Error thrown by GTween at random times?

moopf

Hi all,

I appear to be having a very random error thrown by what I think is something going on in GTween. The error is:

<pre> invalid key to 'next' stack traceback:

But there's no stack trace being returned. Has anybody come across this before? If so, any ideas what causes it?

Cheers,

Gareth

Chang

I've came across this before. It is very random and occurred like 1 out of 100 times. I am not sure what is causing this as well.

bowerandy

@moopf, I haven't seen this particular error but I quite often see Lua errors that aren't accompanied by a stack trace. This makes finding the issue (which invariably is a coding error on my part) very difficult. Perhaps @atilim could take a look to see if this lack of stack trace can be fixed.

best regards

alexzheng

I remember @atilim has fixed this bug long before.

http://www.giderosmobile.com/forum/discussion/comment/266#Comment_266

moopf

@alexheng - that thread says he fixed 'a bug'. Possibly another one that hasn't been?

john26

You may be able to get your own stack traceback using the debug.traceback function and maybe calling GTween with the pcall function. The trouble is, by the time you can call debug.traceback, the stack may have already unwound...

Atilim should ensure, whenever he uses lua_pcall, there is an appropriate error handler function on the Lua stack and the last arg of lua_pcall references this.

atilim

http://www.lua.org/manual/5.1/manual.html#pdf-next
The behavior of next is undefined if, during the traversal, you assign any value to a non-existent field in the table. You may however modify existing fields. In particular, you may clear existing fields.

Here is a minimal code to get this error:

local t = {a = 1} for k,v in pairs(t) do t.a = nil -- deletion is allowed while iterating t.b = 2 -- but insertion is not end

Let me look GTween's code and try to find where I violate this rule. Also let me try to find why I cannot see the stack traceback for this case.

As a side note, to get stack traceback, I'm using db_errorfb function http://www.lua.org/source/5.1/ldblib.c.html#db_errorfb with lua_pcall internally.

john26

I hadn't heard of db_errorfb, it is not mentioned in the Lua reference manual I think?

Another option might be to use luaL_traceback instead..?

atilim

@john26 it's a function found in Lua sources. I haven't directly used luaL_traceback because I've done some small changes to db_errorfb.

atilim

Also I've improved displaying the stack traceback.

bowerandy

@atilim, just to let you know that I have seen this error occur twice this evening.

best regards

atilim

@bowerandy - can you see where it occurs?

bowerandy

@atilim, sorry, I don't have the stack trace. I do remember that it was not a full trace, there was only one line in it.

Best regards