Using thread pool to do a computation in parallel with many thousand tasks, I noticed, that tpool leaks memory. The script attached demonstrates the loss both in ActiveTcl 220.127.116.11 on Windows/64 and in tcl8.6 HEAD on Mac OSX. My real computation ran for several hours on 6 cores and the leaked memory summed up to several hundred MB. I could not locate the leakage any further, first I thought the culprit was the tpool::wait command with the list result, but replacing it with a simple "after" in the test case has no influence. Also, tpool::release can not free the leaked memory.