From bf0b86ea8e71d05331ef36c472f4dee646b22c38 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Thu, 12 Apr 2018 11:54:47 +0200
Subject: erts: Add erts_debug:lc_graph/0

Run debug VM or config with --enable-lock-checking.

Exercise VM and then run

erts_debug:lc_graph().

to create a file "lc_graph.<pid>" in current working directory.
---
 lib/kernel/src/erts_debug.erl | 90 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 89 insertions(+), 1 deletion(-)

(limited to 'lib')

diff --git a/lib/kernel/src/erts_debug.erl b/lib/kernel/src/erts_debug.erl
index 6f248626ca..1270de4144 100644
--- a/lib/kernel/src/erts_debug.erl
+++ b/lib/kernel/src/erts_debug.erl
@@ -35,7 +35,8 @@
          flat_size/1, get_internal_state/1, instructions/0,
          map_info/1, same/2, set_internal_state/2,
          size_shared/1, copy_shared/1, dirty_cpu/2, dirty_io/2, dirty/3,
-         lcnt_control/1, lcnt_control/2, lcnt_collect/0, lcnt_clear/0]).
+         lcnt_control/1, lcnt_control/2, lcnt_collect/0, lcnt_clear/0,
+         lc_graph/0, lc_graph_to_dot/2, lc_graph_merge/2]).
 
 -spec breakpoint(MFA, Flag) -> non_neg_integer() when
       MFA :: {Module :: module(),
@@ -407,3 +408,90 @@ cont_dis(_, {_,_,_}, _) -> ok.
 
 map_info(_) ->
     erlang:nif_error(undef).
+
+%% Create file "lc_graph.<pid>" with all actual lock dependencies
+%% recorded so far by the VM.
+%% Needs debug VM or --enable-lock-checking config, returns 'notsup' otherwise.
+lc_graph() ->
+    erts_debug:set_internal_state(available_internal_state, true),
+    erts_debug:get_internal_state(lc_graph).
+
+%% Convert "lc_graph.<pid>" file to https://www.graphviz.org dot format.
+lc_graph_to_dot(OutFile, InFile) ->
+    {ok, [LL0]} = file:consult(InFile),
+
+    [{"NO LOCK",0} | LL] = LL0,
+    Map = maps:from_list([{Id, Name} || {Name, Id, _, _} <- LL]),
+
+    case file:open(OutFile, [exclusive]) of
+        {ok, Out} ->
+            ok = file:write(Out, "digraph G {\n"),
+
+            [dot_print_lock(Out, Lck, Map) || Lck <- LL],
+
+            ok = file:write(Out, "}\n"),
+            ok = file:close(Out);
+
+        {error,eexist} ->
+            {"File already exists", OutFile}
+    end.
+
+dot_print_lock(Out, {_Name, Id, Lst, _}, Map) ->
+    [dot_print_edge(Out, From, Id, Map) || From <- Lst],
+    ok.
+
+dot_print_edge(_, 0, _, _) ->
+    ignore; % "NO LOCK"
+dot_print_edge(Out, From, To, Map) ->
+    io:format(Out, "~p -> ~p;\n", [maps:get(From,Map), maps:get(To,Map)]).
+
+
+%% Merge several "lc_graph" files into one file.
+lc_graph_merge(OutFile, InFiles) ->
+    LLs = lists:map(fun(InFile) ->
+                            {ok, [LL]} = file:consult(InFile),
+                            LL
+                    end,
+                    InFiles),
+
+    Res = lists:foldl(fun(A, B) -> lcg_merge(A, B) end,
+                      hd(LLs),
+                      tl(LLs)),
+    case file:open(OutFile, [exclusive]) of
+        {ok, Out} ->
+            try
+                lcg_print(Out, Res)
+            after
+                file:close(Out)
+            end,
+            ok;
+        {error, eexist} ->
+            {"File already exists", OutFile}
+    end.
+
+lcg_merge(A, B) ->
+    lists:zipwith(fun(LA, LB) -> lcg_merge_locks(LA, LB) end,
+                  A, B).
+
+lcg_merge_locks(L, L) ->
+    L;
+lcg_merge_locks({Name, Id, DA, IA}, {Name, Id, DB, IB}) ->
+    Direct = lists:umerge(DA, DB),
+    Indirect = lists:umerge(IA, IB),
+    {Name, Id, Direct, Indirect -- Direct}.
+
+
+lcg_print(Out, LL) ->
+    io:format(Out, "[", []),
+    lcg_print_locks(Out, LL),
+    io:format(Out, "].\n", []),
+    ok.
+
+lcg_print_locks(Out, [{_,_}=NoLock | Rest]) ->
+    io:format(Out, "~p,\n", [NoLock]),
+    lcg_print_locks(Out, Rest);
+lcg_print_locks(Out, [LastLock]) ->
+    io:format(Out, "~w", [LastLock]);
+lcg_print_locks(Out, [Lock | Rest]) ->
+    io:format(Out, "~w,\n", [Lock]),
+    lcg_print_locks(Out, Rest).
-- 
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