Refactor OS process management

Squashed commit of the following:
commit a9cd9681f6c88f0f3c019e98e2edfef55cad0129
commit eb38bca08ffbf778b69fbb2d612e23733af82ff5
commit 98a03a079ab24f2c7bd9e0d6d7fac5fa62bfd4eb
commit 9b8ec059165d981e4cd743008ecdf393a4f37f61
commit 3a891c1dd9a17fdd267c423b340dd09c31c89d7a
commit 68351dd181c8a92b5baa9ac23f25c7c191484394
commit e4384a517e2efeac9231701898a6c67213642319
commit cd954661422d0ef146b5bd7792f835dcc4220c84
commit 3bcca92c7c0102d5722dfc6b2c332766cfe0370c
commit 82d15f40f503b2609cf785ce2837e1280edaaa43
commit 70051abbd699e076452d772587c32ee5e09bdcbc
commit 7f01d37781e7774015f6cb34f795b28db9ecc9f5

BugzID: 11572

See also COUCHDB-901

A new config setting is introduced.  The following block controls the
maximum number of OS processes that will be reused.  Additional OS
processes will still be spawned on-demand, but they'll be terminated
when the clients are through with them.

[query_server_config]
os_process_soft_limit = 100

1 files changed, 3 insertions, 211 deletions

diff --git a/apps/couch/src/couch_query_servers.erl b/apps/couch/src/couch_query_servers.erl
index a4850e86..4e86dcf4 100644
--- a/apps/couch/src/couch_query_servers.erl
+++ b/apps/couch/src/couch_query_servers.erl
@@ -11,11 +11,7 @@
 % the License.
 
 -module(couch_query_servers).
--behaviour(gen_server).
 
--export([start_link/0, config_change/1]).
-
--export([init/1, terminate/2, handle_call/3, handle_cast/2, handle_info/2,code_change/3]).
 -export([start_doc_map/2, map_docs/2, stop_doc_map/1]).
 -export([reduce/3, rereduce/3,validate_doc_update/5]).
 -export([filter_docs/5]).
@@ -27,18 +23,6 @@
 
 -include("couch_db.hrl").
 
--record(proc, {
-    pid,
-    lang,
-    ddoc_keys = [],
-    prompt_fun,
-    set_timeout_fun,
-    stop_fun
-}).
-
-start_link() ->
-    gen_server:start_link({local, couch_query_servers}, couch_query_servers, [], []).
-
 start_doc_map(Lang, Functions) ->
     Proc = get_os_process(Lang),
     lists:foreach(fun(FunctionSource) ->
@@ -223,151 +207,6 @@ with_ddoc_proc(#doc{id=DDocId,revs={Start, [DiskRev|_]}}=DDoc, Fun) ->
         ok = ret_os_process(Proc)
     end.
 
-init([]) ->
-    % register async to avoid deadlock on restart_child
-    Self = self(),
-    spawn(couch_config, register, [fun ?MODULE:config_change/1, Self]),
-
-    Langs = ets:new(couch_query_server_langs, [set, private]),
-    PidProcs = ets:new(couch_query_server_pid_langs, [set, private]),
-    LangProcs = ets:new(couch_query_server_procs, [set, private]),
-    % 'query_servers' specifies an OS command-line to execute.
-    lists:foreach(fun({Lang, Command}) ->
-        true = ets:insert(Langs, {?l2b(Lang),
-                          couch_os_process, start_link, [Command]})
-    end, couch_config:get("query_servers")),
-    % 'native_query_servers' specifies a {Module, Func, Arg} tuple.
-    lists:foreach(fun({Lang, SpecStr}) ->
-        {ok, {Mod, Fun, SpecArg}} = couch_util:parse_term(SpecStr),
-        true = ets:insert(Langs, {?l2b(Lang),
-                          Mod, Fun, SpecArg})
-    end, couch_config:get("native_query_servers")),
-    process_flag(trap_exit, true),
-    {ok, {Langs, % Keyed by language name, value is {Mod,Func,Arg}
-          PidProcs, % Keyed by PID, valus is a #proc record.
-          LangProcs % Keyed by language name, value is a #proc record
-          }}.
-
-terminate(_Reason, {_Langs, PidProcs, _LangProcs}) ->
-    [couch_util:shutdown_sync(P) || {P,_} <- ets:tab2list(PidProcs)],
-    ok.
-
-handle_call({get_proc, #doc{body={Props}}=DDoc, DDocKey}, _From, {Langs, PidProcs, LangProcs}=Server) ->
-    % Note to future self. Add max process limit.
-    Lang = couch_util:get_value(<<"language">>, Props, <<"javascript">>),
-    case ets:lookup(LangProcs, Lang) of
-    [{Lang, [P|Rest]}] ->
-        % find a proc in the set that has the DDoc
-        {ok, Proc} = proc_with_ddoc(DDoc, DDocKey, [P|Rest]),
-        rem_from_list(LangProcs, Lang, Proc),
-        {reply, {ok, Proc, get_query_server_config()}, Server};
-    _ ->
-        case (catch new_process(Langs, Lang)) of
-        {ok, Proc} ->
-            add_value(PidProcs, Proc#proc.pid, Proc),
-            {ok, Proc2} = proc_with_ddoc(DDoc, DDocKey, [Proc]),
-            {reply, {ok, Proc2, get_query_server_config()}, Server};
-        Error ->
-            {reply, Error, Server}
-        end
-    end;
-handle_call({get_proc, Lang}, _From, {Langs, PidProcs, LangProcs}=Server) ->
-    % Note to future self. Add max process limit.
-    case ets:lookup(LangProcs, Lang) of
-    [{Lang, [Proc|_]}] ->
-        rem_from_list(LangProcs, Lang, Proc),
-        {reply, {ok, Proc, get_query_server_config()}, Server};
-    _ ->
-        case (catch new_process(Langs, Lang)) of
-        {ok, Proc} ->
-            add_value(PidProcs, Proc#proc.pid, Proc),
-            {reply, {ok, Proc, get_query_server_config()}, Server};
-        Error ->
-            {reply, Error, Server}
-        end
-    end;
-handle_call({unlink_proc, Pid}, _From, {_, PidProcs, _}=Server) ->
-    rem_value(PidProcs, Pid),
-    unlink(Pid),
-    {reply, ok, Server};
-handle_call({ret_proc, Proc}, _From, {_, PidProcs, LangProcs}=Server) ->
-    % Along with max process limit, here we should check
-    % if we're over the limit and discard when we are.
-    add_value(PidProcs, Proc#proc.pid, Proc),
-    add_to_list(LangProcs, Proc#proc.lang, Proc),
-    link(Proc#proc.pid),
-    {reply, true, Server}.
-
-handle_cast(_Whatever, Server) ->
-    {noreply, Server}.
-
-handle_info({'EXIT', Pid, Status}, {_, PidProcs, LangProcs}=Server) ->
-    case ets:lookup(PidProcs, Pid) of
-    [{Pid, Proc}] ->
-        case Status of
-        normal -> ok;
-        _ -> ?LOG_DEBUG("Linked process died abnormally: ~p (reason: ~p)", [Pid, Status])
-        end,
-        rem_value(PidProcs, Pid),
-        catch rem_from_list(LangProcs, Proc#proc.lang, Proc),
-        {noreply, Server};
-    [] ->
-        case Status of
-        normal ->
-            {noreply, Server};
-        _ ->
-            {stop, Status, Server}
-        end
-    end.
-
-code_change(_OldVsn, State, _Extra) ->
-    {ok, State}.
-
-config_change("query_servers") ->
-    supervisor:terminate_child(couch_secondary_services, query_servers),
-    supervisor:restart_child(couch_secondary_services, query_servers);
-config_change("native_query_servers") ->
-    supervisor:terminate_child(couch_secondary_services, query_servers),
-    supervisor:restart_child(couch_secondary_services, query_servers).
-
-% Private API
-
-get_query_server_config() ->
-    ReduceLimit = list_to_atom(
-        couch_config:get("query_server_config","reduce_limit","true")),
-    {[{<<"reduce_limit">>, ReduceLimit}]}.
-
-new_process(Langs, Lang) ->
-    case ets:lookup(Langs, Lang) of
-    [{Lang, Mod, Func, Arg}] ->
-        {ok, Pid} = apply(Mod, Func, Arg),
-        {ok, #proc{lang=Lang,
-                   pid=Pid,
-                   % Called via proc_prompt, proc_set_timeout, and proc_stop
-                   prompt_fun={Mod, prompt},
-                   set_timeout_fun={Mod, set_timeout},
-                   stop_fun={Mod, stop}}};
-    _ ->
-        {unknown_query_language, Lang}
-    end.
-
-proc_with_ddoc(DDoc, DDocKey, LangProcs) ->
-    DDocProcs = lists:filter(fun(#proc{ddoc_keys=Keys}) ->
-            lists:any(fun(Key) ->
-                Key == DDocKey
-            end, Keys)
-        end, LangProcs),
-    case DDocProcs of
-        [DDocProc|_] ->
-            ?LOG_DEBUG("DDocProc found for DDocKey: ~p",[DDocKey]),
-            {ok, DDocProc};
-        [] ->
-            [TeachProc|_] = LangProcs,
-            ?LOG_DEBUG("Teach ddoc to new proc ~p with DDocKey: ~p",[TeachProc, DDocKey]),
-            {ok, SmartProc} = teach_ddoc(DDoc, DDocKey, TeachProc),
-            {ok, SmartProc}
-    end.
-
 proc_prompt(Proc, Args) ->
     {Mod, Func} = Proc#proc.prompt_fun,
     apply(Mod, Func, [Proc#proc.pid, Args]).
@@ -380,28 +219,15 @@ proc_set_timeout(Proc, Timeout) ->
     {Mod, Func} = Proc#proc.set_timeout_fun,
     apply(Mod, Func, [Proc#proc.pid, Timeout]).
 
-teach_ddoc(DDoc, {DDocId, _Rev}=DDocKey, #proc{ddoc_keys=Keys}=Proc) ->
-    % send ddoc over the wire
-    % we only share the rev with the client we know to update code
-    % but it only keeps the latest copy, per each ddoc, around.
-    true = proc_prompt(Proc, [<<"ddoc">>, <<"new">>, DDocId, couch_doc:to_json_obj(DDoc, [])]),
-    % we should remove any other ddocs keys for this docid
-    % because the query server overwrites without the rev
-    Keys2 = [{D,R} || {D,R} <- Keys, D /= DDocId],
-    % add ddoc to the proc
-    {ok, Proc#proc{ddoc_keys=[DDocKey|Keys2]}}.
-
 get_ddoc_process(#doc{} = DDoc, DDocKey) ->
     % remove this case statement
-    case gen_server:call(couch_query_servers, {get_proc, DDoc, DDocKey}) of
+    case gen_server:call(couch_proc_manager, {get_proc, DDoc, DDocKey}) of
     {ok, Proc, QueryConfig} ->
         % process knows the ddoc
         case (catch proc_prompt(Proc, [<<"reset">>, QueryConfig])) of
         true ->
             proc_set_timeout(Proc, list_to_integer(couch_config:get(
                                 "couchdb", "os_process_timeout", "5000"))),
-            link(Proc#proc.pid),
-            gen_server:call(couch_query_servers, {unlink_proc, Proc#proc.pid}),
             Proc;
         _ ->
             catch proc_stop(Proc),
@@ -412,14 +238,12 @@ get_ddoc_process(#doc{} = DDoc, DDocKey) ->
     end.
 
 get_os_process(Lang) ->
-    case gen_server:call(couch_query_servers, {get_proc, Lang}) of
+    case gen_server:call(couch_proc_manager, {get_proc, Lang}) of
     {ok, Proc, QueryConfig} ->
         case (catch proc_prompt(Proc, [<<"reset">>, QueryConfig])) of
         true ->
             proc_set_timeout(Proc, list_to_integer(couch_config:get(
                                 "couchdb", "os_process_timeout", "5000"))),
-            link(Proc#proc.pid),
-            gen_server:call(couch_query_servers, {unlink_proc, Proc#proc.pid}),
             Proc;
         _ ->
             catch proc_stop(Proc),
@@ -430,38 +254,6 @@ get_os_process(Lang) ->
     end.
 
 ret_os_process(Proc) ->
-    true = gen_server:call(couch_query_servers, {ret_proc, Proc}),
+    true = gen_server:call(couch_proc_manager, {ret_proc, Proc}),
     catch unlink(Proc#proc.pid),
     ok.
-
-add_value(Tid, Key, Value) ->
-    true = ets:insert(Tid, {Key, Value}).
-
-rem_value(Tid, Key) ->
-    true = ets:delete(Tid, Key).
-
-add_to_list(Tid, Key, Value) ->
-    case ets:lookup(Tid, Key) of
-    [{Key, Vals}] ->
-        true = ets:insert(Tid, {Key, [Value|Vals]});
-    [] ->
-        true = ets:insert(Tid, {Key, [Value]})
-    end.
-
-rem_from_list(Tid, Key, Value) when is_record(Value, proc)->
-    Pid = Value#proc.pid,
-    case ets:lookup(Tid, Key) of
-    [{Key, Vals}] ->
-        % make a new values list that doesn't include the Value arg
-        NewValues = [Val || #proc{pid=P}=Val <- Vals, P /= Pid],
-        ets:insert(Tid, {Key, NewValues});
-    [] -> ok
-    end;
-rem_from_list(Tid, Key, Value) ->
-    case ets:lookup(Tid, Key) of
-    [{Key, Vals}] ->
-        % make a new values list that doesn't include the Value arg
-        NewValues = [Val || Val <- Vals, Val /= Value],
-        ets:insert(Tid, {Key, NewValues});
-    [] -> ok
-    end.