Running opencv-python script in sub-interpreter causes a hang

[Ashwin Prasad]

Hi,

We are hosting the python interpreter(version 2.7.13) in a C application
and calling a python function that has some calls to opencv-python
functions (Representative code fragments are below). When the python
function is called in the main interpreter, it works fine. However, when
the it is called in a sub-interpreter, it hangs!

The C code is as follows:

Py_Initialize();
PyEval_InitThreads();

#If RUN_IN_SUBINTERPRETER
PyThreadState* threadState = Py_NewInterpreter();
PyThreadState *mainState = PyThreadState_Swap(threadState);
#endif

pName = PyString_FromString("abc_module");
pModule = PyImport_Import(pName);
pDict = PyModule_GetDict(pModule);
pFunc = PyDict_GetItemString(pDict, "abc_function");
pyList = GenerateArgList();
PyObject* pArgs = PyTuple_New(1);
PyTuple_SetItem(pArgs, 0, pyList);

pValue = PyObject_CallObject(pFunc, pArgs);


The Python code is as follows:
import sys
import cv2
import numpy as np

def abc_function(list):
array = np.asarray(list)
array = np.reshape(array, (100, 200, 4)).astype(np.uint8)
array = abc_function_core(array)
return array

def abc_function_core(array):
# array is passed to the below functions
cv2.resize(....)
cv2.cvtColor(...)
cv2.equalizeHist(...)
cv2.CascadeClassifier.detectMultiScale(...)
cv2.rectangle(...)
return array
Is there any known incompatibility between the opencv-python package and
sub-interpreters? We did find that there are some packages that are
incompatible with sub-interpreters but we couldn't find any such
information about opencv-python.

My sincere apologies if this is not the appropriate group to be posting
this question to. If that is the case, please let me know which group I
should ask this question on.

Thanks in advance for the help!
Ashwin