Generation fails if generator uses `clone`

[dp1]

When a generator is multithreaded, it gets the syscall filter that solutions get, and a call to clone is blocked ( here ). This probably shouldn't happen.

Reproduced with a generator that uses numpy, like this:

import numpy
[...]

For this specific case, the problem can be worked around by disabling threading in numpy with os.environ['OPENBLAS_NUM_THREADS'] = '1', but the solution is obviously not generic