Share the exchange scratch space

3 files changed, 44 insertions, 11 deletions

diff --git a/include/rabbit.hrl b/include/rabbit.hrl
index 5c73c8b88b..8de31490c8 100644
--- a/include/rabbit.hrl
+++ b/include/rabbit.hrl
@@ -43,7 +43,7 @@
 -record(resource, {virtual_host, kind, name}).
 
 -record(exchange, {name, type, durable, auto_delete, internal, arguments,
-                   scratch}).
+                   scratches}).
 -record(exchange_serial, {name, next}).
 
 -record(amqqueue, {name, durable, auto_delete, exclusive_owner = none,
diff --git a/src/rabbit_exchange.erl b/src/rabbit_exchange.erl
index ac2f26108f..7455c797e3 100644
--- a/src/rabbit_exchange.erl
+++ b/src/rabbit_exchange.erl
@@ -20,7 +20,7 @@
 
 -export([recover/0, callback/4, declare/6,
          assert_equivalence/6, assert_args_equivalence/2, check_type/1,
-         lookup/1, lookup_or_die/1, list/1, lookup_scratch/1,  update_scratch/2,
+         lookup/1, lookup_or_die/1, list/1, lookup_scratch/2, update_scratch/3,
          info_keys/0, info/1, info/2, info_all/1, info_all/2,
          route/2, delete/2]).
 %% these must be run inside a mnesia tx
@@ -60,10 +60,10 @@
         (name()) -> rabbit_types:exchange() |
                     rabbit_types:channel_exit()).
 -spec(list/1 :: (rabbit_types:vhost()) -> [rabbit_types:exchange()]).
--spec(lookup_scratch/1 :: (name()) ->
+-spec(lookup_scratch/2 :: (name(), atom()) ->
                                rabbit_types:ok(term()) |
                                rabbit_types:error('not_found')).
--spec(update_scratch/2 :: (name(), fun((any()) -> any())) -> 'ok').
+-spec(update_scratch/3 :: (name(), atom(), fun((any()) -> any())) -> 'ok').
 -spec(info_keys/0 :: () -> rabbit_types:info_keys()).
 -spec(info/1 :: (rabbit_types:exchange()) -> rabbit_types:infos()).
 -spec(info/2 ::
@@ -108,7 +108,6 @@ recover() ->
 
 callback(X = #exchange{type = XType}, Fun, Serial0, Args) ->
     %% TODO cache this?
-    %% TODO what about sharing the scratch space?
     Serial = fun (Bool) ->
                      case Serial0 of
                          _ when is_atom(Serial0) -> Serial0;
@@ -237,18 +236,34 @@ list(VHostPath) ->
       rabbit_exchange,
       #exchange{name = rabbit_misc:r(VHostPath, exchange), _ = '_'}).
 
-lookup_scratch(Name) ->
+lookup_scratch(Name, App) ->
     case lookup(Name) of
-        {ok, #exchange{scratch = Scratch}} -> {ok, Scratch};
-        {error, not_found}                 -> {error, not_found}
+        {ok, #exchange{scratches = undefined}} ->
+            {error, not_found};
+        {ok, #exchange{scratches = Scratches}} ->
+            case orddict:find(App, Scratches) of
+                {ok, Value} -> {ok, Value};
+                error       -> {error, not_found}
+            end;
+        {error, not_found} ->
+            {error, not_found}
     end.
 
-update_scratch(Name, Fun) ->
+update_scratch(Name, App, Fun) ->
     rabbit_misc:execute_mnesia_transaction(
       fun() ->
               case mnesia:wread({rabbit_exchange, Name}) of
-                  [X = #exchange{durable = Durable, scratch = Scratch}] ->
-                      X1 = X#exchange{scratch = Fun(Scratch)},
+                  [X = #exchange{durable = Durable, scratches = Scratches0}] ->
+                      Scratches1 = case Scratches0 of
+                                       undefined -> orddict:new();
+                                       _         -> Scratches0
+                                   end,
+                      Scratch = case orddict:find(App, Scratches1) of
+                                    {ok, S} -> S;
+                                    error   -> undefined
+                                end,
+                      Scratches2 = orddict:store(App, Fun(Scratch), Scratches1),
+                      X1 = X#exchange{scratches = Scratches2},
                       ok = mnesia:write(rabbit_exchange, X1, write),
                       case Durable of
                           true -> ok = mnesia:write(rabbit_durable_exchange,
diff --git a/src/rabbit_upgrade_functions.erl b/src/rabbit_upgrade_functions.erl
index 485ccc5f02..87e560e869 100644
--- a/src/rabbit_upgrade_functions.erl
+++ b/src/rabbit_upgrade_functions.erl
@@ -37,6 +37,7 @@
 -rabbit_upgrade({mirrored_supervisor,   mnesia, []}).
 -rabbit_upgrade({topic_trie_node,       mnesia, []}).
 -rabbit_upgrade({runtime_parameters,    mnesia, []}).
+-rabbit_upgrade({exchange_scratches,    mnesia, [exchange_scratch]}).
 
 %% -------------------------------------------------------------------
 
@@ -193,6 +194,23 @@ runtime_parameters() ->
             {attributes, [key, value]},
             {disc_copies, [node()]}]).
 
+exchange_scratches() ->
+    ok = exchange_scratches(rabbit_exchange),
+    ok = exchange_scratches(rabbit_durable_exchange).
+
+exchange_scratches(Table) ->
+    transform(
+      Table,
+      fun ({exchange, Name, Type = <<"x-federation">>, Dur, AutoDel, Int, Args,
+            Scratch}) ->
+              Scratches = orddict:store(federation, Scratch, orddict:new()),
+              {exchange, Name, Type, Dur, AutoDel, Int, Args, Scratches};
+          %% We assert here that nothing else uses the scratch mechanism ATM
+          ({exchange, Name, Type, Dur, AutoDel, Int, Args, undefined}) ->
+              {exchange, Name, Type, Dur, AutoDel, Int, Args, undefined}
+      end,
+      [name, type, durable, auto_delete, internal, arguments, scratches]).
+
 %%--------------------------------------------------------------------
 
 transform(TableName, Fun, FieldList) ->