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

Thread-local define:

#ifndef F2PY_THREAD_LOCAL_DECL
#if defined(_MSC_VER)
#define F2PY_THREAD_LOCAL_DECL __declspec(thread)
#elif defined(NPY_OS_MINGW)
#define F2PY_THREAD_LOCAL_DECL __thread
#elif defined(__STDC_VERSION__) \
      && (__STDC_VERSION__ >= 201112L) \
      && !defined(__STDC_NO_THREADS__) \
      && (!defined(__GLIBC__) || __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 12)) \
      && !defined(NPY_OS_OPENBSD) && !defined(NPY_OS_HAIKU)
/* __STDC_NO_THREADS__ was first defined in a maintenance release of glibc 2.12,
   see https://lists.gnu.org/archive/html/commit-hurd/2012-07/msg00180.html,
   so `!defined(__STDC_NO_THREADS__)` may give false positive for the existence
   of `threads.h` when using an older release of glibc 2.12
   See gh-19437 for details on OpenBSD */
#include <threads.h>
#define F2PY_THREAD_LOCAL_DECL thread_local
#elif defined(__GNUC__) \
      && (__GNUC__ > 4 || (__GNUC__ == 4 && (__GNUC_MINOR__ >= 4)))
#define F2PY_THREAD_LOCAL_DECL __thread
#endif
#endif

F2PY_USE_PYTHON_TLS is an old CLI option that I don't think is in use anymore.

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.