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@@ -31,7 +31,8 @@
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-export([leader_call/1,
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leader_cast/1,
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- sync/0]).
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+ sync/0,
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+ get_leader/0]).
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%%% internal exports
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-export([init/1,
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@@ -54,7 +55,8 @@
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-record(state, {
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always_broadcast = false,
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- is_leader}).
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+ is_leader,
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+ sync_requests = []}).
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start_link() ->
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@@ -127,18 +129,29 @@ update_counter(_, _) ->
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%% @doc Synchronize with the gproc leader
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%%
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%% This function can be used to ensure that data has been replicated from the
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-%% leader to the current node.
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+%% leader to the current node. It does so by asking the leader to ping all
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+%% live participating nodes. The call will return `true' when all these nodes
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+%% have either responded or died. In the special case where the leader dies
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+%% during an ongoing sync, the call will fail with a timeout exception.
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+%% (Actually, it should be a `leader_died' exception; more study needed to find out
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+%% why gen_leader times out in this situation, rather than reporting that the
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+%% leader died.)
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%% @end
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%%
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sync() ->
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leader_call(sync).
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+get_leader() ->
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+ gen_leader:call(?MODULE, get_leader).
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+
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%%% ==========================================================
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handle_cast(_Msg, S, _) ->
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{stop, unknown_cast, S}.
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+handle_call(get_leader, _, S, E) ->
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+ {reply, gen_leader:leader_node(E), S};
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handle_call(_, _, S, _) ->
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{reply, badarg, S}.
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@@ -181,21 +194,41 @@ surrendered(S, {globals, Globs}, _E) ->
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handle_DOWN(Node, S, _E) ->
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+ S1 = check_sync_requests(Node, S),
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Head = {{{'_',g,'_'},'_'},'$1','_'},
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Gs = [{'==', {node,'$1'},Node}],
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Globs = ets:select(?TAB, [{Head, Gs, [{{{element,1,{element,1,'$_'}},
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{element,2,'$_'}}}]}]),
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case process_globals(Globs) of
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[] ->
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- {ok, S};
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+ {ok, S1};
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Broadcast ->
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- {ok, Broadcast, S}
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+ {ok, Broadcast, S1}
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end.
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%% ets:select_delete(?TAB, [{Head, Gs, [true]}]),
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%% {ok, [{delete, Globs}], S}.
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-handle_leader_call(sync, _From, S, _E) ->
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- {reply, true, sync, S};
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+check_sync_requests(Node, #state{sync_requests = SReqs} = S) ->
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+ SReqs1 = lists:flatmap(
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+ fun({From, Ns}) ->
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+ case Ns -- [Node] of
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+ [] ->
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+ gen_leader:reply(From, {leader, reply, true}),
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+ [];
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+ Ns1 ->
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+ [{From, Ns1}]
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+ end
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+ end, SReqs),
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+ S#state{sync_requests = SReqs1}.
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+
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+handle_leader_call(sync, From, #state{sync_requests = SReqs} = S, E) ->
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+ case gen_leader:alive(E) -- [node()] of
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+ [] ->
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+ {reply, true, S};
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+ Alive ->
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+ gen_leader:broadcast({from_leader, {sync, From}}, Alive, E),
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+ {noreply, S#state{sync_requests = [{From, Alive}|SReqs]}}
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+ end;
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handle_leader_call({reg, {C,g,Name} = K, Value, Pid}, _From, S, _E) ->
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case gproc_lib:insert_reg(K, Value, Pid, g) of
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false ->
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@@ -318,6 +351,25 @@ handle_leader_call({await, Key, Pid}, {_,Ref} = From, S, _E) ->
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handle_leader_call(_, _, S, _E) ->
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{reply, badarg, S}.
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+handle_leader_cast({sync_reply, Node, Ref}, S, _E) ->
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+ #state{sync_requests = SReqs} = S,
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+ case lists:keyfind(Ref, 1, SReqs) of
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+ false ->
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+ %% This should never happen, except perhaps if the leader who
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+ %% received the sync request died, and the new leader gets the
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+ %% sync reply. In that case, we trust that the client has been notified
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+ %% anyway, and ignore the message.
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+ {ok, S};
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+ {_, Ns} ->
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+ case lists:delete(Node, Ns) of
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+ [] ->
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+ gen_leader:reply(Ref, {leader, reply, true}),
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+ {ok, S#state{sync_requests = lists:keydelete(Ref,1,SReqs)}};
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+ Ns1 ->
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+ SReqs1 = lists:keyreplace(Ref, 1, SReqs, {Ref, Ns1}),
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+ {ok, S#state{sync_requests = SReqs1}}
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+ end
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+ end;
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handle_leader_cast({add_globals, Missing}, S, _E) ->
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%% This is an audit message: a peer (non-leader) had info about granted
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%% global resources that we didn't know of when we became leader.
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@@ -366,7 +418,8 @@ terminate(_Reason, _S) ->
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-from_leader(sync, S, _E) ->
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+from_leader({sync, Ref}, S, _E) ->
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+ gen_leader:leader_cast(?MODULE, {sync_reply, node(), Ref}),
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{ok, S};
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from_leader(Ops, S, _E) ->
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lists:foreach(
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Ulf Wiger