Rust Python FFI with Python function defintion called by Rust (broken)

readme.md

Note: Sorry, this code is incredibly messy. I'm trying to make this work, but it does not yet at all.

Problem

I get a segmentation fault when calling the function passed by reference. Calling the main

Issue

xxx@linux-fkyc:~/Workspace/nyxbin/src> python3 example_build.py 
generating ./_my_example.c
running build_ext
building '_my_example' extension
/usr/bin/gcc -Wno-unused-result -DNDEBUG -fmessage-length=0 -grecord-gcc-switches -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -DOPENSSL_LOAD_CONF -fPIC -I/usr/include/python3.4m -c _my_example.c -o ./_my_example.o
gcc -pthread -shared ./_my_example.o -L/usr/lib64 -lpython3.4m -o ./_my_example.cpython-34m.so

xxx@linux-fkyc:~/Workspace/nyxbin/src> python3 loader.py 
<cffi.api._make_ffi_library.<locals>.FFILibrary object at 0x7f9d4ba509b0> ['dyndisp_negate', 'dyndisp_t2']
t2
t2: 2
Segmentation fault (core dumped)

Cargo.toml

[package]
name = "nyxbin"
version = "0.1.0"
authors = ["XX <YY@ZZ.com>"]

[dependencies]
nalgebra = "0.14.0"

[lib]
name = "nyxbin"
crate-type = ["dylib"]

example.py

from _my_example import ffi
from cffi import FFI

ffibuilder = FFI()
lib = ffibuilder.dlopen("../libnyxbin.so")

# @ffi.callback("int(int, int *)")
# def python_callback(how_many, values):
#     print ffi.unpack(values, how_many)
#     return 0
#lib.python_callback = python_callback


@ffi.def_extern()
def my_bool_func_py(val):
    print("python says {}".format(val))
    return val


@ffi.def_extern()
def my_int_func_py():
    print("in my_int_func_py")
    #print("in my_int_func_py: {}".format(val))
    return

# print ("rust: {}".format(lib.dyndisp_negate(True, my_bool_func_py)))

example_build.py

# file "example_build.py"

import cffi

ffibuilder = cffi.FFI()
lib = ffibuilder.dlopen("../libnyxbin.so")

ffibuilder.cdef("""
    extern "Python" bool my_bool_func_py(bool);
    extern "Python" void my_int_func_py();
""")

ffibuilder.set_source("_my_example", r"""
    #include <stdbool.h>
    bool dyndisp_negate(bool pyval, bool (*fun)(bool));
    int dyndisp_t2(int pyval, void (*fun)());
""")

ffibuilder.compile(verbose=True)

lib.rs

extern crate nalgebra as na;

use na::DVector;

fn demo(t: f64, vec: DVector<f64>) -> DVector<f64> {
    t*vec
}

fn prop<F>(func: F) -> DVector<f64> where F:Fn(f64, DVector<f64>) -> DVector<f64>{
    // TODO: How to get the current state? In smd, it's part of the integrator
    let test = DVector::from_element(2, 2.0);
    func(2.0, test)
}

#[no_mangle]
pub extern fn prop_dyndisp(func: &Fn(f64, DVector<f64>) -> DVector<f64>) -> DVector<f64>{
    // TODO: How to get the current state? In smd, it's part of the integrator
    let test = DVector::from_element(2, 2.0);
    func(2.0, test)
}

#[no_mangle]
pub extern fn dyndisp_negate(val:bool, func: &Fn(bool) -> bool) -> bool{
    !func(val)
}

#[no_mangle]
pub extern fn dyndisp_t2(val:i32, func: &Fn() -> i32) -> i32{
    println!("t2"); // Works
    println!("t2: {}", val);  // Works with primitive
    func(); // Segfaults =(
    println!("post");
    //2*func(val)
    2
}

/*fn main() {
    println!("Hello, world!");
    println!("{}", prop(demo));
    println!("{}", prop_dyndisp(&demo));
}
*/

loader.py

from cffi import FFI

ffibuilder = FFI()

# ffibuilder.cdef('bool dyndisp_negate(bool pyval, void (*fun));')

ffibuilder.cdef("""
    extern "Python" int my_bool_func_py(bool);

    bool dyndisp_negate(bool pyval, int (*fun)(bool));
    int dyndisp_t2(int pyval, void (*fun)()); // should this be int?
""")
import _my_example

lib = ffibuilder.dlopen("../libnyxbin.so")
print(lib, dir(lib))

# should print 4
print('dyndisp_t2: {}'.format(lib.dyndisp_t2(2, _my_example.lib.my_int_func_py))) # Segfaults =(
print('dyndisp_negate: {}'.format(lib.dyndisp_negate(True, _my_example.lib.my_bool_func_py)))