1 files changed, 91 insertions, 0 deletions
diff --git a/deps/rabbit/src/rabbit_boot_steps.erl b/deps/rabbit/src/rabbit_boot_steps.erl
new file mode 100644
index 0000000000..f87448edb7
--- /dev/null
+++ b/deps/rabbit/src/rabbit_boot_steps.erl
@@ -0,0 +1,91 @@
+%% This Source Code Form is subject to the terms of the Mozilla Public
+%% License, v. 2.0. If a copy of the MPL was not distributed with this
+%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
+%%
+%% Copyright (c) 2007-2020 VMware, Inc. or its affiliates.  All rights reserved.
+%%
+
+-module(rabbit_boot_steps).
+
+-export([run_boot_steps/0, run_boot_steps/1, run_cleanup_steps/1]).
+-export([find_steps/0, find_steps/1]).
+
+run_boot_steps() ->
+    run_boot_steps(loaded_applications()).
+
+run_boot_steps(Apps) ->
+    [begin
+      rabbit_log:info("Running boot step ~s defined by app ~s", [Step, App]),
+      ok = run_step(Attrs, mfa)
+    end || {App, Step, Attrs} <- find_steps(Apps)],
+    ok.
+
+run_cleanup_steps(Apps) ->
+    [run_step(Attrs, cleanup) || {_, _, Attrs} <- find_steps(Apps)],
+    ok.
+
+loaded_applications() ->
+    [App || {App, _, _} <- application:loaded_applications()].
+
+find_steps() ->
+    find_steps(loaded_applications()).
+
+find_steps(Apps) ->
+    All = sort_boot_steps(rabbit_misc:all_module_attributes(rabbit_boot_step)),
+    [Step || {App, _, _} = Step <- All, lists:member(App, Apps)].
+
+run_step(Attributes, AttributeName) ->
+    [begin
+        rabbit_log:debug("Applying MFA: M = ~s, F = ~s, A = ~p",
+                        [M, F, A]),
+        case apply(M,F,A) of
+            ok              -> ok;
+            {error, Reason} -> exit({error, Reason})
+        end
+     end
+      || {Key, {M,F,A}} <- Attributes,
+          Key =:= AttributeName],
+    ok.
+
+vertices({AppName, _Module, Steps}) ->
+    [{StepName, {AppName, StepName, Atts}} || {StepName, Atts} <- Steps].
+
+edges({_AppName, _Module, Steps}) ->
+    EnsureList = fun (L) when is_list(L) -> L;
+                     (T)                 -> [T]
+                 end,
+    [case Key of
+         requires -> {StepName, OtherStep};
+         enables  -> {OtherStep, StepName}
+     end || {StepName, Atts} <- Steps,
+            {Key, OtherStepOrSteps} <- Atts,
+            OtherStep <- EnsureList(OtherStepOrSteps),
+            Key =:= requires orelse Key =:= enables].
+
+sort_boot_steps(UnsortedSteps) ->
+    case rabbit_misc:build_acyclic_graph(fun vertices/1, fun edges/1,
+                                         UnsortedSteps) of
+        {ok, G} ->
+            %% Use topological sort to find a consistent ordering (if
+            %% there is one, otherwise fail).
+            SortedSteps = lists:reverse(
+                            [begin
+                                 {StepName, Step} = digraph:vertex(G,
+                                                                   StepName),
+                                 Step
+                             end || StepName <- digraph_utils:topsort(G)]),
+            digraph:delete(G),
+            %% Check that all mentioned {M,F,A} triples are exported.
+            case [{StepName, {M,F,A}} ||
+                     {_App, StepName, Attributes} <- SortedSteps,
+                     {mfa, {M,F,A}}               <- Attributes,
+                     code:ensure_loaded(M) =/= {module, M} orelse
+                     not erlang:function_exported(M, F, length(A))] of
+                []         -> SortedSteps;
+                MissingFns -> exit({boot_functions_not_exported, MissingFns})
+            end;
+        {error, {vertex, duplicate, StepName}} ->
+            exit({duplicate_boot_step, StepName});
+        {error, {edge, Reason, From, To}} ->
+            exit({invalid_boot_step_dependency, From, To, Reason})
+    end.