Don't leak old code when loading a modules with an on_load function

Normally, calling code:delete/1 before re-loading the code for a
module is unnecessary but causes no problem.

But there will be be problems if the new code has an on_load function.
Code with an on_load function will always be loaded as old code
to allowed it to be easily purged if the on_load function would fail.
If the on_load function succeeds, the old and current code will be
swapped.

So in the scenario where code:delete/1 has been called explicitly,
there is old code but no current code. Loading code with an
on_load function will cause the reference to the old code to be
overwritten. That will at best cause a memory leak, and at worst
an emulator crash (especially if NIFs are involved).

To avoid that situation, we will put the code with the on_load
function in a special, third slot in Module.

ERL-240

1 files changed, 1 insertions, 1 deletions

diff --git a/erts/preloaded/src/erts_internal.erl b/erts/preloaded/src/erts_internal.erl
index 6229754c8c..6aae5ba38c 100644
--- a/erts/preloaded/src/erts_internal.erl
+++ b/erts/preloaded/src/erts_internal.erl
@@ -304,7 +304,7 @@ release_literal_area_switch() ->
 
 -spec purge_module(Module, Op) -> boolean() when
       Module :: module(),
-      Op :: 'prepare' | 'abort' | 'complete'.
+      Op :: 'prepare' | 'prepare_on_load' | 'abort' | 'complete'.
 purge_module(_Module, _Op) ->
     erlang:nif_error(undefined).