> Nice work! I also think heap_gc_deadlock_lockless.diff is good, except for Victor's reservation: is it deliberate that you reversed the following two statements in _free_pending_blocks(), compared to the code in free()?
>
> +            self._free(block)
> +            self._allocated_blocks.remove(block)
>

No, it's not deliberate (it shouldn't have any impact since they're
protected by the mutex though).
As for calling _free_pending_blocks() a second time, I'm not sure
that's necessary, I find the code simpler and cleaner that way.
I'll provide a new patch in a couple days (no access to my development
box right now).