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added 'check_pids' option to gproc:table/2
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@uwiger @RJ
uwiger authored and RJ committed Jul 9, 2012
1 parent 258cb24 commit 9b07765
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13 changes: 12 additions & 1 deletion doc/gproc.md
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Expand Up @@ -1158,9 +1158,20 @@ Equivalent to [`table(Context, [])`](#table-2).<a name="table-2"></a>
<br></br> <br></br>






QLC table generator for the gproc registry. QLC table generator for the gproc registry.
Context specifies which subset of the registry should be queried. Context specifies which subset of the registry should be queried.
See [`http://www.erlang.org/doc/man/qlc.html`](http://www.erlang.org/doc/man/qlc.html).<a name="unreg-1"></a> See [`http://www.erlang.org/doc/man/qlc.html`](http://www.erlang.org/doc/man/qlc.html).

NOTE: By default, the gproc table generator will not filter out entries
belonging to processes that have just died, but which have yet to be cleared
out of the registry. Use the option `check_pids` (or `{check_pids, true}`)
if you want to filter out dead entries already in the query. There will be
some overhead associated with doing so, and given that the process monitoring
is asynchronous, there can never be any guarantee that there are no dead
entries in the list by the time your program processes it.
<a name="unreg-1"></a>


###unreg/1## ###unreg/1##


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87 changes: 57 additions & 30 deletions src/gproc.erl
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Expand Up @@ -2295,21 +2295,37 @@ table(Context) ->
%% @doc QLC table generator for the gproc registry. %% @doc QLC table generator for the gproc registry.
%% Context specifies which subset of the registry should be queried. %% Context specifies which subset of the registry should be queried.
%% See [http://www.erlang.org/doc/man/qlc.html]. %% See [http://www.erlang.org/doc/man/qlc.html].
%%
%% NOTE: By default, the gproc table generator will not filter out entries
%% belonging to processes that have just died, but which have yet to be cleared
%% out of the registry. Use the option `check_pids' (or `{check_pids, true}')
%% if you want to filter out dead entries already in the query. There will be
%% some overhead associated with doing so, and given that the process monitoring
%% is asynchronous, there can never be any guarantee that there are no dead
%% entries in the list by the time your program processes it.
%%
%% @end %% @end
table(Context, Opts) -> table(Context, Opts) ->
Ctxt = {_, Type} = get_s_t(Context), Ctxt = {_, Type} = get_s_t(Context),
[Traverse, NObjs] = [proplists:get_value(K,Opts,Def) || [Traverse, NObjs] = [proplists:get_value(K,Opts,Def) ||
{K,Def} <- [{traverse,select}, {n_objects,100}]], {K,Def} <- [{traverse,select}, {n_objects,100}]],
CheckPids = proplists:get_bool(check_pids, Opts),
TF = case Traverse of TF = case Traverse of
first_next -> first_next ->
fun() -> qlc_next(Ctxt, first(Ctxt)) end; fun() -> qlc_next(Ctxt, first(Ctxt), CheckPids) end;
last_prev -> fun() -> qlc_prev(Ctxt, last(Ctxt)) end; last_prev -> fun() -> qlc_prev(Ctxt, last(Ctxt), CheckPids) end;
select -> select ->
fun(MS) -> qlc_select( fun(MS) -> qlc_select(
select(Ctxt, wrap_qlc_ms_prod(MS), NObjs)) end; CheckPids,
select(Ctxt, wrap_qlc_ms_prod(CheckPids, MS),
NObjs))
end;
{select,MS} -> {select,MS} ->
fun() -> qlc_select( fun() -> qlc_select(
select(Ctxt, wrap_qlc_ms_prod(MS), NObjs)) end; CheckPids,
select(Ctxt, wrap_qlc_ms_prod(CheckPids, MS),
NObjs))
end;
_ -> _ ->
erlang:error(badarg, [Ctxt,Opts]) erlang:error(badarg, [Ctxt,Opts])
end, end,
Expand All @@ -2324,39 +2340,46 @@ table(Context, Opts) ->
LookupFun = LookupFun =
case Traverse of case Traverse of
{select, _MS} -> undefined; {select, _MS} -> undefined;
_ -> fun(Pos, Ks) -> qlc_lookup(Ctxt, Pos, Ks) end _ -> fun(Pos, Ks) -> qlc_lookup(Ctxt, Pos, Ks, CheckPids) end
end, end,
qlc:table(TF, [{info_fun, InfoFun}, qlc:table(TF, [{info_fun, InfoFun},
{lookup_fun, LookupFun}] ++ [{K,V} || {K,V} <- Opts, {lookup_fun, LookupFun}] ++ [{K,V} || {K,V} <- Opts,
K =/= traverse, K =/= traverse,
K =/= n_objects]). K =/= n_objects]).

wrap_qlc_ms_prod(false, Pats) ->
wrap_qlc_ms_prod(Pats) -> Pats;
wrap_qlc_ms_prod(true, Pats) ->
[ wrap_qlc_ms_prod_(P) || P <- Pats ]. [ wrap_qlc_ms_prod_(P) || P <- Pats ].


wrap_qlc_ms_prod_({H, Gs, [P]}) -> wrap_qlc_ms_prod_({H, Gs, [P]}) ->
{H, Gs, [{{ {element, 2, '$_'}, P }}]}. {H, Gs, [{{ {element, 2, '$_'}, P }}]}.


qlc_lookup(_Scope, 1, Keys) -> qlc_lookup(_Scope, 1, Keys, Check) ->
lists:flatmap( lists:flatmap(
fun(Key) -> fun(Key) ->
remove_dead( remove_dead(
Check,
ets:select(?TAB, [{ {{Key,'_'},'_','_'}, [], ets:select(?TAB, [{ {{Key,'_'},'_','_'}, [],
[{{ {element,1,{element,1,'$_'}}, [{{ {element,1,{element,1,'$_'}},
{element,2,'$_'}, {element,2,'$_'},
{element,3,'$_'} }}] }])) {element,3,'$_'} }}] }]))
end, Keys); end, Keys);
qlc_lookup(Scope, 2, Pids) -> qlc_lookup(Scope, 2, Pids, Check) ->
lists:flatmap(fun(Pid) -> lists:flatmap(fun(Pid) ->
qlc_lookup_pid(Pid, Scope) qlc_lookup_pid(Pid, Scope, Check)
end, Pids). end, Pids).


remove_dead(Objs) -> remove_dead(false, Objs) ->
Objs;
remove_dead(true, Objs) ->
[ Reg || {_, Pid, _} = Reg <- Objs, [ Reg || {_, Pid, _} = Reg <- Objs,
not ?PID_IS_DEAD(Pid) ]. not ?PID_IS_DEAD(Pid) ].


qlc_lookup_pid(Pid, Scope) -> %% While it may seem obsessive not to do the sensible pid liveness check here
case ?PID_IS_DEAD(Pid) of %% every time, we make it optional for consistency; this way, we can devise
%% a test case that verifies the difference between having the option and not.
qlc_lookup_pid(Pid, Scope, Check) ->
case Check andalso ?PID_IS_DEAD(Pid) of
true -> true ->
[]; [];
false -> false ->
Expand All @@ -2378,49 +2401,53 @@ qlc_lookup_pid(Pid, Scope) ->
end. end.




qlc_next(_, '$end_of_table') -> []; qlc_next(_, '$end_of_table', _) -> [];
qlc_next(Scope, K) -> qlc_next(Scope, K, Check) ->
case ets:lookup(?TAB, K) of case ets:lookup(?TAB, K) of
[{{Key,_}, Pid, V}] -> [{{Key,_}, Pid, V}] ->
case ?PID_IS_DEAD(Pid) of case Check andalso ?PID_IS_DEAD(Pid) of
true -> true ->
qlc_next(Scope, next(Scope, K)); qlc_next(Scope, next(Scope, K), Check);
false -> false ->
[{Key,Pid,V}] ++ fun() -> [{Key,Pid,V}] ++ fun() ->
qlc_next(Scope, next(Scope, K)) qlc_next(Scope, next(Scope, K),
Check)
end end
end; end;
[] -> [] ->
qlc_next(Scope, next(Scope, K)) qlc_next(Scope, next(Scope, K), Check)
end. end.


qlc_prev(_, '$end_of_table') -> []; qlc_prev(_, '$end_of_table', _) -> [];
qlc_prev(Scope, K) -> qlc_prev(Scope, K, Check) ->
case ets:lookup(?TAB, K) of case ets:lookup(?TAB, K) of
[{{Key,_},Pid,V}] -> [{{Key,_},Pid,V}] ->
case ?PID_IS_DEAD(Pid) of case Check andalso ?PID_IS_DEAD(Pid) of
true -> true ->
qlc_prev(Scope, prev(Scope, K)); qlc_prev(Scope, prev(Scope, K), Check);
false -> false ->
[{Key,Pid,V}] ++ fun() -> [{Key,Pid,V}] ++ fun() ->
qlc_prev(Scope, prev(Scope, K)) qlc_prev(Scope, prev(Scope, K),
Check)
end end
end; end;
[] -> [] ->
qlc_prev(Scope, prev(Scope, K)) qlc_prev(Scope, prev(Scope, K), Check)
end. end.


qlc_select('$end_of_table') -> qlc_select(_, '$end_of_table') ->
[]; [];
qlc_select({Objects, Cont}) -> qlc_select(true, {Objects, Cont}) ->
case [O || {Pid,O} <- Objects, case [O || {Pid,O} <- Objects,
not ?PID_IS_DEAD(Pid)] of not ?PID_IS_DEAD(Pid)] of
[] -> [] ->
%% re-run search %% re-run search
qlc_select(ets:select(Cont)); qlc_select(true, ets:select(Cont));
Found -> Found ->
Found ++ fun() -> qlc_select(ets:select(Cont)) end Found ++ fun() -> qlc_select(true, ets:select(Cont)) end
end. end;
qlc_select(false, {Objects, Cont}) ->
Objects ++ fun() -> qlc_select(false, ets:select(Cont)) end.




is_unique(n) -> true; is_unique(n) -> true;
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35 changes: 26 additions & 9 deletions test/gproc_tests.erl
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Original file line number Original file line Diff line number Diff line change
Expand Up @@ -474,38 +474,55 @@ t_qlc_dead() ->
%% local names %% local names
Exp1 = [{{n,l,{n,1}},self(),x}], Exp1 = [{{n,l,{n,1}},self(),x}],
?assertEqual(Exp1, ?assertEqual(Exp1,
qlc:e(qlc:q([N || N <- gproc:table(names)]))), qlc:e(qlc:q([N || N <-
gproc:table(names, [check_pids])]))),
?assertEqual(Exp1, ?assertEqual(Exp1,
qlc:e(qlc:q([N || {{n,l,_},_,_} = N <- qlc:e(qlc:q([N || {{n,l,_},_,_} = N <-
gproc:table(names)]))), gproc:table(names, [check_pids])]))),
%% match local names on value %% match local names on value
Exp2 = [{{n,l,{n,1}},self(),x}], Exp2 = [{{n,l,{n,1}},self(),x}],
?assertEqual(Exp2, ?assertEqual(Exp2,
qlc:e(qlc:q([N || {{n,l,_},_,x} = N <- qlc:e(qlc:q([N || {{n,l,_},_,x} = N <-
gproc:table(names)]))), gproc:table(names, [check_pids])]))),
?assertEqual([], ?assertEqual([],
qlc:e(qlc:q([N || {{n,l,_},_,y} = N <- qlc:e(qlc:q([N || {{n,l,_},_,y} = N <-
gproc:table(names)]))), gproc:table(names, [check_pids])]))),
%% match all on value %% match all on value
Exp3 = [{{n,l,{n,1}},self(),x}, Exp3 = [{{n,l,{n,1}},self(),x},
{{p,l,{p,1}},self(),x}], {{p,l,{p,1}},self(),x}],
?assertEqual(Exp3, ?assertEqual(Exp3,
qlc:e(qlc:q([N || {_,_,x} = N <- gproc:table(all)]))), qlc:e(qlc:q([N || {_,_,x} = N <-
gproc:table(all, [check_pids])]))),
?assertEqual([], ?assertEqual([],
qlc:e(qlc:q([N || {_,_,y} = N <- gproc:table(all)]))), qlc:e(qlc:q([N || {_,_,y} = N <-
gproc:table(all, [check_pids])]))),
Exp3b = [{{n,l,{n,2}},P1,y},
{{p,l,{p,2}},P1,y}],
?assertEqual(Exp3b,
qlc:e(qlc:q([N || {_,_,y} = N <-
gproc:table(all)]))),


%% match all %% match all
Exp4 = [{{n,l,{n,1}},self(),x}, Exp4 = [{{n,l,{n,1}},self(),x},
{{p,l,{p,1}},self(),x}], {{p,l,{p,1}},self(),x}],
?assertEqual(Exp4, ?assertEqual(Exp4,
qlc:e(qlc:q([X || X <- gproc:table(all)]))), qlc:e(qlc:q([X || X <-
gproc:table(all, [check_pids])]))),
%% match on pid %% match on pid
?assertEqual(Exp4, ?assertEqual(Exp4,
qlc:e(qlc:q([{K,P,V} || {K,P,V} <- qlc:e(qlc:q([{K,P,V} || {K,P,V} <-
gproc:table(all), P =:= self()]))), gproc:table(all, [check_pids]),
P =:= self()]))),
?assertEqual([], ?assertEqual([],
qlc:e(qlc:q([{K,P,V} || {K,P,V} <- qlc:e(qlc:q([{K,P,V} || {K,P,V} <-
gproc:table(all), P =:= P1]))) gproc:table(all, [check_pids]),
P =:= P1]))),
Exp4b = [{{n,l,{n,2}},P1,y},
{{p,l,{p,2}},P1,y}],
?assertEqual(Exp4b,
qlc:e(qlc:q([{K,P,V} || {K,P,V} <-
gproc:table(all),
P =:= P1])))
after after
sys:resume(gproc) sys:resume(gproc)
end. end.
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