=MyGenID
+          ,cell_state=CellState
+          }=State) when GenID =:= MyGenID->
 
-handle_cast({response_state, NeighborState},
-    #state{id=ID
+    ok = gen_server:cast(Requester, {response_state, MyGenID, CellState}),
+    {noreply, State};
+
+handle_cast({response_state, GenID, NeighborState},
+    #state{cell_id=CellID
+          ,gen_id=GenID
           ,replies_pending=Pending
           ,cell_state=CellState
           ,live_neighbors=LiveNeighbors
@@ -96,7 +113,7 @@ handle_cast({response_state, NeighborState},
     case NewPending of
         0 ->
             NewCellState = new_state(CellState, NewLiveNeighbors),
-            ok = life_time:report_state(ID, NewCellState),
+            ok = life_time:report_state(CellID, GenID, NewCellState),
 
             {noreply, NewState#state{live_neighbors=0
                                     ,cell_state=NewCellState
@@ -107,7 +124,6 @@ handle_cast({response_state, NeighborState},
             {noreply, NewState}
     end;
 
-
 handle_cast(_Msg, State) ->
     {noreply, State}.
 
diff --git a/001/src/life_time.erl b/001/src/life_time.erl
index b47073c..49ab646 100644
--- a/001/src/life_time.erl
+++ b/001/src/life_time.erl
@@ -4,7 +4,7 @@
 
 %% API
 -export([start_link/3
-        ,report_state/2
+        ,report_state/3
         ]).
 
 %% Callbacks
@@ -45,8 +45,8 @@ start_link(X, Y, Cells) ->
     gen_server:start_link(ServerName, ?MODULE, Args, Opts).
 
 
-report_state(CellID, CellState) ->
-    gen_server:cast(?MODULE, {report_state, {CellID, CellState}}).
+report_state(CellID, GenID, CellState) ->
+    gen_server:cast(?MODULE, {report_state, {CellID, GenID, CellState}}).
 
 
 %% ============================================================================
@@ -89,7 +89,7 @@ handle_cast(next_gen,
     ok = cast_all(Cells, {next_gen, NewGenID}),
     {noreply, State#state{replies_pending=NumCells, gen_id=NewGenID}};
 
-handle_cast({report_state, {ID, CellState}},
+handle_cast({report_state, {CellID, GenID, CellState}},
     #state{x=X
           ,y=Y
           ,state_pairs=StatePairs
@@ -98,7 +98,7 @@ handle_cast({report_state, {ID, CellState}},
           ,num_cells=NumCells
           }=State) ->
 
-    NewStatePairs = [{ID, CellState} | StatePairs],
+    NewStatePairs = [{CellID, CellState} | StatePairs],
     NewRepliesPending = RepliesPending - 1,
     NewState = State#state{replies_pending=NewRepliesPending},
 
@@ -115,9 +115,7 @@ handle_cast({report_state, {ID, CellState}},
                 [X, Y, NumCells, GenID]
             ),
             ok = do_print_bar(X),
-
             ok = do_print_state_chars(X, StateChars),
-
             ok = timer:sleep(?INTERVAL),
             schedule_next_gen(),
             {noreply, NewState#state{state_pairs=[]}};
-- 
2.20.1