Optimize ThreadPool slightly.
#1200
| Job | Run time |
|---|---|
| 12m 31s | |
| 26m 57s | |
| 14m 35s | |
| 26m 48s | |
| 17m 5s | |
| 3m 2s | |
| 37s | |
| 2m 56s | |
| 43s | |
| 1m 20s | |
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| 2m 39s | |
| 5m 31s | |
| 3m 17s | |
| 2m 36s | |
| 2m 48s | |
| 2m 1s | |
| 42s | |
| 1m 52s | |
| 3m 58s | |
| 1m 54s | |
| 2m 33s | |
| 1m 16s | |
| 40s | |
| 2m 42s | |
| 4s | |
| 2h 23m 51s |