Ben Peart <Ben.Peart@xxxxxxxxxxxxx> writes:
> + * Fetch the tree from the ODB for each peer directory in the
> + * n commits.
> + *
> + * For 2- and 3-way traversals, we try to avoid hitting the
> + * ODB twice for the same OID. This should yield a nice speed
> + * up in checkouts and merges when the commits are similar.
> + *
> + * We don't bother doing the full O(n^2) search for larger n,
> + * because wider traversals don't happen that often and we
> + * avoid the search setup.
It is sensible to optimize for common cases while leaving out the
complexity that is only needed to support rare cases.
> + * When 2 peer OIDs are the same, we just copy the tree
> + * descriptor data. This implicitly borrows the buffer
> + * data from the earlier cell.
cell meaning...?
> + for (i = 0; i < n; i++, dirmask >>= 1) {
> + if (i > 0 && are_same_oid(&names[i], &names[i - 1]))
> + newinfo->t[i] = newinfo->t[i - 1];
> + else if (i > 1 && are_same_oid(&names[i], &names[i - 2]))
> + newinfo->t[i] = newinfo->t[i - 2];
> + else {
> + const struct object_id *oid = NULL;
> + if (dirmask & 1)
> + oid = names[i].oid;
> +
> + /*
> + * fill_tree_descriptor() will load the tree from the
> + * ODB. Accessing the ODB is not thread safe so
> + * serialize access using the odb_mutex.
> + */
> + pthread_mutex_lock(&o->odb_mutex);
> + newinfo->buf[newinfo->nr_buf++] =
> + fill_tree_descriptor(newinfo->t + i, oid);
> + pthread_mutex_unlock(&o->odb_mutex);
> + }
> + }
> +
> + /*
> + * We can't play games with the cache bottom as we are processing
> + * the tree objects in parallel.
> + * newinfo->bottom = switch_cache_bottom(&newinfo->info);
> + */
Would the resulting code match corresponding entries from two/three
trees correctly with a tree with entries "foo." (blob), "foo/" (has
subtree), and "foo0" (blob) at the same time, without adjusting the
bottom? I am worried because cache_bottom stuff is not about
optimization but is about correctness.
> + /* All I really need here is fetch_and_add() */
> + pthread_mutex_lock(&o->work_mutex);
> + o->remaining_work++;
> + pthread_mutex_unlock(&o->work_mutex);
> + mpmcq_push(&o->queue, &newinfo->entry);
Nice. I like the general idea.
