Comment 6 for bug 417053

Thanks for investigating the problem.

Leaked threads are known about, selftest will even report about them (when it can finish that is).
The crash with "can't start new thread" is pretty new though but is also blocking the test suite to run under cygwin.

As you discovered, some threads can be garbage collected, some others can't.
Most of them though are caused by test server threads and we can't easily terminate them due to our
transport objects design. This is known and there may even be a bug filed about adding a close() method for them.

In the mean time, try running less tests with the --starting-with option of by specifying some regexp.
Another work around may be to try https://code.launchpad.net/~vila/bzr/selftest-fixes/ that changes the way --parallel=fork work and spawn more subprocesses with less tests each.

You can even tweak the way the slices are calculated until you reach a point where selftest doesn't bomb anymore.