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Don't abort on FT2Font weakref. - #9074
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A minor comment, but this works for me.
| */ | ||
| static NPY_INLINE int mpl_PyFile_DupClose(PyObject *file, FILE *handle, mpl_off_t orig_pos) | ||
| { | ||
| PyObject *type = NULL, *value = NULL, *tb = NULL; |
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These should probably get some differentiating name, like an orig_ prefix or something.
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grepping through https://github.com/python/cpython/blob/f320be77ffb73e3b9e7fc98c37b8df3975d84b40/Modules/_io/fileio.c shows that cpython tends to stash the current exception (if any) in *exc, *val, *tb (but not without a prefix). We're not shadowing anything anyways...
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Sure, but those are generally around one other call, whereas this one is around almost an entire function body.
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| static NPY_INLINE int mpl_PyFile_CloseFile(PyObject *file) | ||
| { | ||
| PyObject *type, *value, *tb; |
Currently,
import weakref, matplotlib.ft2font
weakref.ref(matplotlib.ft2font.FT2Font("/usr/share/fonts/TTF/DejaVuSans.ttf"))
aborts Py3 with
terminate called after throwing an instance of 'char const*'
Fatal Python error: Aborted
whereas on Py2 a normal `TypeError: cannot create weak reference to
'matplotlib.ft2font.FT2Font' object` is raised.
This is because the following happens:
- Py3 sets the TypeError for failure to create a weakref.
- The FT2Font object gets GC'd as nothing is referring to it (yes,
creating a weakref to a temporary is a bit silly).
- The FT2Font destructor calls close_file_callback, which calls
mpl_PyFile_DupClose, which calls PyObject_AsFileDescriptor... which,
on Py3, calls the fileno() method on the file object.
- PyObject_AsFileDescriptor fails because the originally set TypeError
has not been cleared, so mpl_PyFile_DupClose likewise fails, causing
close_file_callback to throw a C++ exception.
Instead, carefully stash and restore the current exception state, both
in mpl_PyFile_DupClose, and likewise below, in mpl_PyFile_CloseFile (the
latter is needed because otherwise PyObject_CallMethod will clear the
exception, cf comment in CPython's Objects/abstract.c:
/* PyObject_Call() must not be called with an exception set,
because it may clear it (directly or indirectly) and so the
caller loses its exception */
Note that if an exception *actually* gets raised by mpl_PyFile_DupClose
or mpl_PyFile_CloseFile, it will overwrite the TypeError. Strictly
speaking, on Py3, it may be preferrable to chain the exceptions, but
this seems a bit overkill (mostly, I just want to avoid aborting the
whole Python process).
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Currently,
aborts Py3 with
whereas on Py2 a normal
TypeError: cannot create weak reference to 'matplotlib.ft2font.FT2Font' objectis raised.This is because the following happens:
creating a weakref to a temporary is a bit silly).
mpl_PyFile_DupClose, which calls PyObject_AsFileDescriptor... which,
on Py3, calls the fileno() method on the file object.
has not been cleared, so mpl_PyFile_DupClose likewise fails, causing
close_file_callback to throw a C++ exception.
Instead, carefully stash and restore the current exception state, both
in mpl_PyFile_DupClose, and likewise below, in mpl_PyFile_CloseFile (the
latter is needed because otherwise PyObject_CallMethod will clear the
exception, cf comment in CPython's Objects/abstract.c:
Note that if an exception actually gets raised by mpl_PyFile_DupClose
or mpl_PyFile_CloseFile, it will overwrite the TypeError. Strictly
speaking, on Py3, it may be preferrable to chain the exceptions, but
this seems a bit overkill (mostly, I just want to avoid aborting the
whole Python process).
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