This does not seem to play nice with image dumping

[digikar99]

For example, on SBCL, after (defpymodule "matplotlib.pyplot" nil :lisp-package "PLT), I'm unable sb-ext:save-lisp-and-die:

* (ql:quickload "py4cl2-cffi")
To load "py4cl2-cffi":
  Load 1 ASDF system:
    py4cl2-cffi
; Loading "py4cl2-cffi"

("py4cl2-cffi")
* (py4cl2-cffi:defpymodule "matplotlib.pyplot" nil :lisp-package "PLT")
Defining PLT for accessing python package plt..
T
* (py4cl2-cffi:pystop) ; close the py4cl2-threads
NIL
* (sb-ext:save-lisp-and-die "plt.core" :compression 22)
  failed AVER: (SB-THREAD::THREAD-P SB-IMPL::THREAD)
This is probably a bug in SBCL itself. (Alternatively, SBCL might have been
corrupted by bad user code, e.g. by an undefined Lisp operation like
(FMAKUNBOUND 'COMPILE), or by stray pointers from alien code or from unsafe
Lisp code; or there might be a bug in the OS or hardware that SBCL is running
on.) If it seems to be a bug in SBCL itself, the maintainers would like to know
about it. Bug reports are welcome on the SBCL mailing lists, which you can find
at <http://sbcl.sourceforge.net/>.
* 

This doesn't seem like an inherent issue with the CFFI based approach, but perhaps something to do with how defpymodule works. In particular, replacing the defpymodule with import-module does not cause this issue, and core image is generated successfully.