Assert that index sig never changes in the lifetime of a couch index process

COUCHDB-1444 demonstrates that #st{} state get out of sync
somehow, leading to unexpected 404's (missing_named_view) and
200's. This patch ensures that index sig never changes in the hope
that it will lead to the cause of 1444 and prevent other occurrences
of the same class of bug.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/couch_index/src/couch_index.erl b/src/couch_index/src/couch_index.erl
index 508604829..5bf322e9f 100644
--- a/src/couch_index/src/couch_index.erl
+++ b/src/couch_index/src/couch_index.erl
@@ -171,6 +171,7 @@ handle_call({compacted, NewIdxState}, _From, State) ->
         updater=Updater,
         commit_delay=Delay
     } = State,
+    assert_signature_match(Mod, OldIdxState, NewIdxState),
     NewSeq = Mod:get(update_seq, NewIdxState),
     OldSeq = Mod:get(update_seq, OldIdxState),
     % For indices that require swapping files, we have to make sure we're
@@ -210,7 +211,12 @@ handle_cast({updated, NewIdxState}, State) ->
             {noreply, NewState}
     end;
 handle_cast({new_state, NewIdxState}, State) ->
-    #st{mod=Mod, commit_delay=Delay} = State,
+    #st{
+        mod=Mod,
+        idx_state=OldIdxState,
+        commit_delay=Delay
+    } = State,
+    assert_signature_match(Mod, OldIdxState, NewIdxState),
     CurrSeq = Mod:get(update_seq, NewIdxState),
     Args = [
         Mod:get(db_name, NewIdxState),
@@ -323,3 +329,9 @@ send_replies(Waiters, UpdateSeq, IdxState) ->
     {ToSend, Remaining} = lists:partition(Pred, Waiters),
     [gen_server:reply(From, {ok, IdxState}) || {From, _} <- ToSend],
     Remaining.
+
+assert_signature_match(Mod, OldIdxState, NewIdxState) ->
+    case {Mod:get(signature, OldIdxState), Mod:get(signature, NewIdxState)} of
+        {Sig, Sig} -> ok;
+        _ -> erlang:error(signature_mismatch)
+    end.