gctest.c

#include <stdio.h>
#include <assert.h>

#include "lua.h"
#include "lauxlib.h"

static int num_allocated = 0;

static int l_newthing(lua_State *l) {
    lua_newuserdata(l, sizeof(void*));

    lua_getglobal(l, "metatable");
    lua_setmetatable(l, -2);

    num_allocated++;
    printf("  alloc: %d objects\n", num_allocated);

    return 1;
}

static int l_gc(lua_State *l) {
    num_allocated--;
    printf("dealloc: %d objects\n", num_allocated);

    return 0;
}

int main(int argc, char **argv) {
    lua_State *l = luaL_newstate();

    lua_newtable(l);
    lua_pushstring(l, "__gc");
    lua_pushcfunction(l, l_gc);
    lua_rawset(l, -3);
    lua_setglobal(l, "metatable");

    lua_pushcfunction(l, l_newthing);
    lua_setglobal(l, "newthing");

    assert(!luaL_loadstring(l, "for i = 1,10000 do newthing() end"));
    lua_call(l, 0, 1);

    printf("done! inspect the process, then press enter to finish\n");
    getc(stdin);

    lua_close(l);

    return 0;
}