c_side.cpp

void mxnet_detect(const cv::Mat& mat) {
    PyObject *pRunnerModule, *pRunnerFunc, *pRunnerResult;

    Py_SetProgramName("mtcnn-bridge");
    Py_Initialize();
    PyEval_InitThreads();
    import_array();

    Py_BEGIN_ALLOW_THREADS
    
    PyObject* moduleName = PyString_FromString((char*)"mtcnn_runner");
    pRunnerModule = PyImport_Import(moduleName);
    pRunnerFunc = PyObject_GetAttrString(pRunnerModule,(char*)"detect");
    npyIntp dims[] = {1080,1920,3};
    PyObject *pArray = PyArraySimpleNewFromData(3, dims, NPYUINT8, mat.data);

    PyObject *arglist = Py_BuildValue("(O)", pArray);
    pRunnerResult = PyObject_CallObject(pRunnerFunc, arglist);
    
    Py_END_ALLOW_THREADS
    
    Py_Finalize();
}

mtcnn_runner.py

import cv2
from pprint import pprint as pp
import mxnet as mx
from mtcnn_detector import MtcnnDetector

detector = MtcnnDetector(model_folder='model', ctx=mx.cpu(0), num_worker = 1 , accurate_landmark = False)

def detect(img):
    # somehere inside detect_face, a threadpool is used
    # specifically, the built-in multi-threading library and the Pool.map function
    results = detector.detect_face(img)