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, 0 deletions

diff --git a/erts/emulator/beam/module.h b/erts/emulator/beam/module.h
index 5a60bc90d9..1c1afc8461 100644
--- a/erts/emulator/beam/module.h
+++ b/erts/emulator/beam/module.h
@@ -39,6 +39,7 @@ typedef struct erl_module {
 
     struct erl_module_instance curr;
     struct erl_module_instance old; /* protected by "old_code" rwlock */
+    struct erl_module_instance* on_load;
 } Module; 
 
 Module* erts_get_module(Eterm mod, ErtsCodeIndex code_ix);