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-rw-r--r--erts/emulator/test/map_SUITE.erl71
1 files changed, 71 insertions, 0 deletions
diff --git a/erts/emulator/test/map_SUITE.erl b/erts/emulator/test/map_SUITE.erl
index 91a5706320..1da08beb8b 100644
--- a/erts/emulator/test/map_SUITE.erl
+++ b/erts/emulator/test/map_SUITE.erl
@@ -62,6 +62,7 @@
t_maps_without/1,
%% misc
+ t_hashmap_balance/1,
t_pdict/1,
t_ets/1,
t_dets/1,
@@ -111,6 +112,7 @@ all() -> [
%% Other functions
+ t_hashmap_balance,
t_pdict,
t_ets,
t_tracing
@@ -1421,6 +1423,75 @@ t_maps_without(_Config) ->
%% MISC
+
+%% Verify that the the number of nodes in hashmaps
+%% of different types and sizes does not deviate too
+%% much from the theoretical model.
+t_hashmap_balance(_Config) ->
+ io:format("Integer keys\n", []),
+ hashmap_balance(fun(I) -> I end),
+ io:format("Float keys\n", []),
+ hashmap_balance(fun(I) -> float(I) end),
+ io:format("String keys\n", []),
+ hashmap_balance(fun(I) -> integer_to_list(I) end),
+ io:format("Binary (big) keys\n", []),
+ hashmap_balance(fun(I) -> <<I:16/big>> end),
+ io:format("Binary (little) keys\n", []),
+ hashmap_balance(fun(I) -> <<I:16/little>> end),
+ io:format("Atom keys\n", []),
+ erts_debug:set_internal_state(available_internal_state, true),
+ hashmap_balance(fun(I) -> erts_debug:get_internal_state({atom,I}) end),
+ erts_debug:set_internal_state(available_internal_state, false),
+
+ ok.
+
+hashmap_balance(KeyFun) ->
+ F = fun(I, {M0,Max0}) ->
+ Key = KeyFun(I),
+ M1 = M0#{Key => Key},
+ Max1 = case erts_internal:map_type(M1) of
+ hashmap ->
+ Nodes = hashmap_nodes(M1),
+ Avg = maps:size(M1) * 0.4,
+ StdDev = math:sqrt(maps:size(M1)) / 3,
+ SD_diff = abs(Nodes - Avg) / StdDev,
+ %%io:format("~p keys: ~p nodes avg=~p SD_diff=~p\n",
+ %% [maps:size(M1), Nodes, Avg, SD_diff]),
+ {MaxDiff0, _} = Max0,
+ case {Nodes > Avg, SD_diff > MaxDiff0} of
+ {true, true} -> {SD_diff, M1};
+ _ -> Max0
+ end;
+
+ flatmap -> Max0
+ end,
+ {M1, Max1}
+ end,
+
+ {_,{MaxDiff,MaxMap}} = lists:foldl(F,
+ {#{}, {0, 0}},
+ lists:seq(1,10000)),
+ io:format("Max std dev diff ~p for map of size ~p (nodes=~p, flatsize=~p)\n",
+ [MaxDiff, maps:size(MaxMap), hashmap_nodes(MaxMap), erts_debug:flat_size(MaxMap)]),
+
+ true = (MaxDiff < 6), % The probability of this line failing is about 0.000000001
+ % for a uniform hash. I've set the probability this "high" for now
+ % to detect flaws in our make_internal_hash.
+ % Hard limit is 15 (see hashmap_over_estimated_heap_size).
+ ok.
+
+hashmap_nodes(M) ->
+ Info = erts_debug:map_info(M),
+ lists:foldl(fun(Tpl,Acc) ->
+ case element(1,Tpl) of
+ bitmaps -> Acc + element(2,Tpl);
+ arrays -> Acc + element(2,Tpl);
+ _ -> Acc
+ end
+ end,
+ 0,
+ Info).
+
t_pdict(_Config) ->
put(#{ a => b, b => a},#{ c => d}),