Re: LuaJIT FFI callbacks (was Re: Calling lua functions from C when using luajit ffi.)

[Duncan Cross <duncan.cross@...>]

On Tue, Nov 15, 2011 at 5:15 AM, James McKaskill <james@foobar.co.nz> wrote:
>
> On Nov 14, 2011, at 19:30 , Duncan Cross wrote:
>>
>> This is fantastic news! Thanks so much for your work, and thanks too
>> to the anonymous sponsor.
>>
>> One thing - I'm not certain this is related to the addition of
>> callbacks, but I was just experimenting with Win32 calls and found
>> that GetLastError() seems to return the wrong value (127,
>> ERROR_PROC_NOT_FOUND) the first time it's called. This is a minimal
>> test case:
>>
>>  local ffi = require("ffi")
>>
>>  ffi.cdef [[
>>  uint32_t GetLastError();
>>  void SetLastError(uint32_t code);
>>  ]]
>>
>>  ffi.C.SetLastError(0)
>>  print(ffi.C.GetLastError()) -- 127
>>  ffi.C.SetLastError(0)
>>  print(ffi.C.GetLastError()) -- 0
>>
>> (I'm explicitly setting the error here, but I discovered it because it
>> was hiding a parameter error while I was experimenting with trying to
>> call RegisterClassExA().)
>>
>> -Duncan
>>
>
> I would not suggest trying to get errors using Get/SetLastError as they will be invalidated by the vm. If you really want the error use ffi.errno().
>
> -- James
>
>

It was specifically addressed before that it should work, and is not
the same thing as errno:

http://lua-users.org/lists/lua-l/2011-05/msg00219.html

"I've fixed this in git HEAD. LuaJIT now preserves errno across hooks,
memory allocations, invocations of the JIT compiler and other internal
VM activity. Ditto for GetLastError() on Windows.

(...)

On Windows you need to declare and call GetLastError() yourself (note:
this does _not_ hold the same value as errno)."

-Duncan