ejabberd document NOT updated : IQ Handler discipline

[AobaIwaki123]

About

I read about IQ descipline to understand IQ handler
It says IQ handler supports parallel execution
However it's deprecated from gen_iq_handler.erl in master branch

Question

I want to know how to make IQ handler parallel

[badlop]

Right, that was deprecated in ejabberd 18.03. The commit message explains it.

And right, that paragraph in the documentation is obsolete ans should be removed.

Thanks for reporting it!

[AobaIwaki123]

Thank you for reply!
Anyway, is it possible to execute iq handler in parallel?

[badlop]

Update: No need to do anything, iq queries are handled in parallel already.

I applied the patch (1) to confirm that IQ queries are processed in parallel.

This patch adds a 10 seconds delay to IQ disco-features queries sent by user1; other users have no delay.

When user1 sends a query, he has to wait 10 seconds to receive the response from ejabberd; in the meantime, any other user can send similar queries and they are processed immediately, without waiting for user1:

# user1 sends query but doesn't yet receive the response:
2024-09-02 10:28:30.698067+02:00 [info] mod_disco proces_local_iq_info start <<"user1">>
2024-09-02 10:28:30.698225+02:00 [info] mod_announce disco features start <<"user1">>

# admin sends query and receives the response immediately:
2024-09-02 10:28:33.654562+02:00 [info] mod_disco proces_local_iq_info start <<"admin">>
2024-09-02 10:28:33.654704+02:00 [info] mod_announce disco features start <<"admin">>
2024-09-02 10:28:33.654854+02:00 [info] mod_announce disco features result <<"admin">>
2024-09-02 10:28:33.655111+02:00 [info] mod_disco proces_local_iq_info result <<"admin">>

# user1 finall receives the response:
2024-09-02 10:28:40.698818+02:00 [info] mod_announce disco features result <<"user1">>
2024-09-02 10:28:40.699266+02:00 [info] mod_disco proces_local_iq_info result <<"user1">>

(1) Patch for ejabberd git:

diff --git a/src/mod_announce.erl b/src/mod_announce.erl
index d7f983716..9aca6cd8d 100644
--- a/src/mod_announce.erl
+++ b/src/mod_announce.erl
@@ -262,6 +262,7 @@ disco_features(Acc, From, #jid{lserver = LServer} = _To, <<"announce">>, Lang) -
     end;
 
 disco_features(Acc, From, #jid{lserver = LServer} = _To, Node, Lang) ->
+    ?INFO_MSG("mod_announce disco features start ~p", [From#jid.luser]),
     case gen_mod:is_loaded(LServer, mod_adhoc) of
 	false ->
 	    Acc;
@@ -270,6 +271,11 @@ disco_features(Acc, From, #jid{lserver = LServer} = _To, Node, Lang) ->
 	    Allow = acl:match_rule(LServer, Access, From),
 	    AccessGlobal = get_access(global),
 	    AllowGlobal = acl:match_rule(global, AccessGlobal, From),
+            case From#jid.luser of
+                <<"user1">> -> timer:sleep(10000);
+                _ -> ok
+            end,
+            ?INFO_MSG("mod_announce disco features result ~p", [From#jid.luser]),
 	    case Node of
 		?NS_ADMIN_ANNOUNCE ->
 		    ?INFO_RESULT(Allow, [?NS_COMMANDS], Lang);
diff --git a/src/mod_disco.erl b/src/mod_disco.erl
index 4f092da4e..f1248b3f2 100644
--- a/src/mod_disco.erl
+++ b/src/mod_disco.erl
@@ -119,6 +119,7 @@ process_local_iq_info(#iq{type = set, lang = Lang} = IQ) ->
 process_local_iq_info(#iq{type = get, lang = Lang,
 			  from = From, to = To,
 			  sub_els = [#disco_info{node = Node}]} = IQ) ->
+    ?INFO_MSG("mod_disco proces_local_iq_info start ~p", [From#jid.luser]),
     Host = To#jid.lserver,
     Identity = ejabberd_hooks:run_fold(disco_local_identity,
 				       Host, [], [From, To, Node, Lang]),
@@ -127,6 +128,7 @@ process_local_iq_info(#iq{type = get, lang = Lang,
     case ejabberd_hooks:run_fold(disco_local_features, Host,
 				 empty, [From, To, Node, Lang]) of
 	{result, Features} ->
+            ?INFO_MSG("mod_disco proces_local_iq_info result ~p", [From#jid.luser]),
 	    xmpp:make_iq_result(IQ, #disco_info{node = Node,
 						identities = Identity,
 						xdata = Info,