New submission from Marc Horowitz <mhorow...@gmail.com>:
I discovered this bug working with panda3d. I've attached a short
python script which demonstrates the problem. After installing
panda3d, run the script, and then hit q in the window which appears.
You'll see that none of the cleanup code after the 'run()' main loop
runs.
The underlying cause is in how panda3d uses the C API. It's got code
like this (in src/pipeline/thread.cxx):
// Call the user's function.
result = PyObject_Call(function, args, NULL);
if (result == (PyObject *)NULL && PyErr_Occurred()) {
// We got an exception. Move the exception from the current
// thread into the main thread, so it can be handled there.
PyObject *exc, *val, *tb;
PyErr_Fetch(&exc, &val, &tb);
thread_cat.error()
<< "Exception occurred within " << *this << "\n";
// Temporarily restore the exception state so we can print a
// callback on-the-spot.
Py_XINCREF(exc);
Py_XINCREF(val);
Py_XINCREF(tb);
PyErr_Restore(exc, val, tb);
PyErr_Print();
...
If the code being called (generally a panda3d task function or event
handler) calls sys.exit, the PyErr_Print() never returns. This is
surprising, as the the documentation never mentions that a function
with an innocuous name like "Print" might never return.
However, I don't think this is a panda3d bug; I think that the
function as documented is the way it should behave. Otherwise, the
vast majority of calls to this method will need to look like
if (!PyErr_ExceptionMatches(PyExc_SystemExit)) {
PyErr_PrintEx(1);
}
which seems like a poor abstraction.
Another unexpected side effect is when python is used with the -i
flag. Because of the way this alters the normal exit behavior, the
code runs the way I'd expect, and the cleanup code in the test
application *does* run. It seems rather strange to me that cleanup
code should run or not run based on the -i flag.
I believe the fix for all this is that PyErr_PrintEx be changed to
behave as documented, *not* call handle_system_exit() when passed
SystemExit, and instead in the places where the interpreter main loop
is run, followed by PyErr_PrintEx(), that SystemExit is special cased
in those specific locations as needed.
----------
components: Interpreter Core
files: exit_test.py
messages: 122846
nosy: Marc.Horowitz
priority: normal
severity: normal
status: open
title: PyErr_PrintEx exits silently when passed SystemExit exception
type: behavior
versions: Python 2.6
Added file: http://bugs.python.org/file19875/exit_test.py
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue10582>
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