Py_AddPendingCall Inserted Function Never Called in 3.8, works in 3.6

[ChrisMorton]

BPO	43482
Nosy	@chris Morton

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-03-12.22:11:40.187>
labels = ['expert-C-API', 'type-bug', '3.8']
title = 'Py_AddPendingCall Inserted Function Never Called in 3.8, works in 3.6'
updated_at = <Date 2021-03-15.03:29:17.721>
user = 'https://github.com/ChrisMorton'

bugs.python.org fields:

activity = <Date 2021-03-15.03:29:17.721>
actor = 'chrisgmorton'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2021-03-12.22:11:40.187>
creator = 'chrisgmorton'
dependencies = []
files = []
hgrepos = []
issue_num = 43482
keywords = []
message_count = 2.0
messages = ['388559', '388704']
nosy_count = 1.0
nosy_names = ['chrisgmorton']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43482'
versions = ['Python 3.8']

[ChrisMorton]

Building code on Mac OSX or Linux Ubuntu 16.04

#include <Python.h>
#include <thread>
#include <chrono>
#include <iostream>

// MacOSX build:
// g++ stop.cpp -I <prod root dir>/include/pythonX.X -L <prod root dir>/lib -lpythonX.X -o stop
// Linuxe requires addtional linkage:
// -lpthread

void RunPythonScript()
{
    PyRun_SimpleString("# import sys \n"
                       "import time \n"
                       "# sys.setcheckinterval(-1) \n"
                       "while True: \n"
                       "    print('Running!') \n"
                       "    time.sleep(1) \n"
                       );

std::cout \<\< "Terminating Python Interpreter." \<\< std::endl;

}

int Stop(void *)
{
    std::cout << "We threw an exception." <<std::endl;    
    PyErr_SetInterrupt();
    PyErr_SetString(PyExc_RuntimeError, "Stop Python Execution.");
    return -1;

}

int main (int argc, char *argv[])
{

Py_Initialize(); // The Python Interpreter must be created in the main thread.

std::thread th(&RunPythonScript);    // Now execute our python scipt in a thread.

std::cout << "Python has started!" << std::endl;    
std::this_thread::sleep_for(std::chrono::seconds(5));

std::cout << "Asking Python to exit." << std::endl;

    PyGILState_STATE state = PyGILState_Ensure();    
    int r = Py_AddPendingCall(&Stop, NULL); // inject our Stop routine
    std::cout << r <<std::endl;
    PyGILState_Release(state);
    
    th.join(); // Wait for the thread to catch up. 

    Py_Finalize();

    std::cout << "Exiting Main Function." << std::endl;
    
    std::this_thread::sleep_for(std::chrono::seconds(2));
    
return 0;
}

Linking against 3.6 and executing leads to the successful interruption of Python code execution:

Python has started!
Running!
Running!
Running!
Running!
Running!
Asking Python to exit.
0
We threw an exception.
Traceback (most recent call last):
  File "<string>", line 6, in <module>
RuntimeError: Stop Python Execution.
Terminating Python Interpreter.
Exiting Main Function.

The Stop function is never called with the same code linked against Python 3.8.

[ChrisMorton]

I should add that Py_AddPendingCall returns 0 in both cases.

[kumaraditya303]

Duplicate of #95820