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Fix race condition causing stale pids in syn lookup #87

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Fix race condition causing stale pids in syn lookup #87

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25 changes: 22 additions & 3 deletions src/syn_pg.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -419,13 +419,32 @@ handle_call(Request, From, #state{scope = Scope} = State) ->
{noreply, #state{}} |
{noreply, #state{}, timeout() | hibernate | {continue, term()}} |
{stop, Reason :: term(), #state{}}.
%% New format with RemoteScopePid - allows inline discovery
handle_info({'3.0', sync_join, GroupName, Pid, Meta, Time, Reason, RemoteScopePid}, #state{nodes_map = NodesMap} = State) ->
RemoteNode = node(Pid),
case maps:is_key(RemoteNode, NodesMap) of
true ->
handle_pg_sync(GroupName, Pid, Meta, Time, Reason, State),
{noreply, State};

false ->
%% Node not in nodes_map yet - sync arrived before ack_sync due to
%% different sender processes (multicast_loop vs gen_server).
%% Inline the discovery: set up monitor and add to nodes_map.
_MRef = monitor(process, RemoteScopePid),
NodesMap1 = NodesMap#{RemoteNode => RemoteScopePid},
handle_pg_sync(GroupName, Pid, Meta, Time, Reason, State#state{nodes_map = NodesMap1}),
{noreply, State#state{nodes_map = NodesMap1}}
end;

%% Old format for backwards compatibility (rolling upgrades)
handle_info({'3.0', sync_join, GroupName, Pid, Meta, Time, Reason}, #state{nodes_map = NodesMap} = State) ->
case maps:is_key(node(Pid), NodesMap) of
true ->
handle_pg_sync(GroupName, Pid, Meta, Time, Reason, State);

false ->
%% ignore, race condition
%% ignore, cannot inline discover without RemoteScopePid
ok
end,
{noreply, State};
Expand Down Expand Up @@ -573,8 +592,8 @@ do_join_on_node(GroupName, Pid, PreviousMeta, Meta, MRef, Reason, RequesterNode,
%% callback
syn_event_handler:call_event_handler(CallbackMethod, [Scope, GroupName, Pid, Meta, Reason]),
syn_event_handler:call_event_handler(CallbackMethod, [Scope, GroupName, Pid, PreviousMeta, Meta, normal]),
%% broadcast
syn_gen_scope:broadcast({'3.0', sync_join, GroupName, Pid, Meta, Time, Reason}, [RequesterNode], State),
%% broadcast (include self() so receiver can set up monitor if needed)
syn_gen_scope:broadcast({'3.0', sync_join, GroupName, Pid, Meta, Time, Reason, self()}, [RequesterNode], State),
%% return
{reply, {ok, {CallbackMethod, PreviousMeta, Meta, Time, TableByName, TableByPid}}, State}.

Expand Down
27 changes: 23 additions & 4 deletions src/syn_registry.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -314,13 +314,32 @@ handle_call(Request, From, #state{scope = Scope} = State) ->
{noreply, #state{}} |
{noreply, #state{}, timeout() | hibernate | {continue, term()}} |
{stop, Reason :: term(), #state{}}.
%% New format with RemoteScopePid - allows inline discovery
handle_info({'3.0', sync_register, Name, Pid, Meta, Time, Reason, RemoteScopePid}, #state{nodes_map = NodesMap} = State) ->
RemoteNode = node(Pid),
case maps:is_key(RemoteNode, NodesMap) of
true ->
handle_registry_sync(Name, Pid, Meta, Time, Reason, State),
{noreply, State};

false ->
%% Node not in nodes_map yet - sync arrived before ack_sync due to
%% different sender processes (multicast_loop vs gen_server).
%% Inline the discovery: set up monitor and add to nodes_map.
_MRef = monitor(process, RemoteScopePid),
NodesMap1 = NodesMap#{RemoteNode => RemoteScopePid},
handle_registry_sync(Name, Pid, Meta, Time, Reason, State#state{nodes_map = NodesMap1}),
{noreply, State#state{nodes_map = NodesMap1}}
end;

%% Old format for backwards compatibility (rolling upgrades)
handle_info({'3.0', sync_register, Name, Pid, Meta, Time, Reason}, #state{nodes_map = NodesMap} = State) ->
case maps:is_key(node(Pid), NodesMap) of
true ->
handle_registry_sync(Name, Pid, Meta, Time, Reason, State);

false ->
%% ignore, race condition
%% ignore, cannot inline discover without RemoteScopePid
ok
end,
{noreply, State};
Expand Down Expand Up @@ -467,8 +486,8 @@ do_register_on_node(Name, Pid, PreviousMeta, Meta, MRef, Reason, RequesterNode,
%% callback
syn_event_handler:call_event_handler(CallbackMethod, [Scope, Name, Pid, Meta, Reason]),
syn_event_handler:call_event_handler(CallbackMethod, [Scope, Name, Pid, PreviousMeta, Meta, normal]),
%% broadcast
syn_gen_scope:broadcast({'3.0', sync_register, Name, Pid, Meta, Time, Reason}, [RequesterNode], State),
%% broadcast (include self() so receiver can set up monitor if needed)
syn_gen_scope:broadcast({'3.0', sync_register, Name, Pid, Meta, Time, Reason, self()}, [RequesterNode], State),
%% return
{reply, {ok, {CallbackMethod, PreviousMeta, Meta, Time, TableByName, TableByPid}}, State}.

Expand Down Expand Up @@ -690,7 +709,7 @@ resolve_conflict(Scope, Name, {Pid, Meta, Time}, {TablePid, TableMeta, TableTime
ResolveTime = erlang:system_time(),
add_to_local_table(Name, TablePid, TableMeta, ResolveTime, TableMRef, TableByName, TableByPid),
%% broadcast to all (including remote node to update the time)
syn_gen_scope:broadcast({'3.0', sync_register, Name, TablePid, TableMeta, ResolveTime, syn_conflict_resolution}, State);
syn_gen_scope:broadcast({'3.0', sync_register, Name, TablePid, TableMeta, ResolveTime, syn_conflict_resolution, self()}, State);

Invalid ->
error_logger:info_msg("SYN[~s|~s<~s>] Registry CONFLICT for name ~p: ~p vs ~p -> none chosen (got: ~p)",
Expand Down