[couchdb] 16/17: FIXUP: Crash the LRU if its evictor dies

[da...@apache.org]

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davisp pushed a commit to branch optimize-ddoc-cache
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit 69dcaa4598b447a6dddcbc3fb9055a43136b01bd
Author: Paul J. Davis <pa...@gmail.com>
AuthorDate: Mon Jul 10 13:24:15 2017 -0500

    FIXUP: Crash the LRU if its evictor dies
    
    The time between the process death and restart is a window where we
    could miss eviction events which would lead to a temporarily inconsitent
    cache. Given that we expect this to happen basically never we'll just
    reuse the restart the world approach to maintaining consistency.
---
 src/ddoc_cache/src/ddoc_cache_lru.erl            |  9 +++------
 src/ddoc_cache/test/ddoc_cache_coverage_test.erl | 18 ++++++++----------
 2 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/src/ddoc_cache/src/ddoc_cache_lru.erl b/src/ddoc_cache/src/ddoc_cache_lru.erl
index 2764959..ff70342 100644
--- a/src/ddoc_cache/src/ddoc_cache_lru.erl
+++ b/src/ddoc_cache/src/ddoc_cache_lru.erl
@@ -89,6 +89,7 @@ init(_) ->
     {ok, Evictor} = couch_event:link_listener(
             ?MODULE, handle_db_event, nil, [all_dbs]
         ),
+    ?EVENT(lru_init, nil),
     {ok, #st{
         pids = Pids,
         dbs = Dbs,
@@ -191,12 +192,8 @@ handle_cast(Msg, St) ->
     {stop, {invalid_cast, Msg}, St}.
 
 
-handle_info({'EXIT', Pid, _Reason}, #st{evictor = Pid} = St) ->
-    ?EVENT(evictor_died, Pid),
-    {ok, Evictor} = couch_event:link_listener(
-            ?MODULE, handle_db_event, nil, [all_dbs]
-        ),
-    {noreply, St#st{evictor=Evictor}};
+handle_info({'EXIT', Pid, Reason}, #st{evictor = Pid} = St) ->
+    {stop, Reason, St};
 
 handle_info({'EXIT', Pid, normal}, St) ->
     % This clause handles when an entry starts
diff --git a/src/ddoc_cache/test/ddoc_cache_coverage_test.erl b/src/ddoc_cache/test/ddoc_cache_coverage_test.erl
index 91182ca..57959f5 100644
--- a/src/ddoc_cache/test/ddoc_cache_coverage_test.erl
+++ b/src/ddoc_cache/test/ddoc_cache_coverage_test.erl
@@ -26,7 +26,7 @@ coverage_test_() ->
         [
             fun restart_lru/0,
             fun restart_tables/0,
-            fun restart_evictor/0
+            fun stop_on_evictor_death/0
         ]
     }.
 
@@ -43,22 +43,20 @@ restart_tables() ->
     ?assertEqual({ok, foo}, ddoc_cache_tables:code_change(1, foo, [])).
 
 
-restart_evictor() ->
+stop_on_evictor_death() ->
     meck:new(ddoc_cache_ev, [passthrough]),
     try
-        State = sys:get_state(ddoc_cache_lru),
+        Lru = whereis(ddoc_cache_lru),
+        State = sys:get_state(Lru),
         Evictor = element(4, State),
-        Ref = erlang:monitor(process, Evictor),
+        Ref = erlang:monitor(process, Lru),
         exit(Evictor, shutdown),
         receive
             {'DOWN', Ref, _, _, Reason} ->
-                couch_log:error("MONITOR: ~p", [Reason]),
-                ok
+                ?assertEqual(shutdown, Reason)
         end,
-        meck:wait(ddoc_cache_ev, event, [evictor_died, '_'], 1000),
-        NewState = sys:get_state(ddoc_cache_lru),
-        NewEvictor = element(4, NewState),
-        ?assertNotEqual(Evictor, NewEvictor)
+        meck:wait(ddoc_cache_ev, event, [lru_init, '_'], 1000),
+        ?assert(whereis(ddoc_cache_lru) /= Lru)
     after
         meck:unload()
     end.

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