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List:       python-bugs-list
Subject:    [issue7173] Cython compiler run crashes CPython 3.1.1 and 3.2
From:       Stefan Behnel <report () bugs ! python ! org>
Date:       2010-01-31 12:39:05
Message-ID: 1264941545.53.0.244287005925.issue7173 () psf ! upfronthosting ! co ! za
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Stefan Behnel <scoder@users.sourceforge.net> added the comment:

I'll add a couple of comments about the relevant parts of the code that appears to \
trigger the crash.

The code runs through the parse tree and applies transformations to it.

1) For node matching, we use a dispatcher (in Visitor.py) that looks up methods for \
node class names (or the nearest matching class in its MRO hierarchy), e.g. a plain \
"Node" type would be handled by a "visit_Node" method, whereas an ExprNode(Node) type \
would match "visit_ExprNode" if it exists and "visit_Node" otherwise. The handler \
then recursively calls back into the dispatch code to visit its children.

For performance reasons, we sometimes reuse existing methods for this through \
assignment, e.g. instead of reimplementing the default fallback "visit_Node" all over \
the place, we assign an existing superclass method to it as in "visit_Node = \
VisitorTransform.recurse_to_children". This may or may not have an impact on this \
problem (it shouldn't - normally).

So far, all of this appears to work perfectly fine also in Py3. It's the next step \
that seems to be required to trigger the crash.

2) To specify assertions in our test suite, we use an XPath-like language for node \
tests (poor man's Schematron, sort-of). The implementation in TreePath.py (based on \
"ElementPath" in ElementTree 1.3) makes heavy use of generators to traverse the tree. \
It is used by the TreeAssertVisitor in TestUtils.py, which is itself a recursive tree \
visitor (as described above).

So the situation is as follows. Cython traverses the parse tree recursively, several \
times in a pipeline, dispatching to methods that further recurse into the tree. One \
of the pipeline steps is the tree assertion visitor, which, on matching functions, \
applies the generator-based path language to the tree, that tries to find nodes by \
iterating over a chain of generators.

At some point in this process, somehow, sys.exc_info gets corrupted, and the \
doctest/unittest framework crashes the runtime with a segfault when trying to print \
an exception (raised unexpectedly by the "pure" test).

I hope this makes it clearer a) what happens and b) why it's not easy to cut this \
down into a simple test case. As the previous comments show, it's already hard enough \
to reproduce it reliably with a reduced test setup.

Please do not hesitate to contact me if you need any further information.

----------

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