From 86fa667f9731c790d6575f31efa156c02cb7984b Mon Sep 17 00:00:00 2001
From: Richard Carlsson <richardc@klarna.com>
Date: Thu, 19 May 2016 20:29:45 +0200
Subject: Add code:module_status/1 and modified_modules/0

These functions use the MD5 beam/native checksum to determine whether the
code for a module has changed on disk and is a candidate for loading.
---
 lib/kernel/src/code.erl | 98 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 97 insertions(+), 1 deletion(-)

(limited to 'lib/kernel/src')

diff --git a/lib/kernel/src/code.erl b/lib/kernel/src/code.erl
index 0ad0676f98..5a7ca493cc 100644
--- a/lib/kernel/src/code.erl
+++ b/lib/kernel/src/code.erl
@@ -70,7 +70,9 @@
 	 where_is_file/2,
 	 set_primary_archive/4,
 	 clash/0,
-     get_mode/0]).
+         module_status/1,
+         modified_modules/0,
+         get_mode/0]).
 
 -deprecated({rehash,0,next_major_release}).
 
@@ -895,3 +897,97 @@ load_all_native_1([{Mod,BeamFilename}|T], ChunkTag) ->
     load_all_native_1(T, ChunkTag);
 load_all_native_1([], _) ->
     ok.
+
+%% Returns the status of the module in relation to object file on disk.
+-spec module_status(Module :: module()) -> not_loaded | loaded | modified | removed.
+module_status(Module) ->
+    module_status(Module, code:get_path()).
+
+%% Note that we don't want to go via which/1, since it doesn't look at the
+%% disk contents at all if the module is already loaded.
+module_status(Module, PathFiles) ->
+    case code:is_loaded(Module) of
+        false -> not_loaded;
+        {file, preloaded} -> loaded;
+        {file, cover_compiled} ->
+            %% cover compilation loads directly to memory and does not
+            %% create a beam file, so report 'modified' if a file exists
+            case which(Module, PathFiles) of
+                non_existing -> removed;
+                _File -> modified
+            end;
+        {file, []} -> loaded;  % no beam file - generated code
+        {file, OldFile} when is_list(OldFile) ->
+            %% we don't care whether or not the file is in the same location
+            %% as when last loaded, as long as it can be found in the path
+            case which(Module, PathFiles) of
+                non_existing -> removed;
+                Path ->
+                    case module_changed_on_disk(Module, Path) of
+                        true -> modified;
+                        false -> loaded
+                    end
+            end
+    end.
+
+%% Detects actual code changes only, e.g. to decide whether a module should
+%% be reloaded; does not care about file timestamps or compilation time
+module_changed_on_disk(Module, Path) ->
+    MD5 = erlang:get_module_info(Module, md5),
+    case erlang:system_info(hipe_architecture) of
+        undefined ->
+            %% straightforward, since native is not supported
+            MD5 =/= beam_file_md5(Path);
+        Architecture ->
+            case code:is_module_native(Module) of
+                true ->
+                    %% MD5 is for native code, so we check only the native
+                    %% code on disk, ignoring the beam code
+                    MD5 =/= beam_file_native_md5(Path, Architecture);
+                _ ->
+                    %% MD5 is for beam code, so check only the beam code on
+                    %% disk, even if the file contains native code as well
+                    MD5 =/= beam_file_md5(Path)
+            end
+    end.
+
+beam_file_md5(Path) ->
+    case beam_lib:md5(Path) of
+        {ok,{_Mod,MD5}} -> MD5;
+        _ -> undefined
+    end.
+
+beam_file_native_md5(Path, Architecture) ->
+    try
+        get_beam_chunk(Path, hipe_unified_loader:chunk_name(Architecture))
+    of
+        NativeCode when is_binary(NativeCode) ->
+            erlang:md5(NativeCode)
+    catch
+        _:_ -> undefined
+    end.
+
+get_beam_chunk(Path, Chunk) ->
+    {ok, {_, [{_, Bin}]}} = beam_lib:chunks(Path, [Chunk]),
+    Bin.
+
+%% Returns a list of all modules modified on disk.
+-spec modified_modules() -> [module()].
+modified_modules() ->
+    PathFiles = path_files(),
+    [M || {M, _} <- code:all_loaded(),
+          module_status(M, PathFiles) =:= modified].
+
+%% prefetch the directory contents of code path directories
+path_files() ->
+    path_files(code:get_path()).
+
+path_files([]) ->
+    [];
+path_files([Path|Tail]) ->
+    case erl_prim_loader:list_dir(Path) of
+        {ok, Files} ->
+            [{Path,Files} | path_files(Tail)];
+        _Error ->
+            path_files(Tail)
+    end.
-- 
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