8000 bpo-42296: On Windows, fix CTRL+C regression (GH-23257) · python/cpython@d96a7a8 · GitHub
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bpo-42296: On Windows, fix CTRL+C regression (GH-23257)
On Windows, fix a regression in signal handling which prevented to interrupt a program using CTRL+C. The signal handler can be run in a thread different than the Python thread, in which case the test deciding if the thread can handle signals is wrong. On Windows, _PyEval_SignalReceived() now always sets eval_breaker to 1 since it cannot test _Py_ThreadCanHandleSignals(), and eval_frame_handle_pending() always calls _Py_ThreadCanHandleSignals() to recompute eval_breaker.
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‎Misc/NEWS.d/next/Core and Builtins/2020-11-13-13-53-11.bpo-42296.DuGrLJ.rst

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On Windows, fix a regression in signal handling which prevented to interrupt
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a program using CTRL+C. The signal handler can be run in a thread different
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than the Python thread, in which case the test deciding if the thread can
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handle signals is wrong.

‎Python/ceval.c

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@@ -203,13 +203,18 @@ UNSIGNAL_PENDING_CALLS(PyInterpreterState *interp)
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static inline void
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SIGNAL_PENDING_SIGNALS(PyInterpreterState *interp)
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SIGNAL_PENDING_SIGNALS(PyInterpreterState *interp, int force)
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{
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struct _ceval_runtime_state *ceval = &interp->runtime->ceval;
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struct _ceval_state *ceval2 = &interp->ceval;
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_Py_atomic_store_relaxed(&ceval->signals_pending, 1);
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/* eval_breaker is not set to 1 if thread_can_handle_signals() is false */
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COMPUTE_EVAL_BREAKER(interp, ceval, ceval2);
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if (force) {
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_Py_atomic_store_relaxed(&ceval2->eval_breaker, 1);
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}
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else {
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/* eval_breaker is not set to 1 if thread_can_handle_signals() is false */
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COMPUTE_EVAL_BREAKER(interp, ceval, ceval2);
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}
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}
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@@ -559,10 +564,22 @@ PyEval_RestoreThread(PyThreadState *tstate)
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void
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_PyEval_SignalReceived(PyInterpreterState *interp)
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{
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#ifdef MS_WINDOWS
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// bpo-42296: On Windows, _PyEval_SignalReceived() is called from a signal
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// handler which can run in a thread different than the Python thread, in
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// which case _Py_ThreadCanHandleSignals() is wrong. Ignore
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// _Py_ThreadCanHandleSignals() and always set eval_breaker to 1.
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//
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// The next eval_frame_handle_pending() call will call
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// _Py_ThreadCanHandleSignals() to recompute eval_breaker.
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int force = 1;
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#else
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int force = 0;
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#endif
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/* bpo-30703: Function called when the C signal handler of Python gets a
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signal. We cannot queue a callback using _PyEval_AddPendingCall() since
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that function is not async-signal-safe. */
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SIGNAL_PENDING_SIGNALS(interp);
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SIGNAL_PENDING_SIGNALS(interp, force);
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}
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/* Push one item onto the queue while holding the lock. */
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UNSIGNAL_PENDING_SIGNALS(tstate->interp);
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if (_PyErr_CheckSignalsTstate(tstate) < 0) {
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/* On failure, re-schedule a call to handle_signals(). */
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SIGNAL_PENDING_SIGNALS(tstate->interp);
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SIGNAL_PENDING_SIGNALS(tstate->interp, 0);
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return -1;
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}
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return 0;
@@ -948,6 +965,17 @@ eval_frame_handle_pending(PyThreadState *tstate)
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return -1;
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}
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#ifdef MS_WINDOWS
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// bpo-42296: On Windows, _PyEval_SignalReceived() can be called in a
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// different thread than the Python thread, in which case
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// _Py_ThreadCanHandleSignals() is wrong. Recompute eval_breaker in the
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// current Python thread with the correct _Py_ThreadCanHandleSignals()
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// value. It prevents to interrupt the eval loop at every instruction if
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// the current Python thread cannot handle signals (if
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// _Py_ThreadCanHandleSignals() is false).
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COMPUTE_EVAL_BREAKER(tstate->interp, ceval, ceval2);
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#endif
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return 0;
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}
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