Does anyone know where it is defined in the source?

I'm having issues in the Shuffler (which have been there for ages already) where a C-struct is being freed, but then after that, a callback is being called from pike which still references the (now freed) C-struct.

The freeing of the C-struct needs to be delayed until all references to the callback function are gone (which probably implies that I need to turn the struct over to the garbage collector, which implies that it needs to be an svalue, I presume). If anyone has better ideas for this, I'm all ears.