erts: Implement batching maps:iterator

This iterator implementation fetches multiple elements to
iterate over in one call to erts_internal:maps_next instead
of one at a time. This means that the memory usage will go
up for the iterator as we are buffering elements, but the
usage is still bounded.

In this implementation the max memory usage is 1000 words.

Using this approach makes the iterator as fast as using
maps:to_list, so maps:iterator/2 has been removed.

1 files changed, 9 insertions, 30 deletions

diff --git a/lib/stdlib/test/maps_SUITE.erl b/lib/stdlib/test/maps_SUITE.erl
index 0021dd0657..a75751b31d 100644
--- a/lib/stdlib/test/maps_SUITE.erl
+++ b/lib/stdlib/test/maps_SUITE.erl
@@ -30,7 +30,7 @@
 -export([t_update_with_3/1, t_update_with_4/1,
          t_get_3/1, t_filter_2/1,
          t_fold_3/1,t_map_2/1,t_size_1/1,
-         t_iterator_1/1, t_iterator_2/1,
+         t_iterator_1/1,
          t_with_2/1,t_without_2/1]).
 
 %%-define(badmap(V,F,Args), {'EXIT', {{badmap,V}, [{maps,F,Args,_}|_]}}).
@@ -48,7 +48,7 @@ all() ->
     [t_update_with_3,t_update_with_4,
      t_get_3,t_filter_2,
      t_fold_3,t_map_2,t_size_1,
-     t_iterator_1, t_iterator_2,
+     t_iterator_1,
      t_with_2,t_without_2].
 
 t_update_with_3(Config) when is_list(Config) ->
@@ -179,40 +179,19 @@ t_iterator_1(Config) when is_list(Config) ->
 
     %% Large map test
 
-    Vs = lists:seq(1,200),
-    M2 = maps:from_list([{{k,I},I}||I<-Vs]),
+    Vs2 = lists:seq(1,200),
+    M2 = maps:from_list([{{k,I},I}||I<-Vs2]),
     KVList2 = lists:sort(iter_kv(maps:iterator(M2))),
     KVList2 = lists:sort(maps:to_list(M2)),
-    ok.
 
-t_iterator_2(Config) when is_list(Config) ->
-
-    Vs = lists:seq(1,200),
-    Maps = [#{ a => 1, b => 2 }, maps:from_list([{{k,I},I}||I<-Vs])],
-    Optimize = [speed, memory],
-    Ordered = [true, false],
-
-    [test_iterator(Map, Opt, Ord) || Map <- Maps,
-                                     Opt <- Optimize,
-                                     Ord <- Ordered],
+    %% Larger map test
 
+    Vs3 = lists:seq(1,10000),
+    M3 = maps:from_list([{{k,I},I}||I<-Vs3]),
+    KVList3 = lists:sort(iter_kv(maps:iterator(M3))),
+    KVList3 = lists:sort(maps:to_list(M3)),
     ok.
 
-test_iterator(Map, Opt, Ord) ->
-    Opts = #{ optimize => Opt, ordered => Ord },
-    test_iterator_1(maps:iterator(Map, Opts), Map, Opts).
-
-test_iterator_1(Iter, OrigMap, Opts) ->
-    erlang:display(Opts),
-    KVs = iter_kv(Iter),
-    case Opts of
-        #{ ordered := true } ->
-            KVs = lists:sort(maps:to_list(OrigMap));
-        #{ ordered := false } ->
-            OrderedKVs = lists:sort(KVs),
-            OrderedKVs = lists:sort(maps:to_list(OrigMap))
-    end.
-
 iter_kv(I) ->
     case maps:next(I) of
         none ->