Compared to the previous commit:

| Benchmark          | 36_threadpool_opt_PR | 36_threadpool_opt_cond10    |
+--------------------+----------------------+-----------------------------+
| imap_unordered_seq | 1.06 ms              | 1.02 ms: 1.04x faster (-4%) |
| imap_unordered_par | 965 us               | 928 us: 1.04x faster (-4%)  |
| imap_seq           | 1.08 ms              | 1.03 ms: 1.04x faster (-4%) |
| map_seq            | 785 us               | 870 us: 1.11x slower (+11%) |
| map_par            | 656 us               | 675 us: 1.03x slower (+3%)  |
| apply              | 1.14 ms              | 1.12 ms: 1.02x faster (-2%) |