Fix 'AttributeError: '_UnixSelectorEventLoop' object has no attribute… #333
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… 'call_soon' See haata#1 for a discussion. The cause of this bug is still unknown to me. But it likely has been fixed in Python 3.10. For some crazy reason, you can just keep retrying the offending call, and the attribute will magically 'reappear'.
LasseBlaauwbroek
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Oct 13, 2023
While looking at capnproto#333, I hypothesized that upgrading Cython might solve the issue. It didn't. But upgrading should still happen at some point. This is my work in progress on that. The tests pass, but there are two main things missing: Problem (1): Starting with Cython 3, you can only do `except+` or `except +reraise_kj_exception` on `extern` functions coming from C++. (This makes sense, and the way things were declared in Pycapnp wasn't too good.) As a result, I had to remove a lot of these declaration. This results in some segmentation faults, because Cython no longer detects C++ exceptions and converts them to Python exceptions in some places. To solve this, all `extern` declarations in `.pxd` files have to be examined and `except +reraise_kj_exception` clauses need to be added to anything that might throw. Previously, this was done really inconsistently. The lazy solution would be to just add the clause everywhere, but I'm not sure what the performance implications are. Problem (2): The compilation output of `python setup.py build_ext --inplace` is now full of messages like these: ``` capnp/lib/capnp.cpp: In function ‘PyObject* __pyx_f_5capnp_3lib_5capnp_18_DynamicListReader__get(__pyx_obj_5capnp_3lib_5capnp__DynamicListReader*, int64_t, int)’: capnp/lib/capnp.cpp:4871:51: warning: moving a temporary object prevents copy elision [-Wpessimizing-move] 4871 | #define __PYX_STD_MOVE_IF_SUPPORTED(x) std::move(x) | ~~~~~~~~~^~~ capnp/lib/capnp.cpp:20944:59: note: in expansion of macro ‘__PYX_STD_MOVE_IF_SUPPORTED’ 20944 | __pyx_t_2 = __pyx_f_5capnp_3lib_5capnp_to_python_reader(__PYX_STD_MOVE_IF_SUPPORTED((( ::capnp::DynamicValue::Reader)__pyx_t_7)), __pyx_t_1); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 419, __pyx_L1_error) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ capnp/lib/capnp.cpp:4871:51: note: remove ‘std::move’ call 4871 | #define __PYX_STD_MOVE_IF_SUPPORTED(x) std::move(x) | ~~~~~~~~~^~~ capnp/lib/capnp.cpp:20944:59: note: in expansion of macro ‘__PYX_STD_MOVE_IF_SUPPORTED’ 20944 | __pyx_t_2 = __pyx_f_5capnp_3lib_5capnp_to_python_reader(__PYX_STD_MOVE_IF_SUPPORTED((( ::capnp::DynamicValue::Reader)__pyx_t_7)), __pyx_t_1); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 419, __pyx_L1_error) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` There are to many `move` calls inserted. I'm not sure if this is a Cython issue, or if we are somehow annotating things wrong. Might be worth asking the Cython people. I'm not planning on working on this further in the short term. If someone wants to take over on this, feel free.
LasseBlaauwbroek
added a commit
to LasseBlaauwbroek/pycapnp
that referenced
this pull request
Oct 13, 2023
While looking at capnproto#333, I hypothesized that upgrading Cython might solve the issue. It didn't. But upgrading should still happen at some point. This is my work in progress on that. The tests pass, but there are two main things missing: Problem (1): Starting with Cython 3, you can only do `except+` or `except +reraise_kj_exception` on `extern` functions coming from C++. (This makes sense, and the way things were declared in Pycapnp wasn't too good.) As a result, I had to remove a lot of these declaration. This results in some segmentation faults, because Cython no longer detects C++ exceptions and converts them to Python exceptions in some places. To solve this, all `extern` declarations in `.pxd` files have to be examined and `except +reraise_kj_exception` clauses need to be added to anything that might throw. Previously, this was done really inconsistently. The lazy solution would be to just add the clause everywhere, but I'm not sure what the performance implications are. Problem (2): The compilation output of `python setup.py build_ext --inplace` is now full of messages like these: ``` capnp/lib/capnp.cpp: In function ‘PyObject* __pyx_f_5capnp_3lib_5capnp_18_DynamicListReader__get(__pyx_obj_5capnp_3lib_5capnp__DynamicListReader*, int64_t, int)’: capnp/lib/capnp.cpp:4871:51: warning: moving a temporary object prevents copy elision [-Wpessimizing-move] 4871 | #define __PYX_STD_MOVE_IF_SUPPORTED(x) std::move(x) | ~~~~~~~~~^~~ capnp/lib/capnp.cpp:20944:59: note: in expansion of macro ‘__PYX_STD_MOVE_IF_SUPPORTED’ 20944 | __pyx_t_2 = __pyx_f_5capnp_3lib_5capnp_to_python_reader(__PYX_STD_MOVE_IF_SUPPORTED((( ::capnp::DynamicValue::Reader)__pyx_t_7)), __pyx_t_1); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 419, __pyx_L1_error) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ capnp/lib/capnp.cpp:4871:51: note: remove ‘std::move’ call 4871 | #define __PYX_STD_MOVE_IF_SUPPORTED(x) std::move(x) | ~~~~~~~~~^~~ capnp/lib/capnp.cpp:20944:59: note: in expansion of macro ‘__PYX_STD_MOVE_IF_SUPPORTED’ 20944 | __pyx_t_2 = __pyx_f_5capnp_3lib_5capnp_to_python_reader(__PYX_STD_MOVE_IF_SUPPORTED((( ::capnp::DynamicValue::Reader)__pyx_t_7)), __pyx_t_1); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 419, __pyx_L1_error) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` There are to many `move` calls inserted. I'm not sure if this is a Cython issue, or if we are somehow annotating things wrong. Might be worth asking the Cython people. I'm not planning on working on this further in the short term. If someone wants to take over on this, feel free.
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… 'call_soon'
See haata#1 for a discussion. The cause of this bug is still unknown to me. But it likely has been fixed in Python 3.10. For some crazy reason, you can just keep retrying the offending call, and the attribute will magically 'reappear'.
I was able to reproduce this locally (in a slightly different way than in CI), and the problem goes away with this fix (no infinite loops have occurred). There are a bunch of CI tests running here: https://github.com/LasseBlaauwbroek/pycapnp/commits/fix-attribute-error-ci-test
I'd suggest waiting for them to be green to merge this.