rabbit_fifo: release cursor effect ordering

Ensure release cursors are added to the end of the effects list rather
than the front as there may be effects such as log effects that require
log entries that may be truncated by the release cursor effect to be
present.

1 files changed, 3 insertions, 6 deletions

diff --git a/src/rabbit_fifo.erl b/src/rabbit_fifo.erl
index 762963419c..d0b56961ec 100644
--- a/src/rabbit_fifo.erl
+++ b/src/rabbit_fifo.erl
@@ -1103,7 +1103,7 @@ return(#{index := IncomingRaftIdx} = Meta, ConsumerId, Returned,
     {Cons, SQ, Effects2} = update_or_remove_sub(ConsumerId, Con, Cons0,
                                                 SQ0, Effects1),
     State2 = State1#?MODULE{consumers = Cons,
-                           service_queue = SQ},
+                            service_queue = SQ},
     {State, ok, Effects} = checkout(Meta, State2, Effects2),
     update_smallest_raft_index(IncomingRaftIdx, State, Effects).
 
@@ -1153,7 +1153,6 @@ complete_and_checkout(#{index := IncomingRaftIdx} = Meta, MsgIds, ConsumerId,
     {State2, Effects1} = complete(ConsumerId, Discarded, Con0,
                                   Effects0, State0),
     {State, ok, Effects} = checkout(Meta, State2, Effects1),
-    % settle metrics are incremented separately
     update_smallest_raft_index(IncomingRaftIdx, State, Effects).
 
 dead_letter_effects(_Reason, _Discarded,
@@ -1199,8 +1198,7 @@ update_smallest_raft_index(IncomingRaftIdx,
             % we can forward release_cursor all the way until
             % the last received command, hooray
             State = State0#?MODULE{release_cursors = lqueue:new()},
-            {State, ok,
-             [{release_cursor, IncomingRaftIdx, State} | Effects]};
+            {State, ok, Effects ++ [{release_cursor, IncomingRaftIdx, State}]};
         _ ->
             Smallest = rabbit_fifo_index:smallest(Indexes),
             case find_next_cursor(Smallest, Cursors0) of
@@ -1211,7 +1209,7 @@ update_smallest_raft_index(IncomingRaftIdx,
                     %% we can emit a release cursor we've passed the smallest
                     %% release cursor available.
                     {State0#?MODULE{release_cursors = Cursors}, ok,
-                     [Cursor | Effects]}
+                     Effects ++ [Cursor]}
             end
     end.
 
@@ -1315,7 +1313,6 @@ return_all(#?MODULE{consumers = Cons} = State0, Effects0, ConsumerId,
                 end, {State, Effects0}, Checked).
 
 %% checkout new messages to consumers
-%% reverses the effects list
 checkout(#{index := Index}, State0, Effects0) ->
     {State1, _Result, Effects1} = checkout0(checkout_one(State0),
                                             Effects0, {#{}, #{}}),