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example/sources/dynamic_object.cpp dangerous example? #1640

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Maddimax opened this issue Nov 4, 2024 · 4 comments · May be fixed by #1641
Closed

example/sources/dynamic_object.cpp dangerous example? #1640

Maddimax opened this issue Nov 4, 2024 · 4 comments · May be fixed by #1641

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@Maddimax
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Maddimax commented Nov 4, 2024

I've been using the example/sources/dynamic_object.cpp for my own custom container-like type. I'm now running into crashes in my "sol::meta_function::index" function when it tries to access the stored sol::objects after a garbage collector run a while later.
(I call lua functions in response to various user interactions).

With my limited understanding I explain the crashes as:

  • Lua calls my dynamic_set function with a usertype value
  • I store said object
  • The object in the Lua code is no longer "active" and gets marked by the garbage collector
  • Some time later the garbage collector frees the object
  • When it the calls "dynamic_get", and I return the object from my internal store, it creates a reference to something lua already released?

Do I misunderstand the way lua keeps track of objects? Can/Should the sol::object keep the lua value "alive"?
@Maddimax
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Maddimax commented Nov 4, 2024

I'm getting a crash here.

Callstack:

frame #0: 0x000000015a8189d0 libLua.dylib`luaD_reallocstack(L=0x000000016a6eda78, newsize=1, raiseerror=0) at ldo.c:216:25
frame #1: 0x000000015a818ed4 libLua.dylib`luaD_growstack(L=0x000000016a6eda78, n=1, raiseerror=0) at ldo.c:261:14
frame #2: 0x000000015a80597c libLua.dylib`lua_checkstack(L=0x000000016a6eda78, n=1) at lapi.c:120:11
frame #3: 0x000000015a80b3d0 libLua.dylib`luaL_checkstack(L=0x000000016a6eda78, space=1, msg="not enough Lua stack space to push this reference value") at lauxlib.c:381:7
frame #4: 0x0000000159f2ebe0 libLua.dylib`sol::stateless_reference::push(this=0x000000016a6ef5d8, L_=0x000000016a6eda78) const at sol.hpp:10418:4
frame #5: 0x0000000159f445a8 libLua.dylib`sol::stateless_reference::copy_ref(this=0x000000016a6ef5d8, L_=0x000000016a6eda78) const at sol.hpp:10296:4
frame #6: 0x0000000159f44554 libLua.dylib`sol::basic_reference<false>::copy_ref(this=0x000000016a6ef5d8, L_=0x000000016a6eda78) const at sol.hpp:10584:32
frame #7: 0x0000000159f44508 libLua.dylib`sol::basic_reference<false>::copy_ref(this=0x000000016a6ef5d8) const at sol.hpp:10580:11
frame #8: 0x0000000159f444b4 libLua.dylib`sol::basic_reference<false>::basic_reference(this=0x000000016fdf9240, o=0x000000016a6ef5d8) at sol.hpp:10669:78
frame #9: 0x0000000159fcd8fc libLua.dylib`sol::basic_object_base<sol::basic_reference<false>>::basic_object_base(this=0x000000016fdf9240, (null)=0x000000016a6ef5d8) at sol.hpp:17052:3
frame #10: 0x0000000159fcd8c8 libLua.dylib`sol::basic_object<sol::basic_reference<false>>::basic_object(this=0x000000016fdf9240, (null)=0x000000016a6ef5d8) at sol.hpp:17119:3
frame #11: 0x000000015a327004 libLua.dylib`sol::basic_object<sol::basic_reference<false>>::basic_object(this=0x000000016fdf9240, (null)=0x000000016a6ef5d8) at sol.hpp:17119:45
frame #12: 0x000000015a2fcd24 libLua.dylib`Lua::Internal::LuaAspectContainer::dynamic_get(this=0x000000016a6ee030, key="generalSettings") at settings.cpp:31:16

image

The L looks quite "dead" to me.

@Maddimax
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Maddimax commented Nov 4, 2024

It turns out the issue is that new_index is called from a coroutine. Once that coroutine is done it seems that I cannot use sol::object's anymore that originate from it. Since we store the object ...

Is that expected?

@Maddimax
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Maddimax commented Nov 4, 2024 •
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I changed my dynamic_set to:

    void dynamic_set(const std::string &key, sol::stack_object value)
    {
        // m_lua is the LuaState of the main thread
        if (value.lua_state() != m_lua.lua_state()) {
            // This pushes the reference onto the other Lua State and returns a stack reference
            // to it.
            sol::stack_reference newRef = sol::stack_reference(m_lua, value);
            dynamic_set(key, newRef);
            return;
        }
        ...

that seems to solve the issue.

@Maddimax Maddimax mentioned this issue Nov 5, 2024
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@Maddimax
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Maddimax commented Nov 5, 2024

Turns out there is "main_object" etc. that does what I manually did.

@Maddimax Maddimax closed this as completed Nov 5, 2024
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Use main_object in dynamic_object example Maddimax/sol2
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