f2py snippet for a LAPACK function with a callback

f2py_callback_gees_user_routines.c

/******************* See f2py2e/cb_rules.py: buildcallback *******************/

/********************* cb_cselect_in_gees__user__routines *********************/
typedef struct {
    PyObject *capi;
    PyTupleObject *args_capi;
    int nofargs;
    jmp_buf jmpbuf;
} cb_cselect_in_gees__user__routines_t;

#if defined(F2PY_THREAD_LOCAL_DECL) && !defined(F2PY_USE_PYTHON_TLS)

static F2PY_THREAD_LOCAL_DECL cb_cselect_in_gees__user__routines_t *_active_cb_cselect_in_gees__user__routines = NULL;

static cb_cselect_in_gees__user__routines_t *swap_active_cb_cselect_in_gees__user__routines(cb_cselect_in_gees__user__routines_t *ptr) {
    cb_cselect_in_gees__user__routines_t *prev = _active_cb_cselect_in_gees__user__routines;
    _active_cb_cselect_in_gees__user__routines = ptr;
    return prev;
}

static cb_cselect_in_gees__user__routines_t *get_active_cb_cselect_in_gees__user__routines(void) {
    return _active_cb_cselect_in_gees__user__routines;
}

#else

static cb_cselect_in_gees__user__routines_t *swap_active_cb_cselect_in_gees__user__routines(cb_cselect_in_gees__user__routines_t *ptr) {
    char *key = "__f2py_cb_cb_cselect_in_gees__user__routines";
    return (cb_cselect_in_gees__user__routines_t *)F2PySwapThreadLocalCallbackPtr(key, ptr);
}

static cb_cselect_in_gees__user__routines_t *get_active_cb_cselect_in_gees__user__routines(void) {
    char *key = "__f2py_cb_cb_cselect_in_gees__user__routines";
    return (cb_cselect_in_gees__user__routines_t *)F2PyGetThreadLocalCallbackPtr(key);
}

#endif

Also the error handling may need to be looked at more closely, since it uses a global

static PyObject *_flapack_error;

which is modified from within functions.

The static pyobjects are fine since they refer to global objects that are read-only after module initialization.

F2PySwapThreadLocalCallbackPtr uses the PyThreadState C API to implement thread-local state if it can't do it using the low-level thread local C declaration modifier.

The actual definition of F2PY_THREAD_LOCAL_DECL seems reasonable. We also check for _Thread_local in NumPy but I doubt it matters much for this use.