How to interrupt python interpreter embedded in C++ application

Question

We have a C++ QT application, we embedded python in it. We provided two interfaces to the user 1. Execute file 2. Stop execution. We execute a python file in a non GUI thread, using PyRun_FileExFlags. We would like to interrupt python file execution (assume python file has an infinite loop, it never completes execution). How to interrupt?

We tried following 1. In main thread set trace using PyEval_SetTrace 2. (if user click on Stop execution) In the trace call back function we set error "PyErr_SetString"

1:setting trace function

PyGILState_STATE state;
state = PyGILState_Ensure();                
PyEval_SetTrace(TraceHook, NULL);
PyGILState_Release(state);

2:trace function

int TraceHook(PyObject *obj, PyFrameObject *frame, int what, PyObject *arg)
{
if (b_isInterrupted)
{
PyGILState_STATE state;
state = PyGILState_Ensure();
PyErr_SetString(PyExc_KeyboardInterrupt, "Python Interrupted.");
PyGILState_Release(state);
}
return 0;
}

Python execution is not interrupted. I expect python execution to interrupt.

Davis Herring · Accepted Answer · 2019-01-31 02:00:21Z

3

PyEval_SetTrace affects the current thread only.

You want PyErr_SetInterrupt. It interrupts (what Python considers to be) the main thread, regardless of the calling thread (which need not bother with the GIL).

answered Jan 31, 2019 at 2:00

Davis Herring

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4 Comments

srinivas M Over a year ago

Thanks Davis, how to interrupt the thread (which is not main thread) which is executing PyRun_FileExFlags

Davis Herring Over a year ago

@srinivasM: I don’t think Python knows more than what thread called Py_Initialize—can you arrange for it to be the same one?

srinivas M Over a year ago

Thanks @Davis: it worked for main thread. Can you suggest if there is a way to stop other threads?

Davis Herring Over a year ago

@srinivasM: There is PyThreadState_SetAsyncExc, but I don’t know how to get its id argument.

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