1 files changed, 113 insertions, 0 deletions
diff --git a/learn-you-some-erlang/pool/ppool_serv.erl b/learn-you-some-erlang/pool/ppool_serv.erl
new file mode 100644
index 0000000..512b49f
--- /dev/null
+++ b/learn-you-some-erlang/pool/ppool_serv.erl
@@ -0,0 +1,113 @@
+-module(ppool_serv).
+-behaviour(gen_server).
+-export([start/4, start_link/4, run/2, sync_queue/2, async_queue/2, stop/1]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
+         code_change/3, terminate/2]).
+
+%% The friendly supervisor is started dynamically!
+-define(SPEC(MFA),
+        {worker_sup,
+         {ppool_worker_sup, start_link, [MFA]},
+          temporary,
+          10000,
+          supervisor,
+          [ppool_worker_sup]}).
+
+-record(state, {limit=0,
+                sup,
+                refs,
+                queue=queue:new()}).
+
+start(Name, Limit, Sup, MFA) when is_atom(Name), is_integer(Limit) ->
+    gen_server:start({local, Name}, ?MODULE, {Limit, MFA, Sup}, []).
+
+start_link(Name, Limit, Sup, MFA) when is_atom(Name), is_integer(Limit) ->
+    gen_server:start_link({local, Name}, ?MODULE, {Limit, MFA, Sup}, []).
+
+run(Name, Args) ->
+    gen_server:call(Name, {run, Args}).
+
+sync_queue(Name, Args) ->
+    gen_server:call(Name, {sync, Args}, infinity).
+
+async_queue(Name, Args) ->
+    gen_server:cast(Name, {async, Args}).
+
+stop(Name) ->
+    gen_server:call(Name, stop).
+
+%% Gen server
+init({Limit, MFA, Sup}) ->
+    %% We need to find the Pid of the worker supervisor from here,
+    %% but alas, this would be calling the supervisor while it waits for us!
+    self() ! {start_worker_supervisor, Sup, MFA},
+    {ok, #state{limit=Limit, refs=gb_sets:empty()}}.
+
+handle_call({run, Args}, _From, S = #state{limit=N, sup=Sup, refs=R}) when N > 0 ->
+    {ok, Pid} = supervisor:start_child(Sup, Args),
+    Ref = erlang:monitor(process, Pid),
+    {reply, {ok,Pid}, S#state{limit=N-1, refs=gb_sets:add(Ref,R)}};
+handle_call({run, _Args}, _From, S=#state{limit=N}) when N =< 0 ->
+    {reply, noalloc, S};
+
+handle_call({sync, Args}, _From, S = #state{limit=N, sup=Sup, refs=R}) when N > 0 ->
+    {ok, Pid} = supervisor:start_child(Sup, Args),
+    Ref = erlang:monitor(process, Pid),
+    {reply, {ok,Pid}, S#state{limit=N-1, refs=gb_sets:add(Ref,R)}};
+handle_call({sync, Args},  From, S = #state{queue=Q}) ->
+    {noreply, S#state{queue=queue:in({From, Args}, Q)}};
+
+handle_call(stop, _From, State) ->
+    {stop, normal, ok, State};
+handle_call(_Msg, _From, State) ->
+    {noreply, State}.
+
+
+handle_cast({async, Args}, S=#state{limit=N, sup=Sup, refs=R}) when N > 0 ->
+    {ok, Pid} = supervisor:start_child(Sup, Args),
+    Ref = erlang:monitor(process, Pid),
+    {noreply, S#state{limit=N-1, refs=gb_sets:add(Ref,R)}};
+handle_cast({async, Args}, S=#state{limit=N, queue=Q}) when N =< 0 ->
+    {noreply, S#state{queue=queue:in(Args,Q)}};
+
+handle_cast(_Msg, State) ->
+    {noreply, State}.
+
+handle_info({'DOWN', Ref, process, _Pid, _}, S = #state{refs=Refs}) ->
+    io:format("received down msg~n"),
+    case gb_sets:is_element(Ref, Refs) of
+        true ->
+            handle_down_worker(Ref, S);
+        false -> %% Not our responsibility
+            {noreply, S}
+    end;
+handle_info({start_worker_supervisor, Sup, MFA}, S = #state{}) ->
+    {ok, Pid} = supervisor:start_child(Sup, ?SPEC(MFA)),
+    link(Pid),
+    {noreply, S#state{sup=Pid}};
+handle_info(Msg, State) ->
+    io:format("Unknown msg: ~p~n", [Msg]),
+    {noreply, State}.
+
+code_change(_OldVsn, State, _Extra) ->
+    {ok, State}.
+
+terminate(_Reason, _State) ->
+    ok.
+
+handle_down_worker(Ref, S = #state{limit=L, sup=Sup, refs=Refs}) ->
+    case queue:out(S#state.queue) of
+        {{value, {From, Args}}, Q} ->
+            {ok, Pid} = supervisor:start_child(Sup, Args),
+            NewRef = erlang:monitor(process, Pid),
+            NewRefs = gb_sets:insert(NewRef, gb_sets:delete(Ref,Refs)),
+            gen_server:reply(From, {ok, Pid}),
+            {noreply, S#state{refs=NewRefs, queue=Q}};
+        {{value, Args}, Q} ->
+            {ok, Pid} = supervisor:start_child(Sup, Args),
+            NewRef = erlang:monitor(process, Pid),
+            NewRefs = gb_sets:insert(NewRef, gb_sets:delete(Ref,Refs)),
+            {noreply, S#state{refs=NewRefs, queue=Q}};
+        {empty, _} ->
+            {noreply, S#state{limit=L+1, refs=gb_sets:delete(Ref,Refs)}}
+    end.