> This concerns only smalltalk objects, right ? Other memory allocated
> by my plugin will not be touched by the GC ?

Yes.

> Still I wonder ... If the system is frozen as long as the plugin
> executes the GC has no chance to run. I can see how threads will be a
> problem, but don't the same concerns apply to any stateful code ?

Yes it would. However, most primitives/ffi calls require the state only for
life-time of the primitive call itself in which case this isn't a problem.
If you do need state to be persistent across primitive calls you will have
to allocate it on the C heap and pass a handle to it back to the Smalltalk
side.

Cheers,
  - Andreas