Ensure monitors are rebuilt on scope process crash.

src/syn_registry.erl

@@ -153,6 +153,8 @@ count(Scope, Node) ->
 init([Scope, ProcessName]) ->
     %% monitor nodes
     ok = net_kernel:monitor_nodes(true),
+    %% rebuild monitors (if after crash)
+    rebuild_monitors(Scope),
     %% build state
     State = #state{
         scope = Scope,
@@ -335,7 +337,7 @@ handle_info({'DOWN', _MRef, process, Pid, Reason}, #state{scope = Scope} = State
             );
 
         Entries ->
-            lists:foreach(fun({{Name, Pid}, _, _, _, _}) ->
+            lists:foreach(fun({{Name, _Pid}, _, _, _, _}) ->
                 %% remove from table
                 remove_from_local_table(Scope, Name, Pid),
                 %% broadcast
@@ -382,6 +384,21 @@ get_process_name_for_scope(Scope) ->
     ScopeBin = atom_to_binary(Scope),
     binary_to_atom(<<ModuleBin/binary, "_", ScopeBin/binary>>).
 
+-spec rebuild_monitors(Scope :: atom()) -> ok.
+rebuild_monitors(Scope) ->
+    RegistryTuples = get_registry_tuples_for_node(Scope, node()),
+    lists:foreach(fun({Name, Pid, Meta, Time}) ->
+        remove_from_local_table(Scope, Name, Pid),
+        case is_process_alive(Pid) of
+            true ->
+                MRef = erlang:monitor(process, Pid),
+                add_to_local_table(Scope, Name, Pid, Meta, Time, MRef);
+
+            _ ->
+                ok
+        end
+    end, RegistryTuples).
+
 -spec broadcast(Message :: any(), #state{}) -> any().
 broadcast(Message, #state{process_name = ProcessName, nodes = Nodes}) ->
     lists:foreach(fun(RemoteNode) -> gen_server:cast({ProcessName, RemoteNode}, Message) end, maps:keys(Nodes)).
@@ -396,6 +413,14 @@ cast_to_node(RemoteNode, Message, #state{
 }) ->
     gen_server:cast({ProcessName, RemoteNode}, Message).
 
+-spec get_registry_tuples_for_node(Scope :: atom(), Node :: node()) -> [syn_registry_tuple()].
+get_registry_tuples_for_node(Scope, Node) ->
+    ets:select(syn_backbone:get_table_name(syn_registry_by_name, Scope), [{
+        {{'$1', '$2'}, '$3', '$4', '_', Node},
+        [],
+        [{{'$1', '$2', '$3', '$4'}}]
+    }]).
+
 -spec find_registry_entry_by_name(Scope :: atom(), Name :: any()) -> Entry :: syn_registry_entry() | undefined.
 find_registry_entry_by_name(Scope, Name) ->
     case ets:select(syn_backbone:get_table_name(syn_registry_by_name, Scope), [{

test/syn_registry_SUITE.erl

@@ -390,6 +390,10 @@ three_nodes_register_unregister_and_monitor_default_scope(Config) ->
     1 = syn:registry_count(default, SlaveNode1),
     0 = syn:registry_count(default, SlaveNode2),
 
+    %% crash scope process to ensure that monitors get recreated
+    exit(whereis(syn_registry_default), kill),
+    timer:sleep(100), %$ wait for sup to restart it
+
     %% kill process
     syn_test_suite_helper:kill_process(Pid),
     syn_test_suite_helper:kill_process(PidRemoteOn1),
@@ -544,6 +548,10 @@ three_nodes_register_unregister_and_monitor_custom_scope(Config) ->
     {PidWithMeta, <<"with_meta_updated">>} = rpc:call(SlaveNode1, syn, lookup, [custom_scope_ab, "scope_a_alias"]),
     {badrpc, {'EXIT', {{invalid_scope, custom_scope_ab}, _}}} = catch rpc:call(SlaveNode2, syn, lookup, [custom_scope_ab, "scope_a_alias"]),
 
+    %% crash scope process to ensure that monitors get recreated
+    exit(whereis(syn_registry_custom_scope_ab), kill),
+    timer:sleep(100), %$ wait for sup to restart it
+
     %% kill process
     syn_test_suite_helper:kill_process(Pid),
     syn_test_suite_helper:kill_process(PidWithMeta),