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error_already_set::what() is now constructed lazily (pybind#1895)
* error_already_set::what() is now constructed lazily Prior to this commit throwing error_already_set was expensive due to the eager construction of the error string (which required traversing the Python stack). See pybind#1853 for more context and an alternative take on the issue. Note that error_already_set no longer inherits from std::runtime_error because the latter has no default constructor. * Do not attempt to normalize if no exception occurred This is not supported on PyPy-2.7 5.8.0. * Extract exception name via tp_name This is faster than dynamically looking up __name__ via GetAttrString. Note though that the runtime of the code throwing an error_already_set will be dominated by stack unwinding so the improvement will not be noticeable. Before: 396 ns ± 0.913 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each) After: 277 ns ± 0.549 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each) Benchmark: const std::string foo() { PyErr_SetString(PyExc_KeyError, ""); const std::string &s = py::detail::error_string(); PyErr_Clear(); return s; } PYBIND11_MODULE(foo, m) { m.def("foo", &::foo); } * Reverted error_already_set to subclass std::runtime_error * Revert "Extract exception name via tp_name" The implementation of __name__ is slightly more complex than that. It handles the module name prefix, and heap-allocated types. We could port it to pybind11 later on but for now it seems like an overkill. This reverts commit f1435c7. * Cosmit following @YannickJadoul's comments Note that detail::error_string() no longer calls PyException_SetTraceback as it is unncessary for pretty-printing the exception. * Fixed PyPy build * Moved normalization to error_already_set ctor * Fix merge bugs * Fix more merge errors * Improve formatting * Improve error message in rare case * Revert back if statements * Fix clang-tidy * Try removing mutable * Does build_mode release fix it * Set to Debug to expose segfault * Fix remove set error string * Do not run error_string() more than once * Trying setting the tracebackk to the value * guard if m_type is null * Try to debug PGI * One last try for PGI * Does reverting this fix PyPy * Reviewer suggestions * Remove unnecessary initialization * Add noexcept move and explicit fail throw * Optimize error_string creation * Fix typo * Revert noexcept * Fix merge conflict error * Abuse assignment operator * Revert operator abuse * See if we still need debug * Remove unnecessary mutable * Report "FATAL failure building pybind11::error_already_set error_string" and terminate process. * Try specifying noexcept again * Try explicit ctor * default ctor is noexcept too * Apply reviewer suggestions, simplify code, and make helper method private * Remove unnecessary include * Clang-Tidy fix * detail::obj_class_name(), fprintf with [STDERR], [STDOUT] tags, polish comments * consistently check m_lazy_what.empty() also in production builds * Make a comment slightly less ambiguous. * Bug fix: Remove `what();` from `restore()`. It sure would need to be guarded by `if (m_type)`, otherwise `what()` fails and masks that no error was set (see update unit test). But since `error_already_set` is copyable, there is no point in releasing m_type, m_value, m_trace, therefore we can just as well avoid the runtime overhead of force-building `m_lazy_what`, it may never be used. * Replace extremely opaque (unhelpful) error message with a truthful reflection of what we know. * Fix clang-tidy error [performance-move-constructor-init]. * Make expected error message less specific. * Various changes. * bug fix: error_string(PyObject **, ...) * Putting back the two eager PyErr_NormalizeException() calls. * Change error_already_set() to call pybind11_fail() if the Python error indicator not set. The net result is that a std::runtime_error is thrown instead of error_already_set, but all tests pass as is. * Remove mutable (fixes oversight in the previous commit). * Normalize the exception only locally in error_string(). Python 3.6 & 3.7 test failures expected. This is meant for benchmarking, to determine if it is worth the trouble looking into the failures. * clang-tidy: use auto * Use `gil_scoped_acquire_local` in `error_already_set` destructor. See long comment. * For Python < 3.8: `PyErr_NormalizeException` before `PyErr_WriteUnraisable` * Go back to replacing the held Python exception with then normalized exception, if & when needed. Consistently document the side-effect. * Slightly rewording comment. (There were also other failures.) * Add 1-line comment for obj_class_name() * Benchmark code, with results in this commit message. function #calls test time [s] μs / call master pure_unwind 729540 1.061 14.539876 err_set_unwind_err_clear 681476 1.040 15.260282 err_set_error_already_set 508038 1.049 20.640525 error_already_set_restore 555578 1.052 18.933288 pr1895_original_foo 244113 1.050 43.018168 PR / master PR pybind#1895 pure_unwind 736981 1.054 14.295685 98.32% err_set_unwind_err_clear 685820 1.045 15.237399 99.85% err_set_error_already_set 661374 1.046 15.811879 76.61% error_already_set_restore 669881 1.048 15.645176 82.63% pr1895_original_foo 318243 1.059 33.290806 77.39% master @ commit ad146b2 Running tests in directory "/usr/local/google/home/rwgk/forked/pybind11/tests": ============================= test session starts ============================== platform linux -- Python 3.9.10, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- /usr/bin/python3 cachedir: .pytest_cache rootdir: /usr/local/google/home/rwgk/forked/pybind11/tests, configfile: pytest.ini collecting ... collected 5 items test_perf_error_already_set.py::test_perf[pure_unwind] PERF pure_unwind,729540,1.061,14.539876 PASSED test_perf_error_already_set.py::test_perf[err_set_unwind_err_clear] PERF err_set_unwind_err_clear,681476,1.040,15.260282 PASSED test_perf_error_already_set.py::test_perf[err_set_error_already_set] PERF err_set_error_already_set,508038,1.049,20.640525 PASSED test_perf_error_already_set.py::test_perf[error_already_set_restore] PERF error_already_set_restore,555578,1.052,18.933288 PASSED test_perf_error_already_set.py::test_perf[pr1895_original_foo] PERF pr1895_original_foo,244113,1.050,43.018168 PASSED ============================== 5 passed in 12.38s ============================== pr1895 @ commit 8dff51d Running tests in directory "/usr/local/google/home/rwgk/forked/pybind11/tests": ============================= test session starts ============================== platform linux -- Python 3.9.10, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- /usr/bin/python3 cachedir: .pytest_cache rootdir: /usr/local/google/home/rwgk/forked/pybind11/tests, configfile: pytest.ini collecting ... collected 5 items test_perf_error_already_set.py::test_perf[pure_unwind] PERF pure_unwind,736981,1.054,14.295685 PASSED test_perf_error_already_set.py::test_perf[err_set_unwind_err_clear] PERF err_set_unwind_err_clear,685820,1.045,15.237399 PASSED test_perf_error_already_set.py::test_perf[err_set_error_already_set] PERF err_set_error_already_set,661374,1.046,15.811879 PASSED test_perf_error_already_set.py::test_perf[error_already_set_restore] PERF error_already_set_restore,669881,1.048,15.645176 PASSED test_perf_error_already_set.py::test_perf[pr1895_original_foo] PERF pr1895_original_foo,318243,1.059,33.290806 PASSED ============================== 5 passed in 12.40s ============================== clang++ -o pybind11/tests/test_perf_error_already_set.os -c -std=c++17 -fPIC -fvisibility=hidden -Os -flto -Wall -Wextra -Wconversion -Wcast-qual -Wdeprecated -Wnon-virtual-dtor -Wunused-result -isystem /usr/include/python3.9 -isystem /usr/include/eigen3 -DPYBIND11_STRICT_ASSERTS_CLASS_HOLDER_VS_TYPE_CASTER_MIX -DPYBIND11_TEST_BOOST -Ipybind11/include -I/usr/local/google/home/rwgk/forked/pybind11/include -I/usr/local/google/home/rwgk/clone/pybind11/include /usr/local/google/home/rwgk/forked/pybind11/tests/test_perf_error_already_set.cpp clang++ -o lib/pybind11_tests.so -shared -fPIC -Os -flto -shared ... Debian clang version 13.0.1-3+build2 Target: x86_64-pc-linux-gnu Thread model: posix * Changing call_repetitions_target_elapsed_secs to 0.1 for regular unit testing. * Adding in `recursion_depth` * Optimized ctor * Fix silly bug in recurse_first_then_call() * Add tests that have equivalent PyErr_Fetch(), PyErr_Restore() but no try-catch. * Add call_error_string to tests. Sample only recursion_depth 0, 100. * Show lazy-what speed-up in percent. * Include real_work in benchmarks. * Replace all PyErr_SetString() with generate_python_exception_with_traceback() * Better organization of test loops. * Add test_error_already_set_copy_move * Fix bug in newly added test (discovered by clang-tidy): actually use move ctor * MSVC detects the unreachable return * change test_perf_error_already_set.py back to quick mode * Inherit from std::exception (instead of std::runtime_error, which does not make sense anymore with the lazy what) * Special handling under Windows. * print with leading newline * Removing test_perf_error_already_set (copies are under rwgk/rwgk_tbx@7765113). * Avoid gil and scope overhead if there is nothing to release. * Restore default move ctor. "member function" instead of "function" (note that "method" is Python terminology). * Delete error_already_set copy ctor. * Make restore() non-const again to resolve clang-tidy failure (still experimenting). * Bring back error_already_set copy ctor, to see if that resolves the 4 MSVC test failures. * Add noexcept to error_already_set copy & move ctors (as suggested by @Skylion007 IIUC). * Trying one-by-one noexcept copy ctor for old compilers. * Add back test covering copy ctor. Add another simple test that exercises the copy ctor. * Exclude more older compilers from using the noexcept = default ctors. (The tests in the previous commit exposed that those are broken.) * Factor out & reuse gil_scoped_acquire_local as gil_scoped_acquire_simple * Guard gil_scoped_acquire_simple by _Py_IsFinalizing() check. * what() GIL safety * clang-tidy & Python 3.6 fixes * Use `gil_scoped_acquire` in dtor, copy ctor, `what()`. Remove `_Py_IsFinalizing()` checks (they are racy: python/cpython#28525). * Remove error_scope from copy ctor. * Add `error_scope` to `get_internals()`, to cover the situation that `get_internals()` is called from the `error_already_set` dtor while a new Python error is in flight already. Also backing out `gil_scoped_acquire_simple` change. * Add `FlakyException` tests with failure triggers in `__init__` and `__str__` THIS IS STILL A WORK IN PROGRESS. This commit is only an important resting point. This commit is a first attempt at addressing the observation that `PyErr_NormalizeException()` completely replaces the original exception if `__init__` fails. This can be very confusing even in small applications, and extremely confusing in large ones. * Tweaks to resolve Py 3.6 and PyPy CI failures. * Normalize Python exception immediately in error_already_set ctor. For background see: pybind#1895 (comment) * Fix oversights based on CI failures (copy & move ctor initialization). * Move @pytest.mark.xfail("env.PYPY") after @pytest.mark.parametrize(...) * Use @pytest.mark.skipif (xfail does not work for segfaults, of course). * Remove unused obj_class_name_or() function (it was added only under this PR). * Remove already obsolete C++ comments and code that were added only under this PR. * Slightly better (newly added) comments. * Factor out detail::error_fetch_and_normalize. Preparation for producing identical results from error_already_set::what() and detail::error_string(). Note that this is a very conservative refactoring. It would be much better to first move detail::error_string into detail/error_string.h * Copy most of error_string() code to new error_fetch_and_normalize::complete_lazy_error_string() * Remove all error_string() code from detail/type_caster_base.h. Note that this commit includes a subtle bug fix: previously error_string() restored the Python error, which will upset pybind11_fail(). This never was a problem in practice because the two PyType_Ready() calls in detail/class.h do not usually fail. * Return const std::string& instead of const char * and move error_string() to pytypes.h * Remove gil_scope_acquire from error_fetch_and_normalize, add back to error_already_set * Better handling of FlakyException __str__ failure. * Move error_fetch_and_normalize::complete_lazy_error_string() implementation from pybind11.h to pytypes.h * Add error_fetch_and_normalize::release_py_object_references() and use from error_already_set dtor. * Use shared_ptr for m_fetched_error => 1. non-racy, copy ctor that does not need the GIL; 2. enables guard against duplicate restore() calls. * Add comments. * Trivial renaming of a newly introduced member function. * Workaround for PyPy * Bug fix (oversight). Only valgrind got this one. * Use shared_ptr custom deleter for m_fetched_error in error_already_set. This enables removing the dtor, copy ctor, move ctor completely. * Further small simplification. With the GIL held, simply deleting the raw_ptr takes care of everything. * IWYU cleanup ``` iwyu version: include-what-you-use 0.17 based on Debian clang version 13.0.1-3+build2 ``` Command used: ``` iwyu -c -std=c++17 -DPYBIND11_TEST_BOOST -Iinclude/pybind11 -I/usr/include/python3.9 -I/usr/include/eigen3 include/pybind11/pytypes.cpp ``` pytypes.cpp is a temporary file: `#include "pytypes.h"` The raw output is very long and noisy. I decided to use `#include <cstddef>` instead of `#include <cstdio>` for `std::size_t` (iwyu sticks to the manual choice). I ignored all iwyu suggestions that are indirectly covered by `#include <Python.h>`. I manually verified that all added includes are actually needed. Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com> Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>
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