[blattimwind]

The GIL is mostly managed by CPython and the host application doesn't touch it directly. Host extension modules may use PyEval_SaveThread et al. just like regular extension modules to release the GIL during blocking operations when called by CPython. There is a separate API for fondling the GIL when you're in a host-created thread (not created by CPython) and want to call CPython. Those are orthogonal (called by CPython vs. calling CPython).