Trace

Still requires a few fixes, but the main part is done.
Ah, OK, I missed that.
Add thrs on top of my scheme. You just need a single line for that:

To allocate a thread:
if quarantine_size > N, pop from quarantine list
otherwise allocate from cache and set thrs[thr->id] = thr

Since tid<->thr association is persistent, you never need to reset nor change the association.

And, yes, adding this to kt_cache_t looks wrong.