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compute error formatting state when python is initialized - #1936
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The hint is computed by R code, which can process events and re-enter conditionMessage_from_py_exception(); a re-entrant call deadlocked (libstdc++) or aborted (libc++) on the static's init guard. Fixes #1935.
Compute the error hint in R and look up traceback.format_exception_only() during initialization, instead of in function-local static initializers on the first error. Both initializers could run R code (the hint function, or the import hook's callback for 'traceback'), and a Python error formatted from there re-entered the static's init guard.
kevinushey
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Cache the error hint when the namespace loads and read it from C++ during initialization. Keep the existing eight-argument R and native interfaces so callers that initialize Python directly continue to work.
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conditionMessage_from_py_exception()set up two function-local statics on the first Python error of a session, and both of their initializers could run R code:.py_last_error_hint();traceback.format_exception_only, whose first import oftracebackruns reticulate's import hook, which callspy_module_onload()in R.R code can process events. If an event handler formats another Python error in that window, the nested call waits on the static's own init guard: libstdc++ deadlocks and libc++ aborts. RStudio Server hit the deadlock while answering an Environment pane request as the Python REPL started; see #1935 for the backtrace.
Both are now set when Python is initialized. R computes the hint before Python starts and passes it to
py_initialize().py_initialize()looks uptraceback.format_exception_onlybefore anything that can raise a Python error, and before reticulate's import hook is installed. Formatting an error no longer computes either one.Testing
Two new tests in
test-python-exceptions.R, each run in a freshcallrsession:.py_last_error_hint()with a function that errors, after Python has started, then formats a Python error. On reticulate 1.47.0 the message is the replacement's error; with this branch it's the Python error plus the hint.py_register_load_hook("traceback", ...)hook that formats another Python error, then raises a first error. On macOS with 1.47.0 the child aborts with__cxa_guard_acquire detected recursive initialization; with this branch it passes.The rest of
test-python-exceptions.Rpasses. In the full suite the only failures were snapshot tests intest-py_require.R, which fail locally because of my uv version and default Python (3.13 vs 3.12).Fixes #1935.