Created
September 16, 2022 04:48
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Weird Lua garbage collector behavior.
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| #include <stdio.h> | |
| #include "lua.h" | |
| #include "lauxlib.h" | |
| #include "lualib.h" | |
| static int outergc(lua_State *L) { | |
| void * n = lua_touserdata(L, lua_upvalueindex(1)); | |
| void * o = lua_touserdata(L, -1); | |
| printf("Outer gc called on %p with upvalue = %p\n", o, n); | |
| return 0; | |
| } | |
| static int innergc(lua_State *L) { | |
| void * n = lua_touserdata(L, -1); | |
| printf("Inner gc called on %p\n", n); | |
| return 0; | |
| } | |
| int main() { | |
| lua_State *L = luaL_newstate(); | |
| luaL_openlibs(L); | |
| lua_checkstack(L, 10); | |
| lua_newtable(L); | |
| // 1 = {} | |
| lua_pushstring(L, "_proxy"); | |
| // 1 = {}, 2 = "_proxy" | |
| void * o = lua_newuserdata(L, 1); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy | |
| printf("Created outer object: %p\n", o); | |
| lua_newtable(L); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {} | |
| lua_pushstring(L, "__gc"); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc" | |
| void * n = lua_newuserdata(L, 1); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc", 6 = upvalue | |
| printf("Created inner object: %p\n", n); | |
| lua_newtable(L); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc", 6 = upvalue, 7 = {} | |
| lua_pushstring(L, "__gc"); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc", 6 = upvalue, 7 = {}, 8 = "__gc" | |
| lua_pushcfunction(L, innergc); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc", 6 = upvalue, 7 = {}, 8 = "__gc", 9 = innergc | |
| lua_settable(L, 7); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc", 6 = upvalue, 7 = {__gc = innergc} | |
| lua_setmetatable(L, -1); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc", 6 = upvalue_with_gc | |
| lua_pushcclosure(L, outergc, 1); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = {}, 5 = "__gc", 6 = outergc_with_upvalue_with_gc | |
| lua_settable(L, 4); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy, 4 = { __gc = outergc_with_upvalue_with_gc } | |
| lua_setmetatable(L, 3); | |
| // 1 = {}, 2 = "_proxy", 3 = proxy_with_gc | |
| lua_settable(L, 1); | |
| // 1 = { _proxy = proxy_with_gc } | |
| lua_pop(L, 1); | |
| // empty stack | |
| lua_gc(L, LUA_GCCOLLECT, 0); | |
| printf("Closing...\n"); | |
| lua_close(L); | |
| } |
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