From 90c656fd3097272d1e574da3f5944d60b476e418 Mon Sep 17 00:00:00 2001
From: Adam Kocoloski <adam@cloudant.com>
Date: Fri, 2 Dec 2011 16:19:44 -0500
Subject: Fork new OS processes outside proc_manager loop

---
 apps/couch/src/couch_proc_manager.erl | 62 +++++++++++++++++++++++++----------
 1 file changed, 45 insertions(+), 17 deletions(-)

diff --git a/apps/couch/src/couch_proc_manager.erl b/apps/couch/src/couch_proc_manager.erl
index 509da9ba..0f35422b 100644
--- a/apps/couch/src/couch_proc_manager.erl
+++ b/apps/couch/src/couch_proc_manager.erl
@@ -3,7 +3,7 @@
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, 
     code_change/3]).
 
--export([start_link/0, get_proc_count/0]).
+-export([start_link/0, get_proc_count/0, new_proc/2, new_proc/4]).
 
 -include("couch_db.hrl").
 
@@ -25,34 +25,37 @@ handle_call(get_table, _From, State) ->
 handle_call(get_proc_count, _From, State) ->
     {reply, ets:info(State#state.tab, size), State};
 
-handle_call({get_proc, #doc{body={Props}}=DDoc, DDocKey}, {Client, _}, State) ->
+handle_call({get_proc, #doc{body={Props}}=DDoc, DDocKey}, From, State) ->
     Lang = couch_util:get_value(<<"language">>, Props, <<"javascript">>),
     try get_procs(State#state.tab, Lang) of
+    [] ->
+        spawn_link(?MODULE, new_proc, [From, Lang, DDoc, DDocKey]),
+        {noreply, State};
     Procs ->
         case proc_with_ddoc(DDoc, DDocKey, Procs) of
         {ok, Proc0} ->
+            Client = element(1, From),
             Proc = Proc0#proc{client = erlang:monitor(process, Client)},
             ets:insert(State#state.tab, Proc),
             {reply, {ok, Proc, get_query_server_config()}, State};
         {error, Reason} ->
             {reply, {error, Reason}, State}
         end
-    catch {unknown_query_language, _} ->
-        {reply, {unknown_query_language, Lang}, State};
-    error:Reason ->
+    catch error:Reason ->
         ?LOG_ERROR("~p ~p ~p", [?MODULE, Reason, erlang:get_stacktrace()]),
         {reply, {error, Reason}, State}
     end;
 
-handle_call({get_proc, Lang}, {Client, _}, State) ->
+handle_call({get_proc, Lang}, {Client, _} = From, State) ->
     try get_procs(State#state.tab, Lang) of
+    [] ->
+        spawn_link(?MODULE, new_proc, [From, Lang]),
+        {noreply, State};
     [Proc0|_] ->
         Proc = Proc0#proc{client = erlang:monitor(process, Client)},
         ets:insert(State#state.tab, Proc),
         {reply, {ok, Proc, get_query_server_config()}, State}
-    catch {unknown_query_language, _} ->
-        {reply, {unknown_query_language, Lang}, State};
-    error:Reason ->
+    catch error:Reason ->
         ?LOG_ERROR("~p ~p ~p", [?MODULE, Reason, erlang:get_stacktrace()]),
         {reply, {error, Reason}, State}
     end;
@@ -74,6 +77,13 @@ handle_call(_Call, _From, State) ->
 handle_cast(_Msg, State) ->
     {noreply, State}.
 
+handle_info({'EXIT', _, {ok, Proc0, {Client,_} = From}}, State) ->
+    link(Proc0#proc.pid),
+    Proc = Proc0#proc{client = erlang:monitor(process, Client)},
+    gen_server:reply(From, {ok, Proc, get_query_server_config()}),
+    ets:insert(State#state.tab, Proc),
+    {noreply, State};
+
 handle_info({'EXIT', Pid, Reason}, State) ->
     ?LOG_INFO("~p ~p died ~p", [?MODULE, Pid, Reason]),
     ets:delete(State#state.tab, Pid),
@@ -115,20 +125,37 @@ maybe_reuse_proc(Tab, #proc{pid = Pid} = Proc) ->
 get_procs(Tab, Lang) when is_binary(Lang) ->
     get_procs(Tab, binary_to_list(Lang));
 get_procs(Tab, Lang) when is_list(Lang) ->
-    case ets:match_object(Tab, #proc{lang=Lang, client=nil, _='_'}) of
-    [] ->
-        {ok, NewProc} = new_proc(Lang), % check OS process limit
-        [NewProc];
-    Procs ->
-        Procs
+    ets:match_object(Tab, #proc{lang=Lang, client=nil, _='_'}).
+
+new_proc(From, Lang) ->
+    case new_proc_int(From, Lang) of
+    {ok, Proc} ->
+        exit({ok, Proc, From});
+    Error ->
+        gen_server:reply(From, {error, Error})
+    end.
+
+new_proc(From, Lang, DDoc, DDocKey) ->
+    case new_proc_int(From, Lang) of
+    {ok, NewProc} ->
+        case proc_with_ddoc(DDoc, DDocKey, [NewProc]) of
+        {ok, Proc} ->
+            exit({ok, Proc, From});
+        {error, Reason} ->
+            gen_server:reply(From, {error, Reason})
+        end;
+    Error ->
+        gen_server:reply(From, {error, Error})
     end.
 
-new_proc(Lang) when is_list(Lang) ->
+new_proc_int(From, Lang) when is_binary(Lang) ->
+    new_proc_int(From, binary_to_list(Lang));
+new_proc_int(From, Lang) when is_list(Lang) ->
     case couch_config:get("query_servers", Lang) of
     undefined ->
         case couch_config:get("native_query_servers", Lang) of
         undefined ->
-            throw({unknown_query_language, Lang});
+            gen_server:reply(From, {unknown_query_language, Lang});
         SpecStr ->
             {ok, {M,F,A}} = couch_util:parse_term(SpecStr),
             {ok, Pid} = apply(M, F, A),
@@ -147,6 +174,7 @@ make_proc(Pid, Lang, Mod) ->
         set_timeout_fun = {Mod, set_timeout},
         stop_fun = {Mod, stop}
     },
+    unlink(Pid),
     {ok, Proc}.
 
 get_query_server_config() ->
-- 
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