No Python thread is ever fork safe because the Python interpreter itself can never be made fork safe. Nor should anyone try to make the interpreter itself safe. It is too complex and effectively impossible to guarantee.

There is no general solution to this, fork and threading is simply broken in POSIX and no amount of duct tape outside of the OS kernel can fix it. My only desire is that we attempt to do the right thing when possible with the locks we know about within the standard library.