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Set the metatable of __gc'ed userdata to something more informative

This commit is contained in:
kyren 2018-02-05 14:39:01 -05:00
parent 6382baa991
commit fe35742026
2 changed files with 67 additions and 8 deletions
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2
src/userdata.rs
View File

@ -548,7 +548,7 @@ mod tests {
}
#[test]
fn test_expired_userdata() {
fn test_gc_userdata() {
struct MyUserdata {
id: u8,
}

71
src/util.rs
View File

@ -250,13 +250,12 @@ pub unsafe fn get_userdata<T>(state: *mut ffi::lua_State, index: c_int) -> *mut
pub unsafe extern "C" fn userdata_destructor<T>(state: *mut ffi::lua_State) -> c_int {
callback_error(state, || {
// We clear the metatable of userdata on __gc so that it will not be double dropped, and
// also so that it cannot be used or identified as any particular userdata type after the
// first call to __gc.
gc_guard(state, || {
ffi::lua_newtable(state);
// We set the metatable of userdata on __gc to a special table with no __gc method and with
// metamethods that trigger an error on access. We do this so that it will not be double
// dropped, and also so that it cannot be used or identified as any particular userdata type
// after the first call to __gc.
get_gc_userdata_metatable(state);
ffi::lua_setmetatable(state, -2);
});
let ud = &mut *(ffi::lua_touserdata(state, 1) as *mut T);
mem::replace(ud, mem::uninitialized());
Ok(0)
@ -588,3 +587,63 @@ unsafe fn get_panic_metatable(state: *mut ffi::lua_State) -> c_int {
ffi::LUA_TTABLE
}
unsafe fn get_gc_userdata_metatable(state: *mut ffi::lua_State) -> c_int {
static GC_USERDATA_METATABLE: u8 = 0;
unsafe extern "C" fn gc_error(state: *mut ffi::lua_State) -> c_int {
ffi::lua_pushstring(state, cstr!("userdata has been garbage collected"));
ffi::lua_error(state)
}
ffi::lua_pushlightuserdata(state, &GC_USERDATA_METATABLE as *const u8 as *mut c_void);
let t = ffi::lua_gettable(state, ffi::LUA_REGISTRYINDEX);
if t != ffi::LUA_TTABLE {
ffi::lua_pop(state, 1);
ffi::luaL_checkstack(state, 8, ptr::null());
gc_guard(state, || {
ffi::lua_newtable(state);
ffi::lua_pushlightuserdata(state, &GC_USERDATA_METATABLE as *const u8 as *mut c_void);
ffi::lua_pushvalue(state, -2);
for &method in &[
cstr!("__add"),
cstr!("__sub"),
cstr!("__mul"),
cstr!("__div"),
cstr!("__mod"),
cstr!("__pow"),
cstr!("__unm"),
cstr!("__idiv"),
cstr!("__band"),
cstr!("__bor"),
cstr!("__bxor"),
cstr!("__bnot"),
cstr!("__shl"),
cstr!("__shr"),
cstr!("__concat"),
cstr!("__len"),
cstr!("__eq"),
cstr!("__lt"),
cstr!("__le"),
cstr!("__index"),
cstr!("__newindex"),
cstr!("__call"),
cstr!("__tostring"),
cstr!("__pairs"),
cstr!("__ipairs"),
] {
ffi::lua_pushstring(state, method);
ffi::lua_pushcfunction(state, gc_error);
ffi::lua_rawset(state, -3);
}
ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
});
}
ffi::LUA_TTABLE
}