[couchdb] 01/01: FIXUP: Process processes in the process of dying

[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 ee00280fea0698fa30cab2bd78f0818dc67cee42
Author: Paul J. Davis <pa...@gmail.com>
AuthorDate: Thu Jul 20 14:02:57 2017 -0500

    FIXUP: Process processes in the process of dying
    
    Turns out we could go to evict an entry just after it had decided to
    leave the cache (i.e., its ddoc was just deleted). When that happens
    ddoc_cache_lru would die trying to shut the process down becuase the
    process died normal earlier than expected.
---
 src/ddoc_cache/src/ddoc_cache_entry.erl       | 20 +++++++++++++++-----
 src/ddoc_cache/test/ddoc_cache_entry_test.erl | 17 +++++++++++++++++
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/src/ddoc_cache/src/ddoc_cache_entry.erl b/src/ddoc_cache/src/ddoc_cache_entry.erl
index 63a2efa..77539eb 100644
--- a/src/ddoc_cache/src/ddoc_cache_entry.erl
+++ b/src/ddoc_cache/src/ddoc_cache_entry.erl
@@ -77,7 +77,17 @@ start_link(Key, Default) ->
 
 
 shutdown(Pid) ->
-    ok = gen_server:call(Pid, shutdown).
+    Ref = erlang:monitor(process, Pid),
+    ok = gen_server:cast(Pid, shutdown),
+    receive
+        {'DOWN', Ref, process, Pid, normal} ->
+            ok;
+        {'DOWN', Ref, process, Pid, Reason} ->
+            erlang:exit(Reason)
+    after ?SHUTDOWN_TIMEOUT ->
+        erlang:demonitor(Ref, [flush]),
+        erlang:exit({timeout, {entry_shutdown, Pid}})
+    end.
 
 
 open(Pid, Key) ->
@@ -170,10 +180,6 @@ handle_call(open, From, #st{opener = Pid} = St) when is_pid(Pid) ->
 handle_call(open, _From, St) ->
     {reply, St#st.val, St};
 
-handle_call(shutdown, _From, St) ->
-    remove_from_cache(St),
-    {stop, normal, ok, St};
-
 handle_call(Msg, _From, St) ->
     {stop, {bad_call, Msg}, {bad_call, Msg}, St}.
 
@@ -227,6 +233,10 @@ handle_cast(refresh, #st{opener = Pid} = St) when is_pid(Pid) ->
     },
     {noreply, NewSt};
 
+handle_cast(shutdown, St) ->
+    remove_from_cache(St),
+    {stop, normal, St};
+
 handle_cast(Msg, St) ->
     {stop, {bad_cast, Msg}, St}.
 
diff --git a/src/ddoc_cache/test/ddoc_cache_entry_test.erl b/src/ddoc_cache/test/ddoc_cache_entry_test.erl
index 381185c..c481bcf 100644
--- a/src/ddoc_cache/test/ddoc_cache_entry_test.erl
+++ b/src/ddoc_cache/test/ddoc_cache_entry_test.erl
@@ -52,6 +52,7 @@ check_entry_test_() ->
             fun kill_opener_on_terminate/1,
             fun evict_when_not_accessed/1,
             fun open_dead_entry/1,
+            fun handles_bad_shutdown/1,
             fun handles_bad_messages/1,
             fun handles_code_change/1
         ]}
@@ -125,6 +126,22 @@ open_dead_entry({DbName, _}) ->
     ?assertEqual(recover(DbName), ddoc_cache_entry:open(Pid, Key)).
 
 
+handles_bad_shutdown(_) ->
+    ErrorPid = spawn(fun() ->
+        receive
+           _ -> exit(bad_shutdown)
+        end
+    end),
+    ?assertExit(bad_shutdown, ddoc_cache_entry:shutdown(ErrorPid)),
+    NotDeadYetPid = spawn(fun() ->
+        timer:sleep(infinity)
+    end),
+    ?assertExit(
+            {timeout, {entry_shutdown, NotDeadYetPid}},
+            ddoc_cache_entry:shutdown(NotDeadYetPid)
+        ).
+
+
 handles_bad_messages(_) ->
     CallExpect = {stop, {bad_call, foo}, {bad_call, foo}, baz},
     CastExpect = {stop, {bad_cast, foo}, bar},

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