Merge pull request #59 from dziaineka/fix-premature-demonitor

Fix premature demonitor

src/syn_registry.erl

@@ -500,8 +500,8 @@ unregister_on_node(Name) ->
             {error, undefined};
 
         {{Name, Pid}, _Meta, _Clock, MonitorRef, _Node} when MonitorRef =/= undefined ->
-            %% demonitor
-            erlang:demonitor(MonitorRef, [flush]),
+            %% demonitor if it is last name to unregister for the Pid
+            maybe_demonitor(Pid),
             %% remove from table
             remove_from_local_table(Name, Pid),
             %% return
@@ -527,6 +527,22 @@ unregister_on_node(Name) ->
             {error, remote_pid}
     end.
 
+-spec maybe_demonitor(Pid :: pid()) -> ok.
+maybe_demonitor(Pid) ->
+    %% try to get two items to check if it only one item left
+    case ets:select(syn_registry_by_pid, [{
+        {{Pid, '_'}, '_', '_', '$5', '_'},
+        [],
+        ['$5']
+    }], 2) of
+        {[MonitorRef], _} ->
+            erlang:demonitor(MonitorRef, [flush]),
+            ok;
+
+        _ ->
+            ok
+    end.
+
 -spec add_to_local_table(
     Name :: any(),
     Pid :: pid(),

test/syn_registry_SUITE.erl

@@ -35,6 +35,7 @@
 -export([
     single_node_register_and_monitor/1,
     single_node_register_and_unregister/1,
+    single_node_register_unregister_and_kill_process/1,
     single_node_registration_errors/1,
     single_node_registry_count/1,
     single_node_register_gen_server/1,
@@ -112,6 +113,7 @@ groups() ->
         {single_node_process_registration, [shuffle], [
             single_node_register_and_monitor,
             single_node_register_and_unregister,
+            single_node_register_unregister_and_kill_process,
             single_node_registration_errors,
             single_node_registry_count,
             single_node_register_gen_server,
@@ -283,6 +285,25 @@ single_node_register_and_unregister(_Config) ->
     undefined = syn:whereis(<<"my proc">>),
     undefined = syn:whereis(<<"my proc 2">>).
 
+single_node_register_unregister_and_kill_process(_Config) ->
+    %% start
+    ok = syn:start(),
+    %% start process
+    Pid = syn_test_suite_helper:start_process(),
+    %% register
+    ok = syn:register(<<"synonym_to_unregister">>, Pid),
+    ok = syn:register(<<"synonym_to_keep">>, Pid),
+    %% unregister
+    ok = syn:unregister(<<"synonym_to_unregister">>),
+    %% retrieve
+    undefined = syn:whereis(<<"synonym_to_unregister">>),
+    Pid = syn:whereis(<<"synonym_to_keep">>),
+    %% kill process
+    true = syn_test_suite_helper:kill_process(Pid),
+    timer:sleep(100),
+    %% retrieve
+    undefined = syn:whereis(<<"synonym_to_keep">>).
+
 single_node_registration_errors(_Config) ->
     %% start
     ok = syn:start(),